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1
Waythomas, C. F., P. Watts, and J. S. Walder. "Numerical simulation of tsunami generation by cold volcanic mass flows at Augustine Volcano, Alaska." Natural Hazards and Earth System Sciences 6, no. 5 (July 26, 2006): 671–85. http://dx.doi.org/10.5194/nhess-6-671-2006.
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Abstract. Many of the world's active volcanoes are situated on or near coastlines. During eruptions, diverse geophysical mass flows, including pyroclastic flows, debris avalanches, and lahars, can deliver large volumes of unconsolidated debris to the ocean in a short period of time and thereby generate tsunamis. Deposits of both hot and cold volcanic mass flows produced by eruptions of Aleutian arc volcanoes are exposed at many locations along the coastlines of the Bering Sea, North Pacific Ocean, and Cook Inlet, indicating that the flows entered the sea and in some cases may have initiated tsunamis. We evaluate the process of tsunami generation by cold granular subaerial volcanic mass flows using examples from Augustine Volcano in southern Cook Inlet. Augustine Volcano is the most historically active volcano in the Cook Inlet region, and future eruptions, should they lead to debris-avalanche formation and tsunami generation, could be hazardous to some coastal areas. Geological investigations at Augustine Volcano suggest that as many as 12–14 debris avalanches have reached the sea in the last 2000 years, and a debris avalanche emplaced during an A.D. 1883 eruption may have initiated a tsunami that was observed about 80 km east of the volcano at the village of English Bay (Nanwalek) on the coast of the southern Kenai Peninsula. Numerical simulation of mass-flow motion, tsunami generation, propagation, and inundation for Augustine Volcano indicate only modest wave generation by volcanic mass flows and localized wave effects. However, for east-directed mass flows entering Cook Inlet, tsunamis are capable of reaching the more populated coastlines of the southwestern Kenai Peninsula, where maximum water amplitudes of several meters are possible.
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Oppenheimer, Clive. "Climatic, environmental and human consequences of the largest known historic eruption: Tambora volcano (Indonesia) 1815." Progress in Physical Geography: Earth and Environment 27, no. 2 (June 2003): 230–59. http://dx.doi.org/10.1191/0309133303pp379ra.
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The 1815 eruption of Tambora volcano (Sumbawa island, Indonesia) expelled around 140 gt of magma (equivalent to ≈50 km3 of dense rock), making it the largest known historic eruption. More than 95% by mass of the ejecta was erupted as pyroclastic flows, but 40% by mass of the material in these flows ended up as ash fallout from the ‘phoenix’ clouds that lofted above the flows during their emplacement. Although they made only a minor contribution to the total magnitude of the eruption, the short-lived plinian explosions that preceded the climactic eruption and caldera collapse were powerful, propelling plumes up to 43 km altitude. Over 71 000 people died during, or in the aftermath of, the eruption, on Sumbawa and the neigh-bouring island of Lombok. The eruption injected ≈60 mt of sulfur into the stratosphere, six times more than was released by the 1991 Pinatubo eruption. This formed a global sulfate aerosol veil in the stratosphere, which resulted in pronounced climate perturbations. Anomalously cold weather hit the northeastern USA, maritime provinces of Canada, and Europe the following year. 1816 came to be known as the ‘Year without a summer’ in these regions. Crop failures were widespread and the eruption has been implicated in accelerated emigration from New England, and widespread outbreaks of epidemic typhus. These events provide important insights into the volcanic forcing of climate, and the global risk of future eruptions on this scale.
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Hamling, I. J., and G. Kilgour. "Goldilocks conditions required for earthquakes to trigger basaltic eruptions: Evidence from the 2015 Ambrym eruption." Science Advances 6, no. 14 (April 2020): eaaz5261. http://dx.doi.org/10.1126/sciadv.aaz5261.
