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1
Bell, Andrew Forbes. "Patterns of volcano-tectonic seismicity at basaltic volcanoes". Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1444163/.
Testo completoAbstract (sommario):
Accelerating rates of volcano-tectonic (VT) earthquakes are a common precursor to volcanic eruptions and reflect fracture growth within the edifice. Theoretical models interpret the patterns in terms of failure of the volcanic edifice under the magmatic load and promise improved eruption forecasting. However, many eruptions at frequently active basaltic volcanoes are reported to begin with little change in the rate of VT earthquakes, apparently in conflict with edifice failure models. This thesis investigates the spatial and temporal patterns of VT earthquakes associated with eruptive and intrusive dyke injection at three of the best studied basaltic volcanoes, Kilauea and Mauna Loa (Hawaii) and Mt Etna (Sicily), in order to constrain the processes controlling the approach to eruption and test the applicability of edifice failure models. Approximately one third of dyke injection events are preceded by more than 4 weeks of exponentially accelerating rates of earthquakes. The trends are consistent with a model where deformation is controlled by the growth of independent fractures driven by increased magma pressure. Relations between acceleration parameters, such as the total number of earthquakes and characteristic timescale, provide information as to the likely timing of dyke injection. No evidence is found for short-term power-law accelerations in the rates of earthquakes thought to correspond to the linkage of fractures and observed at subduction zone volcanoes. The seismicity associated with the remaining events has characteristics indicating that flank instability is involved in triggering injection, either through the progressive reduction in the horizontal compressive stress by flank slip or through an episode of accelerated flank slip (a so-called slow earthquake). These observations suggest that: 1) an edifice failure model provides a good basis for understanding the approach to basaltic eruptions, but 2) at unstable volcanoes, modifications of the model are required to account for the influence of flank slip.
2
Gulmammadov, Rashad. "Seismic geomechanics of mud volcanoes". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/seismic-geomechanics-of-mud-volcanoes(e579a3af-0881-4f52-b14a-dd360304f337).html.
Testo completoAbstract (sommario):
Mud volcanoes constitute an important component of petroliferous basins and their understanding is essential for successful exploration and development of hydrocarbon fields. They occur in both extensional and compressive tectonic settings, along with passive and active continental margins. Although extensive research exists on the geochemistry, geomorphology and stratigraphic evolution of these localized fluid flow structures, little is known about their geomechanical characteristics. This research investigates the geomechanics of mud volcanoes from the South Caspian Basin and West Nile Delta. This is achieved by establishing a workflow for geomechanical assessment of mud volcanoes using a P-wave velocity dataset from across the mud volcano within the offshore South Caspian Basin. This objective is developed further with the availability of seismic and wellbore data from around the Giza mud volcano, offshore West Nile Delta. Preliminary results of this study from the South Caspian Basin enable confidence in estimating the realistic magnitudes of elastic rock properties, stresses and fluid pressures from empirical and analytical correlations. Moreover, analysis of the variations in fluid pressures allow the fluid flow models around the mud volcano to be constrained and their gradients provide preliminary estimates of the drilling window. Structural and stratigraphic analysis around the Giza mud volcano offers insight into the formation of the mud volcano during the Quaternary and how the fault networks on the hanging wall of the arcuate tectonic fault have acted as conduits for primarily the pre-Pliocene fluids exploiting the areas of weakness along the hanging wall of the fault by entraining the Pliocene sediments. Fluid pressure evaluation reveals small overpressures caused by disequilibrium compaction. Further analysis offers insight into the critical fluid pressures that control fault movement, the stresses responsible for rock deformation around the wellbore and the width of the drilling window constrained by the fracturing of the strata. Analysis presented here provides details on the geomechanical significance of mud volcano environments, with implications for engineering practices. Overall, findings contribute to a systematic understanding of mud volcano settings not only from a field exploration and development point of view, but also at a wider scale for basin analysis and relatively small scale for play analysis.
3
Auer, Sara Lynn. "Diverse oxygen isotope values and high magmatic water contents within the volcanic record of Klyuschevskoy Volcano, Kamchatka, Russia /". Connect to title online (Scholars' Bank), 2007. http://handle.net/1794/6054.
Testo completo
4
Burrell, Rhian. "Volcanic instability and associated uncertainties at Soufrière Hills Volcano, Montserrat and other volcanoes". Thesis, Lancaster University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435873.
Testo completo
5
Lane, Lucille Richards. "Hazard Vulnerability in Socio-Economic Context: An Example from Ecuador". [Tampa, Fla. : s.n.], 2003. http://purl.fcla.edu/fcla/etd/SFE0000076.
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6
Beachly, Matthew William 1986. "The Upper Crustal P-wave Velocity Structure of Newberry Volcano, Central Oregon". Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11475.
Testo completoAbstract (sommario):
xii, 98 p. : ill. (some col.)The upper-crustal seismic-velocity structure of Newberry volcano, central Oregon, is imaged using P-wave travel time tomography. The inversion combines a densely-spaced seismic line collected in 2008 with two USGS seismic experiments from the 1980s. A high-velocity ring (7 km EW by 5 km NS) beneath the inner caldera faults suggests an intrusive ring complex 200 to 500 m thick. Within this ring shallow low velocities (<2 km depth) are interpreted as caldera fill and a subsided block. High velocities below 2 km depth could be intrusive complexes. There appears to be a low-velocity body at 3-6 km depth beneath the center of the volcano. This region is poorly resolved in the inversion because the ray paths bend around the low-velocity body. The 2008 data also recorded a secondary arrival that may be a delayed P-wave interacting with the low-velocity body.
Committee in charge: Emilie E.E. Hooft, Chairperson; Douglas R. Toomey, Member; Katharine V. Cashman, Member
7
Jolis, Ester M. "Magma-Crust Interaction at Subduction Zone Volcanoes". Doctoral thesis, Uppsala universitet, Berggrundsgeologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-198085.
Testo completoAbstract (sommario):
The focus of this work is magma-crust interaction processes and associated crustal volatile release in subduction zone volcanoes, drawing on rock, mineral, and gas geochemistry as well as experimental petrology. Understanding the multitude of differentiation processes that modify an original magma during ascent to the surface is vital to unravel the contributions of the various sources that contribute to the final magmas erupted at volcanoes. In particular, magma-crust interaction (MCI) processes have been investigated at a variety of scales, from a local scale in the Vesuvius, Merapi, and Kelut studies, to a regional scale, in the Java to Bali segment of the Sunda Arc. The role of crustal influences is still not well constrained in subduction systems, particulary in terms of the compositional impact of direct magma crust interplay. To address this shortcoming, we studied marble and calc-silicate (skarn) xenoliths, and used high resolution short timescale experimental petrology at Vesuvius volcano. The marbles and calc-silicates help to identify different mechanisms of magma-carbonate and magma-xenolith interaction, and the subsequent effects of volatile release on potential eruptive behaviour, while sequential short-duration experiments simulate the actual processes of carbonate assimilation employing natural materials and controlled magmatic conditions. The experiments highlight the efficiency of carbonate assimilation and associated carbonate-derived CO2 liberated over short timescales. The findings at Merapi and Kelut demonstrate a complex magmatic plumbing system underneath these volcanoes with magma residing at different depths, spanning from the mantle-crust boundary to the upper crust. The erupted products and volcanic gas emissions enable us to shed light on MCI-processes and associated volatile release in these systems. The knowledge gained from studying individual volcanoes (e.g., Merapi and Kelut) is then tested on a regional scale and applied to the entire Java and Bali arc segment. An attempt is presented to distinguish the extent of source versus crustal influences and establish a quantitative model of late stage crustal influence in this arc segment. This thesis therefore hopes to contribute to our knowledge of magma genesis and magma-crust interaction (MCI) processes that likely operate in subduction zone systems worldwide.
8
Palma, Lizana José Luis. "Degassing of open-vent low-silica volcanoes". Thesis, Open University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499458.
Testo completoAbstract (sommario):
Open-vent activity at volcanoes of low-silica composition, such as Stromboli (Italy), Villarrica (Chile), Mt. Erebus (Antarctica), Masaya (Nicaragua), is characterised by persistent passive gas emission and recurrent mild explosive outgassing. Four styles of bubble bursting activity have been recognised in such volcanoes: seething magma, small short-lived lava fountains, strombolian explosions and gas puffing. Whilst strombolian explosions are perhaps the most common among these volcanoes, seething magma and small lava fountains have been observed only at the surface of active lava lakes. At Villarrica, one of the two case study volcanoes of this thesis, seething magma consists of continual bursts of bubbles up to a few meters in diameter, with varying strength over the entire surface of the lava lake. Small lava fountains, seen as a vigorous extension of seething magma, commonly lasts 20-120 s and reach 10-40 m high above the lava free-surface. Strombolian explosions exhibit a wide range of behaviour. For instance, they can last for less than a second in a single bubble burst that erupts mainly bombs, as seen at the lava lake of Mt. Erebus and Villarrica volcanoes, or for more than 30 seconds accompanied by large amounts of ash, as seen at Stromboli and Mt. Etna volcanoes. At Stromboli, the second case study volcano, gas puffing consists of small but repetitive bubble bursts with a generally table eruption frequency in the range 0.2-1.2 s⁻¹. More vigorous explosive phenomena, such as hundreds-metres high lava fountains or very strong (paroxysmal) explosions, may occur during eruptions or episodes of elevated activity. Multi-parameter monitoring offers a fuller recognition and understanding of the processes governing the volcanic activity at this type of volcano. For instance, correlations between seismicity and visual observations at Villarrica volcano indicate that the seismic tremor is mostly caused by explosive outgassing.