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Observations indicate a strong correlation between the occurrence of volcanic eruptions and earthquakes. While increased volcanic activity has been observed following both local and distal earthquakes, some of the largest recorded earthquakes aren’t known to have triggered an eruption. Here we investigate whether an eruption and associated dike intrusion at Ambrym volcano was triggered by an Mw 6.4 earthquake which occurred 30 hours earlier. Modeling suggests that stress changes induced by the earthquake were too small to account for the overpressure in the dike without additional bubble growth to pressurize the magma chamber. We find that the magma must be both H2O-saturated and at lower temperatures than those expected for newly intruded basalts. Too hot and the stress drop required to grow the bubbles is too large, too cold and the magma can no longer flow. These observations suggest that partially cooled and crystallized basaltic magmas are more susceptible to triggering from earthquakes.
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Lister, John R., and Paul J. Dellar. "Solidification of pressure-driven flow in a finite rigid channel with application to volcanic eruptions." Journal of Fluid Mechanics 323 (September 25, 1996): 267–83. http://dx.doi.org/10.1017/s0022112096000912.
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Competition between conductive cooling and advective heating occurs whenever hot fluid invades a cold environment. Here the solidification of hot viscous flow driven by a fixed pressure drop through an initially planar or cylindrical channel embedded in a cold rigid solid is analysed. At early times, or far from the channel entrance, the flow starts to solidify and block the channel, thus reducing the flow rate. Close to the channel entrance, and at later times, the supply of new hot fluid starts to melt back the initial chill. Eventually, either solidification or meltback becomes dominant throughout the channel, and flow either ceases or continues until the source is exhausted. The evolution of the dimensionless system, which is characterized by the initial Péclet number Pe, the Stefan number S and the dimensionless solidification temperature Θ, is calculated numerically and by a variety of asymptotic schemes. The results show the importance of variations along the channel and caution against models based on a single ‘representative’ width. The critical Péclet number Pec, which marks the boundary between eventual solidification and eventual meltback, is determined for a wide range of parameters and found to be much larger for cylindrical channels than for planar channels, owing to the slower rate of decay of the heat flux into the solid in a cylindrical geometry. For a planar channel Pec is given by the simple algebraic result Pec ∼ 0.46[Θ2/(1 - Θ)(S + 2/π)]3 when (1 - Θ)−1 [Gt ] S [Gt ] 1, but in general it requires numerical solution. Similar analyses, in which there is a spatially varying and time-dependent interaction between the rates of solidification and flow, have a range of applications to geological and industrial processes.
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Becerra-Ramírez, Rafael, Rafael U. Gosálvez, Estela Escobar, Elena González, Mario Serrano-Patón, and Darío Guevara. "Characterization and Geotourist Resources of the Campo de Calatrava Volcanic Region (Ciudad Real, Castilla-La Mancha, Spain) to Develop a UNESCO Global Geopark Project." Geosciences 10, no. 11 (November 6, 2020): 441. http://dx.doi.org/10.3390/geosciences10110441.
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The Campo de Calatrava Volcanic Region is located in Central Spain (Ciudad Real province, Castilla-La Mancha) where some eruptions of different intensity and spatial location took place throughout a period of more than 8 million years. As a result, more than 360 volcanic edifices spread over 5000 km2. Eruptions of this volcanic system were derived from alkaline magmas with events of low explosivity (Hawaiian and Strombolian). These events are characterized by three different manifestations: the emission of pyroclasts (cinder and spatter cones) and lava flows; some hydromagmatic events, which lead to the formation of wide craters (maars) and pyroclastic flows; and remnant volcanic activity related to gas emission (CO2), hot springs (hervideros) and carbonic water fountains (fuentes agrias). The methods used for this study are based on analytical studies of geography, geomorphology and geoheritage to identify volcanoes and their resources and attractions linked to the historical-cultural heritage. These volcanoes are a potential economic resource and attraction for the promotion of volcano tourism (geotourism), and they are the basis for achieving a UNESCO Global Geopark Project, as a sustainable territorial and economic management model, to be part of the international networks of conservation and protection of nature and, especially, that of volcanoes.
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Koulakov, Ivan, Ekaterina Boychenko, and Sergey Z. Smirnov. "Magma Chambers and Meteoric Fluid Flows Beneath the Atka Volcanic Complex (Aleutian Islands) Inferred from Local Earthquake Tomography." Geosciences 10, no. 6 (June 2, 2020): 214. http://dx.doi.org/10.3390/geosciences10060214.
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Atka is a subduction-related volcanic island located in the central part of Aleutian Arc. The northeastern part of this island forms the Atka Volcanic Complex (AVC), which is built as a relict shield volcano of a circular shape overlain by several active and extinct volcanic vents of different ages. During the past few decades, two active volcanoes within AVC—Korovin and Kliuchef—demonstrated mostly phreatic eruptions and intensive fumarolic activity. We have created the first tomographic model of the crust beneath AVC with the use of data of eight permanent stations of the Alaskan Volcanological Observatory operated in the time period from 2004 to 2017 that included arrival times of the P and S waves from local seismicity. Based on a series of checkerboard tests, we have demonstrated fair vertical and horizontal resolution of the model down to ~6 km depth. Beneath the Korovin and Kliuchef volcanoes, we have revealed two isolated anomalies of high Vp/Vs with values exceeding 2, which represent separate magma chambers that are responsible for magmatic eruptions of these two volcanoes. In shallow layers down to 2–3 km deep, we observe an alternation of zones with low and high values of the Vp/Vs ratio, which are likely associated with the circulation of meteoric fluids in the uppermost crust. Moderately high Vp/Vs anomalies indicate zones of meteoric water penetration down to the ground. On the other hand, the very low values of Vp/Vs reaching 1.5 depict the areas where meteoric water reached the hot magma reservoir and transformed into steam. On the surface, these zones coincide with the distributions of fumaroles. The outflow of these steam currents from active vents of Korovin and Kliuchef led to episodic phreatic eruptions, sometimes synchronous.
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Lister, John R. "The solidification of buoyancy-driven flow in a flexible-walled channel. Part 1. Constant-volume release." Journal of Fluid Mechanics 272 (August 10, 1994): 21–44. http://dx.doi.org/10.1017/s0022112094004362.
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The solidification of hot fluid flowing in a thin buoyancy-driven layer between cold solid boundaries is analysed in a series of two papers. As an approximation to flow in a crack in a weakly elastic solid or to free-surface flow beneath a thin solidified crust, the boundaries are considered to be flexible and to exert negligible resistance to lateral deformation. The resultant equations of continuity and motion reduce to a kinematic-wave equation with a loss term corresponding to the accumulation of solidified material at the boundaries. The Stefan problem for the solidification is coupled back to the flow through the advection of heat by the fluid, which competes with lateral heat loss by conduction to the solid. Heat and mass conservation are used to derive boundary conditions at the propagating nose of the flow. In this paper the two-dimensional flow produced by a line release of a given volume of fluid is investigated. It is shown that at short times the flow solidifies completely only near the point of release where the flow is thinnest, at later times complete solidification also occurs near the nose of the flow where the cooling rates are greatest and, eventually, the flow is completely solidified along its depth. Some transient melting of the boundaries can also occur if the fluid is initially above its solidification temperature. The dimensionless equations are parameterized only in terms of a Stefan number S and a dimensionless solidification temperature Θ. Asymptotic solutions for the flow at short times and near the source are derived by perturbation series and similarity arguments. The general evolution of the flow is calculated numerically, and the scaled time to final solidification, the length and the thickness of the solidified product are determined as functions of S and Θ. The theoretical solutions provide simple models of the release of a pulse of magma into a fissure in the Earth's lithosphere or of lava flow on the flanks of a volcano after a brief eruption. Other geological events are better modelled as flows fed by a continual supply of hot fluid. The solidification of such flows will be investigated in Part 2.