9
Allen, Daniel R. "Temperature and Variability of Three Ionian Volcanoes". BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2591.
Testo completoAbstract (sommario):
Cassini spacecraft images of Io obtained during its flyby of Jupiter in late 2000 and early 2001 were used to determine the lava composition and eruption style of three faint hotspots, Pillan, Wayland, and Loki. We found a maximum color temperature of 1130+/-289 K for Pillan and maximum color temperatures of 1297+/-289 K and 1387+/-287 K for Wayland and Loki, respectively. These temperatures are suggestive of basaltic lava. The temperatures with the best signal-to-noise ratios also suggested basaltic lava and were found to be 780+/-189 K, 1116+/-250 K, and 1017+/-177 K for Pillan, Wayland, and Loki, respectively. Pillan showed increased activity on the third eclipse day after being fairly constant for the first two days, suggesting increased fountaining or lava flow activity on the third day. The data also suggest that Pillan is surrounded by topography that blocked emission on day000 and caused a much more dramatic decrease in emission. Wayland's intensity decreased over the three eclipses, consistent with a cooling lava flow or decreasing eruption. However, rapid decreases in intensity over periods of 26 to 48 minutes could have resulted from the eruption of highly exposed lava, perhaps an open channel or fountain. The data also suggest Wayland may be in a depression surrounded by ridges that blocked part of the emission. Intensities at Loki over the course of the observation varied in both directions, and were consistent with previous determinations of an often quiescent lava lake with periods of active overturning and fountains.
10
Woog, Friederike. "Ecology and behavior of reintroduced Hawaiian geese". [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=959320423.
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11
Garrison, Jennifer Marie. "Magmatic processes at Cotopaxi Volcano, Ecuador geochemical and petrological constraints and interferences for continental arc volcanoes /". Diss., Restricted to subscribing institutions, 2004. http://proquest.umi.com/pqdweb?did=795958281&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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12
Roberts, Nick Stuart. "Earthquake distributions at volcanoes : models and field observations". Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/23653.
Testo completoAbstract (sommario):
Volcanic earthquakes can provide significant insight into physical processes acting at volcanoes, such as magma accumulation and the mechanisms of deformation of the volcanic edifice. At the same time a statistical analyses of volcanic seismicity prior to an eruption (for example variations in the Gutenberg-Richter b-value – a measure of the proportion of large and small events) are a key component of the practical problem of forecasting eruptions. This thesis aims to tackle two key areas of research that are closely related to these important overall goals, by comparing seismic data obtained from currently-active volcanoes with direct field observation of faulting and fracturing from an exhumed extinct volcano. First I introduce a new approach that improves the accuracy and reliability of calculating spatial and temporal variations of the seismic b-value for frequency-magnitude distributions at active volcanoes, and apply it to several test cases. An extensive literature review highlights a large variability and lack of standardisation of methodology used to analyse frequency-magnitude distributions in the past. Motivated by this, I introduce and test a new workflow to standardise calculating completeness magnitudes of seismic catalogues. The review also highlights the fact that uncertainties in estimating the threshold magnitude of complete reporting have been ignored to date. Here I use synthetic catalogues to quantify this previously unidentified source of error, and provide a template to estimate the total error in b-value. In standard analysis it is also common to sample time windows subjectively, although this can introduce bias. Here I develop a new objective, iterative sampling method that calculates the b-value as a full probability density function which need not have a Gaussian error structure. Application of this method reveals ‘mode-switching’ behaviour for the first time in volcanic seismic catalogues. The results also show b-values often do have a value indistinguishable from that of tectonic seismicity (b=1 within error). Nevertheless there are also several robust examples of real high b-values, as high as 3.3. The second part of the study is based on a field campaign to investigate the fracture zones from an exhumed volcanic setting on the Isle of Rum, NW Scotland. Lithological and structural mapping is used to collect structural data that is then used to quantify and explain complex fracture patterns and the underlying intra-magma chamber processes that occurred there in the geological past. In particular I identify a singular collapse event within the youngest volcanic unit, the Central Intrusion. This is responsible for forming the observed igneous breccias and the lineaments on satellite images that I interpret as contemporaneous faults. Using appropriate scaling relations, I infer the b-value for the Rum lineaments data. This would have been relatively high, at a value of approximately 1.9. The final part of the study compares the fracture data on Rum to earthquake distributions at El Hierro volcano, Canary Islands. Here I show the level of fractal clustering is similar in both an extinct (60 Ma) and a currently active volcano. Both show similar high levels of clustering. However, in both cases there is a difference between the capacity and correlation dimensions (D₀≠D₂), implying the set of rupture sources or mapped fault traces form a multi-fractal set. Broadly, the scaling of fracture sets in an ancient volcano has similar properties to those observed in a modern volcano, except that the Rum data imply a greater absolute degree of spatial clustering of deformation than that for the recent unrest at El Hierro.
13
Llewellyn, Huw Richard. "Facies modelling of a low angle shield volcano and associated extrusive volcanics within the North Atlantic Igneous Province". Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=230048.
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14
Davies, Mark Andrew. "Application of gravity techniques to volcanic studies". Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251382.
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15
Jones, Joshua Robert. "Investigating volcano tectonic interactions in the Natron Rift of the East African Rift System". Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103780.
Testo completoAbstract (sommario):
Continental rifting, like other plate tectonic processes, plays a large role in shaping the Earth's crust. Active rift zones evolve from repeated tectonic and magmatic events including volcanic activity. Through investigations of currently and previously active rifts, scientists have discovered considerable interactions between these tectonic and magmatic processes during a rift's evolution; however questions remain about these interactions especially in youthful stages of rifts. We investigate an early phase magma-rich section of the East African Rift System (EARS), named the Eastern Branch to assess volcano-tectonic interactions. The Eastern Branch of the EARS consists of volcanically rich rifts that are actively spreading the Nubian Plate, Somalian plates, and Victoria block at different evolutionary stages making it an ideal study area for volcano-tectonic interactions. Our initial investigation of active volcano-tectonic interactions centered on a rifting event that occurred between 2007-2008 in the Natron Rift, a rift segment in the southern Eastern Branch located in Northern Tanzania. This rifting event contained multiple occurrences of tectonic, magmatic, and volcanic activity in close proximity. We examine the stress transferred from these events to the Natron Fault, which is the major border fault in the area, with analytical modeling using the USGS program Coulomb 3.4. We processed Global Positioning System (GPS) data that recorded slip on the major border fault in the region in early January 2008 and test which events could generate large enough stress changes to trigger the observed slip using a previously defined threshold of 0.1 MPa. These initial models were created using simplified
model parameters, such as an elastic homogeneous half-space, and find that 1) magmatically induced stress perturbations have the potential to trigger fault slip on rift border faults, 2) magmatic events have the potential to trigger strike‐slip motions on a rift border fault, and 3) the proximity of magmatic activity may affect occurrences of slip on adjacent border faults. We then further investigate volcano-tectonic interactions in the Natron Rift by testing using numerical modeling with the CIG finite element code PyLith. We systematically test how adding topography, heterogeneous materials, and various reservoir volumes to a deflating 3 km deep magma reservoir system at the active volcano Ol Doinyo Lengai can affect stress transfer to the adjacent Natron Fault. We compare eight models with variations in topography, material properties, and reservoir volumes to calculate the percent differences between the models; to test their effects on the stress change results. We find that topography plays the largest role with the effect increasing with reservoir size. Finally, we seek to improve the capability of investigating volcano-tectonic interactions in the Natron Rift at faster time- scales by improving Global Navigation Satellite System (GNSS) positioning data (latitude, longitude, and height) collection and distribution capabilities. In the final part of this work, we describe a new Python-based data broker application, GNSS2CHORDS, that can stream real-time centimeter precision displacement data distributed by UNAVCO real-time GNSS data services to an online EarthCube cybertool called CHORDS. GNSS2CHORDS is applied to the TZVOLCANO GNSS network that monitors Ol Doinyo Lengai in the Natron Rift and its interactions with the adjacent rift border fault, the Natron Fault. This new tool provides a mechanism for assessing volcano-tectonic interactions in real-time. In summary, this work provides a new avenue for understanding volcano-tectonic interactions at unprecedented, 1-second time-scales, demonstrates slip can be triggered by small stress changes from magmatic events during early phase rifting, and provides insights into the key role of volcanic topography during volcano-tectonic interactions.Doctor of Philosophy
Investigating interactions between active volcanoes and tectonics (fault zones) is important for understanding how continental rifts grow and evolve over time. Modern researchers use geodetic data, geologic models, and computer simulations of rift processes; like volcanic eruptions and fault movement; to understand how stress in transferred and material deforms due to rift activity. We are especially interested in understanding the stress interactions when volcanic eruptions and earthquakes happen together over a short time period. Our projects apply these tools to examine a segment of the largest active continental rift zone, the Natron Rift in the East African Rift System (EARS), to understand more about the details of these volcano-tectonic interactions when continents break apart (rifting). We first present results that stress transferred to the Natron Fault associated with magmatic activity from the volcano Ol Doinyo Lengai may trigger a major fault to move. Next, we continue our investigations into volcano-tectonic interactions by seeing how volcanic properties could affect stress transferred in the Natron Rift region. We choose to initially test stress variations associated with different 1) topography surfaces, 2) material properties, and 3) reservoir volumes associated with the volcano Ol Doinyo Lengai using a more advanced computer modeling approach. This deeper investigation provides information about the individual roles these parameters play in a younger rift region. We present results that topography has the most influence on the stress transferred to the Natron Fault in our models, and that the other parameters did not play a large role in influencing the stress transferred. Finally we work to increase the ability for researchers to perform geodetic studies in the Natron Rift by providing a new method to share surface displacement data at an unprecedented 1 position a second rate (near real-time). This new method is a data broker application called GNSS2CHORDS that can stream cm precision displacement data to an online cybertool called CHORDS. With our models and data provided through open source methods this work contributes significantly to our understanding of volcano-tectonic interactions.