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Wylie, Jonathan J., and John R. Lister. "The effects of temperature-dependent viscosity on flow in a cooled channel with application to basaltic fissure eruptions." Journal of Fluid Mechanics 305 (December 25, 1995): 239–61. http://dx.doi.org/10.1017/s0022112095004617.
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A theoretical description is given of pressure-driven viscous flow of an initially hot fluid through a planar channel with cold walls. The viscosity of the fluid is assumed to be a function only of its temperature. If the viscosity variations caused by the cooling of the fluid are sufficiently large then the relationship between the pressure drop and the flow rate is non-monotonic and there can be more than one steady flow for a given pressure drop. The linear stability of steady flows to two-dimensional and three-dimensional disturbances is calculated. The region of instability to two-dimensional disturbances corresponds exactly to those flows in which an increase in flow rate leads to a decrease in pressure drop. At higher viscosity contrasts some flows are most unstable to three-dimensional (fingering) instabilities analogous, but not identical, to Saffman-Taylor fingering. A cross-channel-averaged model is derived and used to investigate the finite-amplitude evolution.
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Stewart, M. L., J. K. Russell, and C. J. Hickson. "Discrimination of hot versus cold avalanche deposits: Implications for hazard assessment at Mount Meager, B.C." Natural Hazards and Earth System Sciences 3, no. 6 (December 31, 2003): 713–24. http://dx.doi.org/10.5194/nhess-3-713-2003.
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Abstract. The surficial deposits surrounding the Mount Meager volcanic complex include numerous avalanche deposits. These deposits share many attributes: (a) they are nearly monolithologic and comprise mainly intermediate volcanic rock clasts, (b) they lack internal structure, and (c) they are very poorly sorted. Despite these similarities, the avalanche deposits represent two distinct processes. Mass wasting of the Mount Meager volcanic edifice has produced cold rock avalanche deposits, whereas gravitational collapse of active lava domes and flows has produced hot block and ash avalanche deposits. The ability to discriminate between these "hot" and "cold" avalanche deposits is a critical component in the assessment of hazards in volcanic terranes. Hot block and ash avalanche deposits can be distinguished by the presence of radially-oriented joints, breadcrust textures, and incipient welding, which are features indicative of high emplacement temperatures. Conversely, rock avalanche deposits resulting from mass wasting events may be distinguished by the presence of clasts that preserve pre-depositional weathering and jointing surfaces. Volcanic avalanches are mechanically similar to rock avalanches but pose a greater hazard due to high temperatures, increased fluidization from degassing and the potential to decouple highly mobile elutriated ash clouds. The increasing use of hazardous regions such as the Lillooet River valley requires more reliable risk assessment in order to minimize losses from future hazardous events.
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Solomina, O., I. Pavlova, A. Curtis, G. Jacoby, V. Ponomareva, and M. Pevzner. "Constraining recent Shiveluch volcano eruptions (Kamchatka, Russia) by means of dendrochronology." Natural Hazards and Earth System Sciences 8, no. 5 (October 15, 2008): 1083–97. http://dx.doi.org/10.5194/nhess-8-1083-2008.