16
Fournier, Nicolas. "Shallow volcanic processes at persistently active volcanoes : evidence from a multidisciplinary study at PoaÌs volcano, Costa Rica". Thesis, Open University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411251.
Testo completo
17
Mahony, Susan Helen. "The spatial and temporal distribution of volcanoes in Japan". Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505756.
Testo completoAbstract (sommario):
Japan is located on the westem edge of the Pacific plate, in one of the most dynamic areas on Earth, with approximately 80 active volcanoes and considerable tectonic activity. The Japanese Nuclear Waste Management Organisation (NUMO) will construct a deep geological repository for high level nuclear waste somewhere in Japan. Potential hazard posed by a new volcanic event occurring and disrupting this facility during its operational lifetime need to be thoroughly assessed.
18
Rowlands, Daniel. "Seismic investigations of active volcanoes in extensional tectonic settings". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436641.
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19
Spampinato, Letizia. "Thermal monitoring of active volcanoes using portable infrared imagers". Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609816.
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20
Bredemeyer, Stefan [Verfasser]. "Monitoring gas emissions of active volcanoes - identification of natural degassing variations and combination of volcano monitoring techniques / Stefan Bredemeyer". Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/112814932X/34.
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21
Sawyer, Nuni-Lyn E. "Systematic geochemical and eruptive relations in the late stage evolution of volcanoes from the Hawaiian plume : with case studies of Waianae and East Molokai volcanoes /". Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/6704.
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22
Daniels, Katherine Anne. "Modelling magma transport : a study of dyke injection". Thesis, University of Bristol, 2013. http://hdl.handle.net/1983/b32d1ddc-a0ae-437e-8d7c-11d08c2cc72f.
Testo completoAbstract (sommario):
Dyke injection transports large volumes of magma over great distances, controlling the supply of magma to volcanoes and effectively releasing tensional stress at divergent plate margins. This thesis aims to improve understanding of dyke injection processes on different scales. Dyke shapes measured on the Isle of Rum have been analysed and show a mismatch between the currently accepted theory used to describe their shape, and the measured data. The measured dykes show wider edges than expected, consistent with wedging and cooling of magma in the dyke tips; wedged dykes can act as conduits for longer. Finite difference one- and two-dimensional models for the thermal evolution of the crust due to heat transfer from multiple dyke injection have been developed and applied to the geological setting of the actively spreading Main Ethiopian and Red Sea rifts, where the spreading rates are 5 and 16 mm yr-1 respectively. The model has shown that the spreading rate is the first order control on the temperature build up. Differences in crustal thickness exist between these two regions; the crust has thinned under the Red Sea Rift whilst under the Main Ethiopian Rift there has been no appreciable thinning. This difference has led to the conclusion that the spreading rate, and thus the temperature profile, is the principal cause for the differences in crustal thicknesses. Above the brittle-ductile transition temperature, the crust is likely to undergo pre- dominantly ductile deformation; for slow spreading rates (e.g. 5 mm yr-1), it takes up to 142 ka for the dyke injection site to reach this temperature. The position of the locus of strain at an actively rifting margin migrates with time. For slow spreading rates, the strain locus must remain fixed for at least 142 ka before appreciable crustal heating allows the onset of ductile stretching. Where the spreading rate is faster, the locus of strain must remain fixed for shorter lengths of time. Thus Ethiopia's evolving locus of strain and low spreading rate have likely caused much of the extension to be accommodated by magmatic intrusion rather than by stretching. Comparisons between the thermal model results and geophysical observations from a segment of the Red Sea rift have been made. The mag- netotelluric survey across the rift axis of the actively spreading Red Sea Rift segment has shown two bodies of hot material; one explanation is that the rift axis has jumped. Scaled experimental models have been used to study multiple dyke injection in an extensional tectonic setting. For a fixed overpressure, larger spacings between injections give smaller rotation angles between injections. This is consistent with the rotation angles and injection spacings observed between the recent dyke injections on the Red Sea Rift.
23
Moore, Lowell. "The volatile contents of melt inclusions and implications for mantle degassing and ocean island evolution". Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/93345.
Testo completoAbstract (sommario):
The amount of volatile elements dissolved in silicate melts is a controlling factor in a range of geologic processes, which include hazardous volcanic eruptions, economically-significant ore-forming systems, and global-scale volatile fluxes, which contribute to planetary evolution. While melt volatile contents are important, estimating the origin and fate of volatiles distributed within magmas is challenging because volatiles exsolve from the melt during eruption and are transferred into the atmosphere. Therefore, the stratigraphic record of volcanic and intrusive deposits does not contain direct information regarding the pre-eruptive volatile content of the melt. However, melt inclusions trapped within growing phenocrysts present an opportunity to sample the melt before it has completely degassed. Analysis of melt inclusions is challenging owing to a range of processes which occur after the melt inclusion is trapped and which overprint the original texture and composition of the inclusion at the time of entrapment. Thus, efforts to accurately determine the current composition of the melt inclusion sample and then infer the original composition of the trapped melt which that inclusion represents require a combination of microanalytical, numerical, and/or experimental methods.
In Chapter 1, we present a pedagogical approach for estimating the processes that affect the CO2 content of a magma from its origin during melting a C-bearing source material to its exsolution into a free fluid phase during crystallization and degassing. In Chapter 2, we explore different experimental, microanalytical, and numerical methods which may be used to estimate the CO2 contents of melt inclusions that contain fluid bubbles and describe the advantages and disadvantages of each approach. In Chapter 3, we apply some of the methods discussed in the previous chapters to estimate the pre-eruptive volatile content of Haleakala Volcano (Maui) and assess different melting mechanisms that may be active in the Hawaiian plume.Doctor of Philosophy
Volcanoes are features which form on the Earth’s surface and are located above regions where material melts tens of kilometers (or more) below the surface. The process of melting is studied through laboratory experimentation, and therefore it is possible to estimate the composition of deep subsurface material based on the compositions of volcanic rocks which can be sampled on the Earth's surface. This sub-discipline of geologic research is called "igneous petrology." A fundamental problem in igneous petrology is estimating the volatile content of the Earth's deep interior. Volatile elements are those elements such as hydrogen and carbon, which are stable as gasses in the atmosphere rather than in the mineral components of a rock. It is thought that the gasses produced from volcanic vents, of which the compositions are well known, represent volatile elements which were originally present as dissolved components in the melt. Experiments performed on volcanic rocks have demonstrated that volatile elements can be dissolved in melts at high pressures corresponding to depths within the Earth's crust, and these elements exsolve from the melt when it approaches the surface -- similar to how CO2 can be dissolved in a carbonated beverage, which bubbles out when the beverage is opened. The only geologically-persistent features which preserves the pre-eruptive volatile content of a melt (i.e. how much gas was dissolved before eruption) are droplets of melt which are accidentally trapped within crystals that grow from the melt as it cools near the Earth's surface -- these are called "melt inclusions." While melt inclusions are useful in this regard, they are challenging to apply to geologic problems because they undergo a range of physical and chemical changes after they are trapped, which can alter their composition from the original composition of the melt that was trapped. This dissertation concerns the theory used to infer how volatile elements are distributed within the deep Earth, analytical and numerical methods used to gather relevant information from melt inclusion samples, and an application of these methods to investigate the volatile content of the mantle below Hawaii. Chapter 1 describes a framework for systematically determining the amount of CO2 distrubuted within a given volcanic setting. Chapter 2 compares different methods used to estimate the original volatile content of melt inclusions from Kamchatka, which have formed fluid bubbles -- a common feature present in melt inclusions. Chapter 3 applies the methods described in the first two chapters to estimate how volatile elements are distributed within the Earth's mantle below Hawaii, and how the process of melting transfers them to the Earth's atmosphere.
24
Witter, Jeffrey Bruce. "Convection of magma in volcanic conduits as a degassing mechanism at active volcanoes /". Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/6721.
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25
Walwer, Damian. "Dynamique non linéaire des systèmes volcaniques à partir des données géodésiques". Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEE004/document.