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Abstract. Shiveluch (N 56°38´, E 161°19´; elevation: active dome ~2500 m, summit of Old Shiveluch 3283 m) is one of the most active volcanoes in Kamchatka. The eruptions of Shiveluch commonly result in major environmental damage caused by debris avalanches, hot pyroclastic flows, tephra falls and lahars. Constraining these events in time and space is important for the understanding and prediction of these natural hazards. The last major eruption of Shiveluch occurred in 2005; earlier ones, dated by instrumental, historical, 14C and tephrochronological methods, occurred in the last millennium around AD 1030, 1430, 1650, 1739, 1790–1810, 1854, 1879–1883, 1897–1898, 1905, 1927–1929, 1944–1950, and 1964. A lava dome has been growing in the 1964 crater since 1980, occasionally producing tephra falls and pyroclastic flows. Several Shiveluch eruptions (~AD 1050, 1650, 1854, 1964) may have been climatically effective and are probably recorded in the Greenland ice cores. Previously, most dates for eruptions before AD 1854 were obtained by tephrochronology and constrained by radiocarbon dating with an accuracy of several decades or centuries. In this paper we report tree-ring dates for a recent pyroclastic flow in Baidarnaia valley. Though the wood buried in these deposits is carbonized, fragile and poorly preserved, we were able to measure ring-width using standard tree-ring equipment or photographs and to cross-date these samples against the regional Kamchatka larch ring-width chronology. The dates of the outer rings indicate the date of the eruptions. In the Baidarnaia valley the eruption occurred shortly after AD 1756, but not later than AD 1758. This date coincides with the decrease of ring-width in trees growing near Shiveluch volcano in 1758–1763 in comparison with the control "non-volcanic" chronology. The pyroclastic flow in Kamenskaia valley, although similar in appearance to the one in Baidarnaia valley, definitively yielded a different age. Due to the age limit of the reference chronology (AD 1632–2005) and its short overlap with the sample chronology in Kamenskaia valley the dates of these deposits are very preliminary. The deposits probably date back to approximately AD 1649 or a few years later. This date is in close agreement with the previously obtained radiocarbon date of these sediments to AD 1641(1652)1663. Our data agree well with the tephrochronological findings, and further constrain the chronology of volcanic events in this remote area.
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Picard, Christian, and Michel Piboule. "Pétrologie des roches volcaniques du sillon de roches vertes archéennes de Matagami – Chibougamau à l'ouest de Chapais (Abitibi est, Québec).1. Le groupe basal de Roy." Canadian Journal of Earth Sciences 23, no. 4 (April 1, 1986): 561–78. http://dx.doi.org/10.1139/e86-056.
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In the northeastern part of the Abitibi orogenic belt, the Archean Matagami–Chibougamou greenstone belt (2700 Ma) includes a basal volcanic sequence named the Roy Group, unconformably overlain by a volcano-sedimentary series called the Opemisca Group.The Roy Group, to the west of the town of Chapais, consists of a thick, stratified, and polycyclic volcanic series (thickness = 11 000 m) resembling the large, western Abitibi submarine stratovolcanoes constructed by three mafic to felsic magmatic cycles. The first cycle (Chrissie Formation) shows lateral spreading and is composed only of a meta-andesite and felsic pyroclastite sequence of calc-alkaline affinity. The other two cycles (Obatogamau and Waconichi formations; then Gilman, Blondeau, and Scorpio formations) are characterized by a sequence of repeated MORB type basaltic lava flows of tholeiitic affinity and by intermediate to acid lava and pyroclastic sequences calc-alkaline affinity.The stratigraphic and petrographic data suggest emplacement of mafic lavas on an abyssal plain (Obatogamau Formation) or at a later time on the flanks of a large submarine volcanic shield (Gilman and Blondeau formations). The lava and felsic pyroclastite flows were formed by very explosive eruptions from central spreading type volcanoes above a pre-existing continental crust. In particular, the Scorpio volcanic rocks were emplaced on volcanic islands later dismantled by erosion.The contents and distribution of trace elements and rare earths show that basaltic lavas resulted from an equilibrium partial melting (F = 15–35%) of spinel lherzolite type mantle sources depleted to weakly enriched in Th, Ta, Nb, and light rare-earth elements (LREE), and from fractional crystallization at low pressure of feldspar, clinopyroxene, and olivine. The lavas and the felsic pyroclastites of the Waconichi and Scorpio formations appear to result from partial melting of a mantle source of lherzolite type enriched in LREE and involving some garnet. At a late stage, the melts were probably contaminated by some continental crust materials and then differentiated by fractional crystallization of plagioclase, amphibole, biotite, and magnetite. The lavas in the Chrissie Formation and the middle member of the Gilman Formation seem to result from partial melting of a mantle source enriched in LREE with a composition between the two described above. They were subsequently modified by fractional crystallization of the plagioclase, clinopyroxene, olivine, and titanomagnetite.In general, the mafic to felsic magmatic cycles observed are characterized by a thick sequence of repeated tholeiitic basalt flows similar to those of modern mid-oceanic ridges and by a lava and felsic pyroclastite sequence of calc-alkaline affinity comparable to those occurring in orogenic belts. The transition from one lava sequence to another is marked by a significant chemical discontinuity, and the mantle sources exhibit an increasing enrichment in LREE during a given magmatic cycle. A model is proposed to satisfactorily explain all the stratigraphic, petrographic, and geochemical data implying a hot spot type mechanism, which could be responsible for the cyclic, rising diapirs inside the stratified Archean mantle and for initiating the repeated mantle source meltings, depleted and enriched in LREE, respectively. [Journal Translation]
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Lerner, Geoffrey A., Shane J. Cronin, Gillian M. Turner, and Elisa J. Piispa. "Recognizing long-runout pyroclastic flow deposits using paleomagnetism of ash." GSA Bulletin 131, no. 11-12 (April 9, 2019): 1783–93. http://dx.doi.org/10.1130/b35029.1.
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Abstract Quantifying the spread of >600 °C pyroclastic flows (more broadly termed pyroclastic density currents—PDCs) is important because they regularly cause major volcanic catastrophes. Far from volcanic flanks, non-welded PDC deposits can be difficult to distinguish from cold-emplaced volcano-sedimentary units. A key indicator of high temperature is the coherence of magnetic remanence among different lithic clasts in a deposit. In long-runout PDCs, distal deposits are dominated by ash particles (<2 mm diameter), often lacking clasts large enough for conventional paleomagnetic sampling. Here we demonstrate a method of consolidating and sampling oriented blocks of friable ash material with a strengthening compound. This method was used to show that a >25 km runout mass-flow deposit from the 2518-m-high Mt. Taranaki (New Zealand) was emplaced as a hot PDC, contrary to an earlier cold lahar interpretation. We corroborate the results from ash with data from clast samples at some sites and show that the matrix was emplaced at temperatures of at least 250 °C, while clasts were deposited at up to 410 °C. Our case-study raises concerns for hazard-identification at stratovolcanoes worldwide. In the Mt. Taranaki case we demonstrate that PDCs traveled >9 km farther than previously estimated—also well beyond the “normal” PDC hazard zones at stratovolcanoes (10 or 15 km from source). Thus, attention should be paid to deposits in the 15–25 km range in other volcanic settings, where large populations are potentially unaware of PDC risk.
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Lister, John R. "The solidification of buoyancy-driven flow in a flexible-walled channel. Part 2. Continual release." Journal of Fluid Mechanics 272 (August 10, 1994): 45–66. http://dx.doi.org/10.1017/s0022112094004374.