Testo completoAbstract (sommario):
Nous étudions dans un premier temps l'intérêt de l'utilisation de la "multichannel singular spectrum analysis" (M-SSA) sur des séries temporelles de positionnements GPS. Cette méthode permet de simultanément analyser un ensemble de séries temporelles et d'en extraire des modes de variabilités communs sans utiliser d'information a priori sur les structures spatiales et temporelles des champs géophysiques. Ces modes correspondent à des tendances non linéaires, des oscillations ou du bruit. Nous l'appliquons à des données enregistrées sur le volcan Akutan en Alaska. Nous y extrayons deux types de signaux. L'un correspondant à des déformations dites saisonnières, l'autre représentant deux cycles d'inflations et de déflations successifs du volcan Akutan. Les inflations sont rapides et courtes et suivies de déflations plus lentes et plus longues. Dans une seconde partie nous tirons parti de la M-SSA pour analyser des séries temporelles enregistrées sur plusieurs volcans. Les volcans Okmok et Shishaldin en Alaska et le Piton de la Fournaise à la Réunion possèdent une partie de leurs histoires de déformations qui est similaire à celle d'Akutan. Le caractère oscillatoire de ces cycles de déformations est comparé au régime oscillatoire d'un simple oscillateur non linéaire. Les données pétrologiques, géochimiques et géophysiques disponibles pour Okmok et le Piton de la Fournaise combinées aux contraintes sur la dynamique apportées par l'oscillateur non linéaire permet de proposer un modèle physique. Deux réservoirs superficiels sont connectés par un conduit cylindrique dans lequel le magma possède une viscosité qui dépend de la température. Un tel système se comporte de manière similaire à l'oscillateur non linéaire étudié précédemment. Lorsque que le gradient de température vertical présent dans le fluide est suffisamment important et que le flux de magma entrant dans le système de réservoirs est compris entre deux valeurs déterminées analytiquement un régime oscillatoire se met en placeWe study the use of the "multichannel singular spectrum analysis" on GPS time series. This method allows to simultaneously analyze a set of time series in order to extract from it common modes of variability without using any a priori on the temporal or the spatial structure of geophysical fields. The extracted modes correspond either to nonlinear trends, oscillations or noise. The method is applied on a set of GPS time series recorded at Akutan, a volcano located in Aleutian arc in Alaska. Two types of signals are extracted from it. The first one corresponds to seasonal deformations and the other represents two successive cycles of inflation and subsidence of Akutan volcano. The inflations are fast and short and are followed by deflations that are slower and longer. In the second part we take benefit of the M-SSA to analyze GPS time series recorded at several volcanoes. Okmok and Shishaldin in Alaska and Piton de la Fournaise in La Réunion possess a part of their deformation history that is similar to Akutan volcano. The cyclic nature of the observed deformations leads us to make an analogy between the oscillatory regime of a simple nonlinear oscillator and the deformation cycles of these volcanoes. Geochemical, petrological and geophysical data available for Okmok and Piton de la Fournaise combined with the constraint on the qualitative dynamics bring by the nonlinear oscillator allow to propose a physical model. Two shallow reservoirs are connected by a cylindrical conduit in which the magma have a viscosity that depends on the temperature. Such system behaves like the nonlinear oscillator mentioned above. When the temperature gradient inside theconduit is large enough and the flux of magma entering the shallow system is bounded by values that are determined analytically anonlinear oscillatory regime arises
26
Stone, Jonathan. "The roles of participatory monitoring in reducing risk around volcanoes". Thesis, University of East Anglia, 2015. https://ueaeprints.uea.ac.uk/61697/.
Testo completoAbstract (sommario):
This thesis examines the roles of participatory monitoring in reducing disaster risk around volcanoes, by the production of knowledge, enhancing the provision of early warnings, and stimulating risk reducing adaptations. Citizen participation in processes that manage and reduce risk is thought to be essential for building resilient and sustainable development. This thesis addresses gaps in theoretical and practical understanding of the roles of citizens in the production and use of knowledge through participatory monitoring, and the roles of participatory monitoring in reducing risk. Findings are presented from a global survey of citizen participation with volcano monitoring institutions, comparing across different volcanic, cultural, and risk governance settings. It describes how many of the institutions’ motivations are focused on knowledge production and relational trust benefits, but that most initiatives are ad-hoc and reactive to eruptive events, and thus unlikely to quite deliver the expected benefits. Using an in depth case-study on risk reduction through a community-based monitoring network around volcán Tungurahua, Ecuador, the roles of participatory monitoring at a community scale are analysed. The network grew organically and has multiple risk reduction roles through knowledge production, early warning, enhanced risk awareness, fostering trust-based relationships between scientists and communities, facilitating risk reducing adaptations at community and district levels to multiple hazards. The contextual influences on participatory monitoring are identified using in depth case-studies of participatory monitoring through long-lived eruptions at two volcanoes: Soufrière Hills Volcano, Montserrat; and volcán Tungurahua. Findings show the importance of the risk context, how risk is managed, the ways that monitoring institutions learn, and the effect of these influences on each other and on the agency of citizens. The thesis demonstrates that participatory monitoring and participating citizens can have multiple risk reducing roles through knowledge production, knowledge communication, and the actions that can be taken based on knowledge.
27
Yassir, Najwa A. "Mud volcanoes and the behaviour of overpressured clays and silts". Thesis, University College London (University of London), 1989. http://discovery.ucl.ac.uk/1349596/.
Testo completoAbstract (sommario):
Mud volcanoes are a poorly understood phenomenon whereby overpressured, fine-grained sediments extrude to the surface from depths of up to several kilometres. They are observed worldwide, usually in areas of tectonic compression and thick, rapidly-deposited sedimentary sequences. This research is aimed at achieving a better understanding of the type of sediment behaviour leading to mud volcanoes. The study combines a geological investigation of the origin of mud volcanoes with a geotechnical investigation of their behaviour. As part of the geological study, the mud volcano examples around the world are described, and possible mechanisms of overpressuring and extrusion are investigated. Particular attention is paid to the field description and the subsurface geology of the mud volcano areas visited in South Trinidad and Southwest Taiwan. The results of laboratory analyses on the muds sampled in the field, mineralogy, particle size and shapes, Atterberg limits and, where possible, micropalaeontology, are presented. These are aimed at understanding the origin of the clay and establishing any characteristics unique to mud volcanoes. The geotechnical investigation concentrates on the undrained shear behaviour of mud volcano clays, which originate in an environment where thick, low permeability sedimentary sequences are subjected to tectonic compression. The experiments were conducted in a high pressure triaxial cell, using confining pressures of 5 to 50 MPa. Particular attention is paid to the effects of consolidation path, stress magnitude and material properties on the behaviour of mud volcano clays. The results of the experiments are discussed in the light of the geological study, and equivalent testing results from low pressure soil mechanics studies. The discussion concentrates on the role of tectonic activity in the formation of mud volcanoes.
28
Harris, Andrew John Lang. "Thermal monitoring of volcanoes from space at low spatial resolution". Thesis, Open University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309863.
Testo completo
29
Hornby, A. J. "Fracture, friction and fragmentation : brittle processes at lava dome volcanoes". Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3005862/.
Testo completoAbstract (sommario):
The extent to which transitions from dominantly viscous to dominantly brittle magma deformation regulate eruptive activity has not been widely explored in volcanology. Within this thesis, investigations combining experiments, petrology and geophysical signals are presented to help decipher and understand the role of brittle deformation during lava dome eruptions. Lava domes are commonly associated with explosions and dome collapse events, both of which generate volcanic ash. In order to recognise and discriminate fragmentation mechanisms from ash samples, the physical properties and mineralogy of natural ash produced during a typical Vulcanian explosion and a dome collapse event were compared. Measurements of the componentry of several thousand ash particles were conducted using QEMSCAN® Particle Mineralogical Analysis, a rapid automated SEM-EDS mapping technique. Analysis of images obtained by QEMSCAN® reveals that the relative distribution of plagioclase and glass present along the ash particle boundaries varied for both generation mechanisms. Deconvolution of particle size distributions and particle shape analyses shows that ash ejected in Vulcanian explosions has a more complex fragmentation and transport history, while ash produced in pyroclastic flows shows the dominance of a single process. These results suggest mechanism-dependent controls on the surface composition and componentry of volcanic ash – future work is required to discriminate fragmentation mechanisms from ash characteristics through the use of QEMSCAN® data. Explosive fragmentation at lava dome volcanoes is likely to be triggered by tensile failure of magma following stress accumulation. In order to investigate pressure-driven fracturing of conduit magma, Brazilian tensile tests were conducted on lava samples from Santiaguito volcano at ambient and magmatic temperatures. These tests reveal that deformation style becomes sensitive to small changes in temperature and strain rate at temperatures of 750-800 °C. Higher temperatures generated increasingly viscous deformation, while faster strain rates promoted more brittle behaviour. Experimental constraints on the strain rate and strain leading to failure can be compared to natural deformation timescales recorded in cycles of inflation preceding explosions at Santiaguito, which shows that a viscous component accompanies deformation and suggests that fractures propagate away from a pressure source prior to explosive eruption. Following fracture propagation, any remaining energy is likely to be accommodated by fault slip along the fracture plane. These faulting events are investigated using a high-velocity rotary shear apparatus, showing that the response to faulting generates temperatures sufficient to produce frictional melt within ~10 cm of slip under the slip rates and normal stresses constrained through monitoring of the volcanic behaviour at Santiaguito. The range of mechanical response to slip events in the volcanic conduit and their relation to concurrent seismic signals are investigated in greater detail during the extrusion of a lava spine at Mt Unzen (Japan). Examination of textures at the spine margins and similarity of the seismic signals that accompanied its extrusion has determined that spine emplacement proceeds by incremental fault slip events in the shallow edifice. Waveform analysis together with spine growth observations allow calculation of the average slip distance (8.9 cm) and slip velocity (0.75 m.s-1). These calculations are combined with results from laboratory measurements in a high-velocity rotary shear apparatus to define the range of depths where average faulting events would induce viscous remobilisation (at >275m) and frictional melting along the fault plane (at >500 m). The frictional properties of the dome rocks and the viscosity of the frictional melt in the fault zone suggest that at shallow depths frictional melts act as a viscous brake to fault slip, potentially augmenting stick-slip spine growth. Taken together, the failure, faulting and fragmentation of dome-forming magma demonstrates that our interpretation of eruptive activity at lava dome volcanoes requires a fundamental understanding of brittle processes.
30
Salem, Lois Claire. "Magmatic processes at basaltic volcanoes : insights from the crystal cargo". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277726.
Testo completoAbstract (sommario):
A plethora of magmatic processing occurs in magma reservoirs, where melts are stored prior to eruption. Magma reservoirs are complex, open systems, and often multiple reservoirs are partially inter-connected from source to surface, giving rise to the term 'volcanic plumbing system'. Parental melts feeding these reservoirs can have diverse and distinct geochemical and petrological characteristics, and be variably evolved or enriched. These melts can also bring with them a crystal cargo that may remain in equilibrium in the magma reservoir, but may also be modified by reaction, resorption, crystallisation and diffusion. Melts and crystals can be transported between reservoirs, from the upper mantle and through the crust, leading to melt mixing, reactions and volatile exsolution. Basaltic volcanic systems are fed by primitive melts, and due to the rapid ascent of melts and short magma storage times, these volcanoes provide the best means of unravelling the mantle and crustal contribution to geochemical heterogeneity observed in erupted samples. Despite the potential chemical complexity of a magma reservoir, evidence for magma processing and reaction can be preserved in melt inclusion suites and the compositional structure of their host crystals. Magmatic processes during storage and transport at two basaltic volcanoes are investigated using two carefully selected eruptions: the 1669 eruption at Mt. Etna, and the 2007 Father's Day eruption at Kīlauea. A suite of diverse geochemical, petrological and petrographical observations, made at a range of length-scales, are combined and interpreted in tandem with geophysical monitoring data. The conclusions of these studies shed light on the architecture of each volcano's plumbing systems and basaltic plumbing systems in general. This thesis is divided into two parts. The first study unravels the crustal and mantle processes controlling melt geochemical heterogeneity at Mt. Etna, Sicily, during the 1669 eruption, the largest eruption in historical times. The 1669 melt inclusion suite arises from the mixing of two basaltic melts with similar major element compositions but very different trace and volatile element compositions. The melt geochemistry suggests that at least one end-member melt has been heavily influenced by assimilation of carbonate in the crust. The elevation in alkalis, caused by carbonate assimilation, enhances carbon and sulfur solubility in one end member. The melt inclusion suite indicates that mixing of these melts occurred in the shallow crust shortly before eruption and this mixing may be the cause of the enhanced $CO_{2}$ fluxes prior to eruptions at Mt. Etna. The second study is split into two parts. Each uses the eruptive products of the Father's Day eruption at Kīlauea and aims to unravel the connectivity of the plumbing system between the summit and East Rift Zone, with a focus on timescales of storage and transport. The first part investigates the melt geochemistry in terms of heterogeneity and volatile composition, and the second investigates the crystal cargo in terms of features of the macro-scale crystal cargo distribution and the micro-scale geochemical zoning of individual crystals. The integration of observations and models from these two studies constrains the pressure, temperature and composition of source magma feeding the Father's Day eruption. The eruption is investigated in the context of the "magma surge'' event that preceded the intrusion, as well as within the context of the longer-term trends in Kīlauea geochemistry at the summit and East Rift Zone. Melt inclusion and matrix glass volatile systematics provide insights into the degassing path of the magma and the duration of magma transport to the surface is constrained by diffusion modelling. Estimated timescales for ascent by diffusion modelling of macrocryst major element composition, melt inclusion water content and the melt Fe$^{3+}$/Fe$_{tot}$ ratio are in agreement with timescales observed from the geophysical data of $< $8 hours from reservoir depth to eruption. Both studies emphasise how petrological observations can supplement geophysical monitoring datasets collected at the surface to aid our interpretation of volcanic behaviour and eruption forecasting.
31
Zoghbi, Christiane A. (Christiane Antoine). "Rural groundwater supply for the Volcanoes National Park region, Rwanda". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39272.
Testo completoAbstract (sommario):
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.Includes bibliographical references (leaves 81-83).
Water scarcity is a major issue faced by both developed and developing countries. According to the Millennium Development Goals set by the United Nations, the number of people that do not have access to an improved water supply should be halved by the year 2015. Rwanda is a Sub-Saharan developing country where water scarcity is an issue. This thesis presents results from a preliminary evaluation of possible groundwater supply to the village of Bisate, located in the Northern Province of Rwanda. Suffering from the "walk for water", the Bisate community has to give up vital activities such as school and agriculture in order to fetch water. During the dry season, the people are obliged to go into the Volcanoes National Park to get water from springs and swamps, disrupting the fragile ecosystem by the human activity. All these factors make it important to provide water at the point of use. Since the region receives a considerable amount of rain and the groundwater recharge rate is high (0.3 m/year), groundwater supply could be a feasible alternative for the Bisate community. For this thesis, three major tasks were achieved.
(cont.) First, a description of the park's hydrogeology was developed based on previous studies and field observations. Second, a calculation of the groundwater recharge using the Water Balance Method was completed. And finally, a groundwater model was built using MODFLOW software. The aim of the model is to estimate the depth to the water table. The model results have shown that the water table could be as deep as 750 meters below the ground surface of quite shallow depending on the model assumptions. According to four trials, each with different boundary conditions and internal properties of the medium, the results were found to depend upon the assumed hydraulic conductivity and the boundary conditions. The strongest conclusion is that field investigations of the groundwater system are needed to determine actual aquifer properties and field conditions.
by Christiane A. Zoghbi.
M.Eng.
32
Alfaro, Raimon. "Seismic studies of active volcanoes under the Vatnajökull icecap, Iceland". Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620170.
Testo completo
33
McNeilage, Alastair John. "Mountain gorillas in the Virunga volcanoes : ecology and carrying capacity". Thesis, University of Bristol, 1995. http://hdl.handle.net/1983/13bb843d-3c07-4c18-838f-15aa71d766b4.
Testo completo
34
Rodrigues, Clara Lúcia Ferreira. "Macrofaunal assemblages from mud volcanoes in the Gulf of Cadiz". Doctoral thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/981.
Testo completoAbstract (sommario):
Doutoramento em BiologiaDesde a descoberta em 1999 do primeiro vulcão de lama no Golfo de Cádis, cerca de 40 locais, de profundidade variável entre os 200 e os 3900 m, com diferentes graus de emissão de hidrocarbonetos foram localizados e amostrados dentro do programa IOC-UNESCO “Training Through Research (TTR) “ e mais recentemente dentro do projecto europeu HERMES. Neste estudo investigamos as comunidades da macrofauna dos vulcões de lama do Golfo de Cádis utilizando uma diversidade de equipamento de amostragem quantitativo e não quantitativo. Mais de 14550 espécimes foram examinados e incluídos nos diferentes grupos taxonómicos, sendo fornecida uma lista taxonómica detalhada com o menor nível taxonómico possível. A biodiversidade, distribuição dos principais taxa, as espécies quimiossintéticas e a biodiversidade regional e substituição de espécies são apresentados e discutidos. Dentro da macrofauna, os bivalves (nomeadamente super-familia Thyasiroidea, espécies quimisimbióticos e comunidade de bivalves) e os ofiurideos são estudados em pormenor. Os Thyasiroidea colhidos nos vulcões de lama do Golfo de Cádis são revistos. Das sete espécies identificadas, apenas uma Thyasira vulcolutre. sp. nov se encontra associada a um ambiente quimiossintético. Esta espécie é restrita a locais activos, mas não se verificam padrões de distribuição para as outras espécies. Os bivalves quimiosimbióticos amostrados são revistos. Das 10 espécies fortemente associadas a ambientes quimiossintéticos duas Solemyidae, Petrasma elarraichensis sp. nov. e Acharax gadirae sp. nov., uma Lucinidae, Lucinoma asapheus sp. nov., e uma Vesicomyidae, Isorropodon megadesmus sp. nov. são descritas e comparadas com similares das respectivas famílias. As comunidades de bivalves foram analisadas em detalhe e do estudo de 759 espécimes (49 espécies em 21 familias) descreve-se a diversidade e padrões de distribuição. Os Ophiuroidea amostrados nos vulcões de lama e ambientes batiais adjacentes são revistos. Treze espécies são incluídas em 4 famílias, Ophiacanthidae, Ophiactidae, Amphiuridae e Ophiuridae e são identificadas, tendo sido descrita uma nova espécie Ophiopristis cadiza sp. nov. Rácios isotópicos (δ13C, δ15N, δ34S) foram determinados em várias espécies no intuito de investigar a ecologia trófica das comunidades bênticas dos vulcões do Golfo de Cádis. Os valores de δ13C para os bivalves Solemyidae, Lucinidae e Thyasiridae estão de acordo com os valores para outros bivalves conhecidos por possuírem simbiontes tiotróficos. Por outro lado os valores de δ13C e δ34S para Bathymodiolus mauritanicus sugerem a ocorrência de metanotrofia. A análise da fauna heterotrófica indica igualmente que as espécies habitantes da cratera dos vulcões de lama derivam a sua nutrição de fontes quimiossintéticas. A indicação pela análise isotópica que as bactérias autotróficas contribuem substancialmente para a nutrição dos bivalves hospedeiros, levou-nos a investigar os endossimbiontes e as suas relações filogenéticas relativamente a outros bivalves através da análise comparativa de análises de sequências de 16S ribossomal RNS. Análises moleculares PCR-DGGE (Denaturing Gradient Gel Electrophoresis) e clonagem de genes de bacterias 16S rRNA confirmaram a presença de simbiontes oxidantes de enxofre e colocam a possibilidade de uma simbiose dupla para o B. mauritanicus. A diversidade microbiana dentro dos Frenulata foi igualmente estudada recorrendo a métodos moleculares e revelou a não existência de padrão entre espécies, vulcões, profundidade e idade do animal sugerindo assim a não procura de simbiontes específicos.