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The model developed in Part 1 (Lister 1994) for the solidification of hot fluid flowing in a thin buoyancy-driven layer between cold solid but freely deformable boundaries is extended to study the case of continual release of fluid. In this model lubrication theory was applied to reduce the equations of mass and heat conservation to a kinematic-wave equation and an advection-diffusion equation, which were coupled by the rate of solidification. The equations allow the source flux to be specified, and the cases of constant input and of flux proportional to a power of time are considered here. The structure of the flow differs significantly from the case of constant-volume release considered in Part 1. The advective resupply of heat prevents the flow from solidifying completely at the source and, if the initial fluid temperature is greater than the melting temperature of the solid, will in fact lead to rapid melting near the source. A perturbation expansion is used to describe the development of thermal boundary layers at the flow margins and the initial self-similar extension of the zone of melting. As the flow propagates beyond its thermal entry length, the fluid temperature falls to the liquidus value and melting gives way to solidification. At large times nearly all of the fluid supplied solidifies against the margins of the flow but, provided the source flux decreases less rapidly than t−½, sufficient reaches the nose of the flow that the flow continues to increase in length indefinitely. Analytic solutions are given for this long-time regime showing, for example, that the length increases asymptotically like t1/2 for constant-flux input. The theoretical solutions, which are calculated by a combination of analytic and numerical methods, may be used to describe the propagation of a dyke fed by a large body of magma through the Earth's lithosphere or the flow of lava down the flanks of a volcano during an extensive period of eruption.
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Kennedy, Kirsten, and Nicholas Eyles. "Subaqueous debrites of the Grand ConglomÉrat Formation, Democratic Republic of Congo: A model for anomalously thick Neoproterozoic: “Glacial” diamictites." Journal of Sedimentary Research 89, no. 10 (October 21, 2019): 935–55. http://dx.doi.org/10.2110/jsr.2019.51.
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ABSTRACT Very thick (> 1 km) successions of matrix-supported conglomerates (diamictites) are a very distinctive component of many Neoproterozoic basins. Classically interpreted as glacially deposited sedimentary rocks, their thickness has been seen as requiring exceptional depositional conditions such as world-wide “panglacial” climates. The Neoproterozoic Grand Conglomérat Formation (GC) of Katanga Province, southeastern Democratic Republic of Congo, is a 1.8-km-thick diamictite succession hosting one of the world's largest stratiform copper deposits. Examination of more than 300 km of recently acquired large diameter (up to 4 inches, 10.2 cm) core identifies the diamictites of the GC as debrites that accumulated as part of a deep-water “mass-transport complex” in a tectonically active and volcanically influenced anoxic rift basin. Detailed sedimentological descriptions of debrite facies and their lateral and vertical variability permits new insights into processes of debris-flow formation and transport, and their wider paleoenvironmental and paleotectonic significance. A genetic model is herein presented that highlights the importance of slumping and subaqueous downslope mixing of basin-margin fan-delta gravels, fault breccias, volcanic debris from contemporaneous basaltic fissure eruptions with basinal muds, and the downslope ponding of flows in narrow fault-bounded depocenters. Preservation of such an exceptionally thick subaqueously deposited debrite-dominated mass transport complex lacking any evidence of shallow-water deposition, requires rapid subsidence. Any direct sedimentary evidence of a glacial influence on sedimentation in the wider basin hinterland (if present) has been destroyed and homogenized by mass flow. Indirect evidence of a cold-climate setting is possibly expressed as lonestones in laminated turbidite facies dropped by either glacial or seasonal ice, and by exceptionally rare scratched clasts that may have been striated subglacially. Descriptions and interpretations presented here provide clues to the origin of other unusually thick debrite and turbidite successions elsewhere in other Neoproterozoic basins; their primary paleoenvironmental significance is that they appear to record ponding and focusing of mass flows in narrow, rapidly subsiding fault-bounded depocenters, rather than any unique glacial paleoclimate.
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"Ancient extinct life forms fossilized through volcanism in sedimented rivers and other plains of Mars." International Journal of Natural Science and Reviews, 2021, 18. http://dx.doi.org/10.28933/ijnsr-2021-07-0905.
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The use of rules laid in earlier articles of the author allows to isolate the remains of life forms on Mars. All of these life forms have perished in volcanic eruptions. Pyroclastic flows, mudslides and the lava fill-up of underwater caves are shown to have killed by surprise the animals. The violence of the event allows conservation of the remains, as the covering by tuf, lava, hot mud, allows the casting of rock molds. An early observation of a femur in 2014 was discarded as result of erosion. This finding comes together with a skull cast in stone. It is indeed a skull and a femur – this can be validated ex-post by crossing with the findings of the author in an earlier article and these new ones.