Since the discovery in 1999 of the first mud volcano in the Gulf of Cadiz, about 40 other sites at depths ranging from 200 to 3900m, with varying degrees of hydrocarbon-rich gas seepage activity, have been located and sampled under the IOC-UNESCO Training Through Research (TTR) programme and, more recently, the EU funded HERMES project. In this study we investigate the macrofaunal assemblages from mud volcanoes in the Gulf of Cadiz using a diverse array of quantitative and non-quantitative sampling gear. More than 14550 specimens were examined and ascribed to different taxonomic groups and a detailed taxonomic list with the lowest possible taxonomic level possible at the moment is provided. The biodiversity and distribution of major taxa, the chemosymbiotic species and the regional biodiversity and species turnover are present and discussed. Within macrofauna, bivalves (namely the super-family Thyasiroidea, chemosymbiotic species and bivalves assemblages) and ophiuroids were studied in detail. Thyasiroidea collected from the mud volcanoes of the Gulf of Cadiz are reviewed. Of the seven species identified only one, Thyasira vulcolutre. sp. nov, is closely associated with a chemosynthetic setting. Thyasira vulcolutre is restricted to active seeps but there is no pattern in the distribution of the other thyasirid species. The chemosymbiotic bivalves collected are reviewed. Of the ten species closely associated with chemosynthetic settings two Solemyidae, Petrasma elarraichensis sp. nov. and Acharax gadirae sp. nov., one Lucinidae, Lucinoma asapheus sp. nov., and one Vesicomyidae, Isorropodon megadesmus sp. nov. are described and compared to close relatives of their respective families. The deep-water bivalve assemblages were also analyzed in detail. From the study of 759 specimens representing 49 species in 21 families, the diversity, distribution patterns and species turnover are described. The Ophiuroidea collected from mud volcanoes and adjacent bathyal environments from the Gulf of Cadiz are reviewed. Thirteen species included in four families, Ophiacanthidae, Ophiactidae, Amphiuridae and Ophiuridae were identified and one new species Ophiopristis cadiza sp. nov was described. Stable isotopes ratios (δ13C, δ15N, δ34S) were determined in several species to investigate the trophic ecology of the benthic assemblages from mud volcanoes in the Gulf of Cadiz. The δ13C values for solemyid, lucinid and thyasirid bivalves are in line with data for other bivalves known to host thiotrophic symbionts. On the other hand, δ13C and δ34S values for the bathymodiolid species are compatible with the predominance of methanotrophy. The analyses of heterotrophic fauna indicate that the species inhabiting the crater of the mud volcanoes derive the bulk of their nutrition from chemoautolithotrophic sources. The indication by stable isotope analysis that autotrophic bacteria make a substantial contribution to the nutrition of the bivalve hosts, led us to investigate the bacterial endosymbionts and their phylogenetic relationship to other symbionts in bivalve hosts based on comparative 16S ribosomal RNA gene sequence analysis. Molecular analysis using PCR-DGGE (Denaturing Gradient Gel Electrophoresis) and cloning of bacterial 16S rRNA genes confirmed the presence of sulphur-oxidizing symbionts within gill tissues of the studied bivalve specimens and point out to the possibility of a dual sumbioses for Bathymodiolus mauritanicus The microbial diversity inside frenulata worms was also analyzed using the same molecular tools and revealed no patterns between species, MV, depth, age of animal and therefore seems to suggest that they do not seem to select for specific symbionts.
35
Karl, Sandra. "The source mechanisms of low frequency seismic events on volcanoes". Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/8406/.
Testo completoAbstract (sommario):
Volcanoes generate a variety of seismic signals. One specific type, the so-called low frequency (LF) event, has proven to be crucial for understanding the internal dynamics of the volcanic system. While many endeavours have concentrated on the nature and cause of the seismic coda, the actual trigger mechanism of these events is still poorly understood. Several conceptual source models have been developed, ranging from magma-water interaction, stick-slip motion of magma plugs, magma flow instabilities, repeated release of gas-ash mixtures into open cracks, magma wagging, to brittle fracturing of magma. All but one trigger model, namely brittle failure of magma in the glass transition as response to the upwards movement of magma, fail to explain all observed characteristics of LF volcanic seismicity. Here, a spatially extended source, the ring fault structure, is developed to mimic the proposed source mechanism. The extended LF source is modelled as an arrangement of 8, 16 and 32 double couples (DCs) approximating a 30 m, 50 m and 70 m wide circular ring fault bounding the circumference of the volcanic conduit. Due to (partial) destructive interference, P-wave amplitudes of a ring fault structure are greatly reduced compared to single double couples and compensated linear vector dipoles (CLVDs), by 350% and 470%, respectively. It is shown here that these seismic amplitude differences may result in the underestimation of average slip and thus magma ascent rate by a factor of up to 3.5 when using an over simplified point source. To resolve the driving forces of LFs, synthetic seismograms representing both point and spatially extended sources were inverted for the apparent physical source mechanism using moment tensor inversion techniques (MTI). If original input parameters were unknown, MTI results of the ring fault would indicate a combination of 63% isotropic and 37% CLVD components. The proposed moment tensor strongly resembles that of a real CLVD case. The results of this study give evidence that slip along the conduit walls yields the same MTI results as a subhorizontal tensile crack, and the importance of knowledge about the source nature becomes eminently significant. Spatially extended source geometries describe an alternative to point dislocation sources. Additionally to the ring fault structure, this study provides a catalogue of further complex source scenarios involving new spatially extended sources, such as slip along a dike, conduit segments, two simultaneously acting ring fault structures, and helix-like flow patterns. P-wave amplitudes and waveforms vary largely with source geometry, stressing that source geometry is key for source interpretations and thus it is not sufficient to assume a point source nature of the processes involved to generated the observed seismicity.
36
Stevenson, David Stacey. "Heat transfer in active volcanoes : models of crater lake systems". Thesis, Open University, 1992. http://oro.open.ac.uk/57398/.
Testo completoAbstract (sommario):
Heat transfer in active volcanoes was investigated in this thesis. A general model of a crater lake system was developed that takes inputs of lake temperature, volume, chemical content, and meteorological conditions, and outputs the mass, energy, and chemical flows to and from the lake. The model was applied to lakes at Pods (Costa Rica) and Ruapehu (New Zealand), yielding volcanic power outputs of -102-103 MW, and heat fluxes of -102-104 W m-2. Heat is added to the lakes by hot brine and steam, derived from lake seepage and magmatic gas. The heat source is magma crystallising, cooling, and degassing. Background heat inputs are maintained by hydrothermal infiltration of magma, releasing latent and specific heat. Infiltration of the conductive boundary layer surrounding magma was modelled. The permeability created by contractive cooling was equated with the permeability required for two-phase convection to transport heat away from the boundary. Infiltration rates of -1-100 m a-1 (metres/year), into conductive layers -30-0.3 m thick, creating permeabilities of _10-10-10-14m 2, will provide the required heat flux. Cracking temperatures of magma depend upon infiltration rate, ranging from hydrothermal system temperatures at slow rates, to magma temperatures at the fastest rates. Predicted maximum rates are -300 m a-1 for near-surface magma, and -800 m a-1 for magma at -1-3 km depth. Measured S02 fluxes at Pods, and calculated influxes of HCl to both lakes imply that degassed magma volumes (-0.004-0.08 km3 a-i) are much larger than likely intrusions. A new model was developed of small, vesiculating intrusions that circulate magma due to the density increase associated with gas loss. Dense, degassed magma descends, whilst buoyant, volatile-rich magma rises from a deep source. Pipe-like intrusions of radius -5 m, tapping magma volumes >-0.05 km3, can produce the gas fluxes needed. Intrusions of this type probably occurred in 1980/81 and 1986 at Pods, and in 1968,1971,1975,1977,1981 and 1985 at Ruapehu, and were followed by intermittent eruptions and degassing. This degassing mechanism probably occurs at many volcanoes where high gas fluxes are observed, but no evidence exists for large, shallow intrusions. A model of compressible fluid flow in a rough fumarole conduit, with conductive heat loss to the surroundings, allows fumarole temperatures to be used to estimate the depth of their magma source. This also indicates shallow magma was emplaced at Pods in 1980/81 and 1986. In summary, heat transfer is achieved by a combination of intermittent gas release from minor shallow intrusions, together with infiltration of deeper magma. Infiltration is one mechanism for providing fractures allowing the release of gas from shallow intrusions, and circulation probably ceases due to freezing caused by infiltration.
37
Deardorff, Nicholas D. 1980. "Eruptive Processes of Mafic Arc Volcanoes – Subaerial and Submarine Perspectives". Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11969.
Testo completoAbstract (sommario):
xviii, 179 p. : ill. (some col.). Includes 3 video files.Mafic arc volcanoes have eruption styles that range from explosive to effusive. In a broad sense, eruption style is controlled by the rate of magma supply to the vent. In this dissertation I examine relationships between eruption rate and style in two separate studies: (1) an investigation of ongoing activity at NW Rota-1, a submarine volcano in the Mariana arc, and (2) a morphologic study of the Collier Cone lava flow field in the Central Oregon Cascades. The eruptions of NW Rota-1 range from effusive to moderately explosive; eruptions are effusive when mass eruption rate (MER) is low and explosive when MER increases. The explosivity of submarine eruptions is suppressed by seawater because of increased hydrostatic pressure, rapid cooling, and the high viscosity of water relative to air (which limits expansion). The combination of seawater and relatively low MERs limit pyroclast deposition to within meters to tens of meters of the vent. In fact, many pyroclasts fall back into the vent and are recycled. Evidence for recycling includes microcrystalline inclusions within erupted pyroclasts and elevated Cl and Na concentrations in matrix glass. Enrichment of Cl and Na suggests that seawater assimilation provides a geochemical signature of recycling. Recycling is limited to low MER explosive eruptions and is not observed in either effusive lava or deposits from high MER explosions. Direct observations of eruptions allow measurements of eruption rate. However, it is more challenging to estimate MERs of eruptions that were not observed. To address this problem, I develop and test methods of constraining the eruption rate (and duration) of the c. 1600 year old Collier Cone lava flow using the flow morphology. To quantify flow morphology I combine field observations with GIS analysis of Lidar-derived digital topography. Channel dimensions constrain emplacement rates; dominant wavelengths and amplitudes of surface folds constrain spatial and temporal changes in flow rheology. Three videos of eruption activity accompany this dissertation as supplemental files. This dissertation includes both previously published and unpublished co-authored material.
Committee in charge: Dr. Katharine V. Cashman, Chair; Dr. Joshua J. Roering, Member; Dr. Paul J. Wallace, Member; Dr. Patricia F. McDowell, Outside Member; Dr. William W. Chadwick, Outside Member
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Ohlschlager, Justin George. "Glacier Change on the Three Sisters Volcanoes, Oregon: 1900-2010". PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2448.
Testo completoAbstract (sommario):
A glacier responds to changes in climate by subsequent retreat and advance as a result of changes in snow inputs and outputs. Understanding these changes is important because shrinking glaciers limit and diminish local water resources. They contribute to alpine runoff in the late-summer months by delaying the maximum runoff until late in the melt season. A comprehensive glacier and perennial snowfield inventory has not been completed for the Three Sisters in Central Oregon. Using aerial photography, Digital Elevation Models (DEMs), previous studies, and historical ground based photographs these glacier and perennial snowfields were defined and their surface area change was quantified along with surface area and volume change for the 15 named glaciers for multiple years. The glaciers and perennial snowfields totaled 9.03 ± 1.65 km2 in 1949 and decreased to 7.1 ± 1.16 km2 in 2003 giving a total loss of -1.914 ± 0.974 km2 ( 21%). The 15 named glaciers totaled 12.43 ± 0.417 km2 in ~1900 and decreased to 5.65 ± 0.135 km2 in 2003 giving a total loss of -6.70 ± 0.439 km2 (54%) with more loss occurring in the early part of the century. It's estimated that the 15 named glaciers lost roughly 61% of volume from 1900 to 2010. From 1957 to 2010 their surface's dropped in elevation on average by -8.9m, losing an estimated 71.96 x 106 ± 2.87 x 106 m3 (53%) in total volume, seen across accumulation and ablation zones, with more loss happening from 1957 to 1990. There was no relationship found between topography and area. A small correlation was found between slope and increased volume change. Debris cover on glacier surfaces has increased and showed a correlation between decreasing area loss (no correlation with volume changes).
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Wooten, Rebecca Dyanne. "Statistical environmental models : hurricanes, lightning, rainfall, floods, red tide and volcanoes". [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001824.
Testo completo
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Beckett, F. M. "Exchange flow experiments and implications for degasing processes at basaltic volcanoes". Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.573419.
Testo completoAbstract (sommario):
Persistently active basaltic volcanoes are characterised by Strombolian eruptions that punctuate continuous passive degassing. Persistent passive degassing can be driven by an exchange flow of magma within the conduit. To interpret persistent gas emissions and changes in activity requires some knowledge of the flow regime and an understanding of how its volume flux depends on the physical properties of the magma and the conduit geometry. This thesis presents an experimental study of buoyancy-driven, low Reynolds number, (Re < 6) exchange flow of two Newtonian fluids in a vertical cylindrical pipe over long time durations. Two distinct flow regimes were observed~~ymmetric core annular flow (CAF) and side-by-side (SBS) flow. The flow regime formed was found. to be dependent on the viscosity ratio of the two fluids ((3); CAF occur at (3 2: 100, SBS flow occur at (3 ;S 100. It is shown that fluids are not arranged in the regime that maximises volume flux (e.g. SBS or CAF), nor do they adopt the geometry that maximises volume flux within that particular regime. When the pipe is inclined from the vertical at e > 5° the flow regime is always SBS flow, regardless of (3. The physical and chemical processes driving an exchange flow at Stromboli are con- strained by degassing and crystallisation paths to produce a 3-phase (melt, crystals, bubbles) model of ascending and descending magma driving persistent gas fluxes at Stromboli, assuming a cylindrical pipe geometry. Combining modelled magma prop- erties with the analogue exchange flow experiments the flow regime of magma driving persistent degassing is defined as a function of pressure. At pressures 2: 90 MPa the flow regime is CAF and at pressures ;S 90 MPa the flow regime is SBS flow. Strombolian eruptions are posited to be driven by the ascent and bursting of large gas slugs. The influence of an exchange flow on the rise velocity of a gas slug is considered, and that of the gas slug on the geometry of an exchange flow. Analogue experiments are presented of gas slugs ascending through exchange flow with (3 > 1, scaled to basaltic volcanoes using the Reynolds, Eotvos, Froude and Strouhal numbers. Gas slugs rise through, and are constrained by the less viscous ascending fluid. Their rise velocities are shown to be a linear combination of the liquid velocity ahead of the gas slug and the rise velocity of the slug due to buoyancy. Its buoyant rise velocity is a function of the liquid viscosity, density and surface tension, and the lateral dimension of the less viscous fluid which it is constrained by. Given the calculated magma properties for ascending and descending magma at Stromboli gas slugs ascending through an exchange flow have velocities ranging from 1 - 3 m s-l. Further, experiments conducted in inclined pipes suggest that velocities may be increased by up to 56% in a conduit inclined from the vertical.
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Collins, S. J. "Degassing of volatiles and semi-volatile trace elements at basaltic volcanoes". Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597860.
Testo completoAbstract (sommario):
At Mt. Etna, Italy, vigorous gas-rich eruptions in 2001, 2002 and 2003 were followed by gas-poor eruptions in 2004, 2006 and 2007. Contrary to expectation, melt inclusion compositions indicate that magmas erupted between 2004 to 2007 did not follow similar degassing paths as recorded in 2001 and 2002 and that are expected from the solubility laws of CO2 and H2O. Instead melts stored in the plumbing system since 2002 reequilibrated with CO2-rich gases from depth. Sustained gas percolation caused loss of water and enhancement of CO2 in the evolving melt. At Piton de la Fournaise melt inclusions trapped in olivines record degassing of various batches of magma and the fractionation of olivines at various depths within the plumbing system. The host melt which carries these olivines to the surface represents an infiltration of new magma which erupts rapidly incorporating olivines along the way. The host melt also records processes of diffusive fractionation during groundmass crystallisation. Semi-volatile trace metals and Li have been found to behave in a volatile fashion at both Mt. Etna and Piton de la Fournaise. At Mt. Etna, CO2 gas fluxing may have been important for causing the transfer of Cu from magmas at depth, to magmas stored in the shallow plumbing system. At Piton de la Fournaise trace metals are not simply behaving as incompatible elements but rather show the influence S and H2O loss during degassing. However, when investigating trace metal concentrations in volcanic products this thesis shows that the affect of sulphide immiscibility should not be neglected. Loss of chalcophile trace metals to sulphide melts prevents partitioning of the element into a gas phase. Destabilisation of these melts on the other hand, may release enriched concentrations of trace metals to a gas phase.
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Edwards, James Anthony. "Modelling stresses around the volcanoes of Kilauea, Hawaii and NW Scotland". Thesis, University of Leeds, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431895.
Testo completo
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Brian, Antony William. "A study of large volcanoes and their geological settings on Venus". Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268441.
Testo completo
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Tuyisingize, Deogratias. "Terrestrial small mammal community composition in the Volcanoes National Park, Rwanda". Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/4763.
Testo completo
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Bone, B. D. "The geological evolution of the S.W. Naivasha volcanic complex". Thesis, Lancaster University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379196.
Testo completo
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Wooster, Martin John. "Spaceborne monitoring of high temperature volcanic thermal features : studies using the ERS Along Track Scanning Radiometer". Thesis, Open University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264468.
Testo completo
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Woods, Jennifer. "Dyke-induced earthquakes during the 2014-15 Bárðarbunga-Holuhraun rifting event, Iceland". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/289448.