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Dahl-Jensen, Trine, W. Steven Holbrook, John R. Hopper, Peter B. Kelemen, Hans Christian Larsen, Robert Detrick, Stefan Bernstein, and Graham Kent. "Seismic investigation of the East Greenland volcanic rifted margin." GEUS Bulletin, June 1, 1997, 50–54. http://dx.doi.org/10.34194/ggub.v176.5061.
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NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example:
Dahl-Jensen, T., Holbrook, W. S., Hopper, J. R., Kelemen, P. B., Larsen, H. C., Detrick, R., Bernstein, S., & Kent, G. (1997). Seismic investigation of the East Greenland volcanic rifted margin. Geology of Greenland Survey Bulletin, 176, 50-54. https://doi.org/10.34194/ggub.v176.5061
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The SIGMA project (Seismic Investigation of the Greenland MArgin) was designed to make accurate measurements of crustal thickness, velocity structure and seismic reflectivity along the hotspot-influenced volcanic rifted margin (VRM) off South-East Greenland (Fig. 1). SIGMA is a joint project between researchers at Woods Hole Oceanographic Institution (Woods Hole, Mass., USA) and the Danish Lithosphere Centre (DLC), and data was acquired on a cruise with R/V Maurice Ewing in August–October 1996. VRMs are characterised by a prism of igneous rocks that occupies the continent–ocean transition zone in an 80 to 150 km wide belt, several times thicker than normal oceanic crust, and which extends in some regions for more than 1500 km along strike. This thick igneous crust has two characteristics on seismic data: a seawarddipping reflector sequence (SDRS) interpreted as subaerially erupted basalt flows and intercalated volcanoclastics, and a high-velocity lower crust with P-wave velocities (7.2–7.6 km/s) suggestive of mafic to ultramafic intrusive rocks (Hinz, 1981; Mutter et al., 1982, 1984, 1988; Larsen & Jakobsdóttir, 1988; White & McKenzie, 1989; Holbrook & Kelemen, 1993). Several models for the thermal and mechanical processes involved in the formation of VRMs have been proposed, including: decompression melting during passive upwelling near a mantle plume (White & McKenzie, 1989); actively upwelling plume heads impinging on the base of the lithosphere (Richards et al., 1989; Duncan & Richards, 1991; Griffiths & Campbell, 1991); enhanced upper mantle convection driven by steep, cold lithospheric edges adjacent to the rift (Mutter et al., 1988) and hot upper mantle due to non-plume ‘hot cells’ or insulation by supercontinents (Gurnis, 1988). SIGMA consists of four transects systematically sampling the structure of the South-East Greenland margin and the continent–ocean transition at increasing distance from the Iceland hotspot track, in order to investigate the South-East Greenland VRM with respect to the following questions:1) What is the structure of the transition from continental to thick igneous crust, and thence to normal oceanic crust? Is the transition abrupt or gradual? To what extent does faulting play a role? Does the abruptness of the continent–ocean boundary change with distance from the Iceland plume? 2) What was the total volume of magmatism during continental breakup on the South-East Greenland margin and its conjugates, and how does it vary in space and time? How does this magmatism relate to distance from the Iceland plume and to its temporal magmatic budget? What is the proportion of plutonic to volcanic rocks, and how does this vary with distance from the hotspot track and with total crustal thickness? 3) Does high velocity lower crust exist beneath the margin, and if so, is there any evidence that its composition, thickness, and distribution change along strike? How might such changes relate to variations in melting conditions (temperature and degree of melting) with distance from the plume? 4) Is the structure of the South-East Greenland margin symmetrical with its conjugate margins on the Hatton–Rockall Bank and Iceland–Faeroes Ridge? What combinations of pure shear and simple shear processes might explain the conjugate structures?