Testo completoAbstract (sommario):
Understanding dykes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions. The 2014-15 Bárðarbunga-Holuhraun rifting event comprised the best-monitored dyke intrusion to date and the largest eruption in Iceland in 230 years. Over a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano, Iceland, along a 48 km path before erupting in the Holuhraun lava field on 29 August 2014. A huge variety of seismicity was produced, including over 30,000 volcano-tectonic earthquakes (VTs) associated with the dyke propagation at ∼ 6 km depth below sea level, and long-period seismicity - both long-period earthquakes (LPs) and tremor - associated with the eruption processes. The Cambridge University seismic network in central Iceland recorded the dyke seismicity in unprecedented detail, allowing high resolution analyses to be carried out. This dissertation comprises two parts: study of 1) the volcano-tectonic dyke-induced seismicity and 2) the long-period seismicity associated with eruption processes. Volcano-tectonic earthquakes induced by the lateral dyke intrusion were relocated, using cross-correlated, sub-sample relative travel times. The ∼ 100 m spatial resolution achieved reveals the complexity of the dyke propagation pathway and dynamics (jerky, segmented), and allows us to address the precise relationship between the dyke and seismicity. The spatio-temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dyke, and following this - after dyke opening - indicate a relationship with magma pressure changes (i.e. dyke inflation/deflation), followed by a general 'post-opening' decay. Seismicity occurs only at the base of the dyke, where dyke-imposed stresses - combined with the background tectonic stress (from regional extension over > 200 years since last rifting) - are sufficient to induce failure of pre-existing weaknesses in the crust, while the greatest opening is at shallower depths. Emplacement oblique to the spreading ridge resulted in left-lateral shear motion along the distal dyke section (studied here), and a prevalence of left-lateral shear failure. Fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters, indicating that they are controlled by the underlying host rock fabric. Long-period earthquakes and tremor were systematically detected and located during the dyke propagation phase and the first week of the eruption. Clusters of highly similar, repetitive LPs were identified, with a peak frequency of ∼ 1 Hz and clear P and S phases followed by a long-duration coda. The source mechanisms were remarkably consistent between clusters and also fundamentally different to those of the VTs. The clusters were accurately located near each of three ice cauldrons (depressions formed by basal melting) that were observed on the surface of Dyngjujökull glacier above the path of the dyke. Most events were in the vicinity of the northernmost cauldron, at shallower depth than the VTs associated with lateral dyke propagation. At the two northerly cauldrons, periods of shallow seismic tremor following the clusters of LPs were also observed. Given that the LPs occurred at ∼ 4 km depth and in swarms during times of dyke-stalling, it is inferred that they result from excitation of magmatic fluid-filled cavities and indicate magma ascent. The tremor may then represent the climax of the vertical melt movement, arising from either rapid, repeated excitation of the same LP cavities, or sub-glacial eruption processes. This long-period seismicity therefore highlights magma pathways between the depth of the dyke-VT earthquakes and the surface. Notably, no tremor is detected associated with each cauldron, despite melt reaching the base of the overlying ice cap, a concern for hazard forecasting.
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McCormick, Brendan Thomas. "Measuring volcanic sulphur dioxide degassing with the satellite-based Ozone Monitoring Instrument". Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648608.
Testo completo
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Contreras, Vargas María Angélica. "The control of magmatic system properties on volcano dimensions and building: The cases of Lascar, Lonquimay and Llaima volcanoes, Andes of Chile". Tesis, Universidad de Chile, 2017. http://repositorio.uchile.cl/handle/2250/149095.
Testo completoAbstract (sommario):
Magíster en Ciencias, Mención GeologíaLos estratovolcanes son la manifestación en superficie de complejos sistemas magmáticos profundos. En el presente trabajo, se ha desarrollado un modelo cuyo objetivo es contribuir a la comprensión de la influencia de las propiedades del sistema magmático de un estratovolcán, en el perfil topográfico y dimensiones del mismo. Se asume un volcán construido por la acumulación de flujos de lava emitidos desde un centro de emisión único, excluyendo otros procesos que pueden afectar el crecimiento tales como erosión, avalanchas, volcanismo adventicio, acumulación de piroclastos, entre otros. Se considera que cada erupción es gatillada por la inyección de nuevo magma en el reservorio, y que la resultante sobrepresión asociada provoca la removilización de una parte del magma almacenado que es posteriormente extruido. El modelo se probó en 3 estratovolcanes de los Andes de Chile, con diferencias morfológicas y composicionales: el volcán Lascar ubicado en la Zona Volcánica Central, y los volcanes Lonquimay y Llaima localizados en la Zona Volcánica Sur. Los resultados obtenidos tras aplicar el modelo fueron validados con otros métodos independientes: termobarometría en muestras seleccionadas de estos volcanes y estudios geofísicos previos. Los resultados obtenidos revelan una fuerte influencia de las propiedades del sistema magmático en la morfología de los volcanes en superficie. Volcanes que superan los 2000 m de altura desde su base y poseen un radio basal de más de 10 km, estarían asociados a cámaras profundas, ubicadas a más de 10 km bajo la superficie. En volcanes de altura menor a 1500 m y radio basal menor a 10 km, el reservorio alimentador de las erupciones se ubicaría a menos de 6 km de profundidad. Si además se considera la densidad de la corteza y del magma, esto es más complejo pues a mayor flotabilidad se espera un estratovolcán más alto. Por otra parte, mientras mayor es el tamaño del reservorio, los flujos de lava emitidos también lo serán y, en consecuencia, se espera un radio basal mayor y un volcán de mayor volumen. Nuestro análisis sugiere que los volcanes Lonquimay y Llaima están cerca de alcanzar su altura máxima, por lo tanto, erupciones efusivas de volumen considerable ocurrirían probablemente en sus flancos, mientras que erupciones más bien moderadas son esperables que ocurran desde su cima. Al contrario, el volcán Lascar no habría alcanzado su altura máxima, en consecuencia, flujos de lava de volumen considerable podrían ser emitidos desde la cima.
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Giuffrida, Marisa. "Magma storage, ascent and degassing histories traced by textures and chemical zoning in crystals: application to the C02-Rich basaltic system of Mt. Etna Volcano". Doctoral thesis, Università di Catania, 2018. http://hdl.handle.net/10761/3632.
Testo completoAbstract (sommario):
An extensive compositional dataset of plagioclase and olivine crystals from lavas emitted between the 2011 and 2013 at Mt. Etna has been used to constrain modes and timescales of magma storage and transfer to the surface. Plagioclase crystals display either near-equilibrium or disequilibrium textures at the core and rim that indicate complex histories of magma crystallization under variable chemical and physical conditions. Crystals with different textures have been characterized for major (An), minor (Fe and Mg) and trace elements (Sr/Ba). The Sr /Ba ratio in oscillatory-zoned plagioclase revealed the presence into the plumbing system of low-Sr magma volumes that preserve a geochemical signature similar to that of magmas feeding the historic, pre-1971 activity. Fe and Mg zoning vs anorthite in correspondence of plagioclase sieve textures also suggest that processes of gas-flushing have had a dominant role in triggering the paroxysmal eruption, determining a sudden intensification of the eruption intensity up to the fountaining phase. In order to interpret the range of crystal textures and compositions that may form in CO2-rich systems, a series of experiments was conducted to reproduce processes of CO2-flushing at distinct sections of the plumbing system. Starting from an initial material containing a pure-H2O fluid, experiments were performed at temperature of 1080°C and at two distinct pressures of 100 MPa and 300 MPa, using volatile mixtures at variable H2O+CO2 concentrations. Results show that CO2-flushing at high pressure greatly promote plagioclase destabilization during their early grow history, and is therefore one of the main mechanism responsible for the spectrum of disequilibrium textures at the plagioclase cores. The transfer and injection of prevalent CO2-rich gases at shallow (~100MPa) depth mostly reduce the clinopyroxene stability, causing severe destabilization of their rims. Through Sr-diffusion modelling in plagioclase the maximum time of magma storage during the considered eruptive period has been evaluated. Timescales of crystal residence in the plumbing system are short (five years to three decades), suggesting limited magma storage and faster transfer dynamics to the surface. The investigation of Li diffusion in plagioclase allow a direct quantification of magma ascent and vesiculation upon eruption. Li diffusion calculations yield timescales of sin-eruptive magma ascent between 20 and 30 sec, corresponding to rates of 50-75 m/s. Chemical zoning of olivine crystals highlights processes of multi-step magma transfer and residence at different levels of the plumbing system. The migration of magmas to the surface occurred primarily stepwise through multiple episode of injection and mixing between five compositionally-distinct magmatic environments (Mi), whose P-T- O2 characteristics and concentrations in dissolved volatiles were constrain by thermodynamic modeling. From a deepest reservoir, located at depth of ~600 MPa, the most primitive magma M1 (Fo84) moved along dominant pathways, intercepting the M2 (Fo80-82) at ~390 MPa and/or M3 (Fo78; 250 MPa), M4 (Fo75; ~140 MPa) and finally the shallow M5 (Fo70-73; ~40 MPa) storage zone. For some eruptive episodes, olivine zonings highlight a preferential route of transfer, connecting the M1 and M5 storage zones that facilitated the migration of primitive magma at shallow depth. Fe-Mg diffusion modelling on olivine normal and reverse zoning defines the timescales of magma transfer and storage across these magmatic environments, which vary from ~1 to 18 months, whereas intrusion and mixing by more basic magma into the shallowest reservoir occurred always within 5 months before eruption. Relevance of this study mainly relies on the quantification of volcanic processes at depth that may have considerable consequences in development of unusual, high-energy eruptions at basaltic volcanoes, generally acknowledged for their weak to mild explosive activity.