Academic literature on the topic 'Lahars – Oregon – Hood, Mount, Region'

Abstract The Sierra Nevada red fox Vulpes vulpes necator is a native subspecies associated with subalpine regions in the Sierra Nevada and Cascade mountain ranges of California and Oregon. In the past century, the Sierra Nevada red fox experienced a major range contraction and decline in California. However, the number, size, and connectivity of populations extant in Oregon remain unclear. This knowledge gap impedes efficient monitoring and hinders development of a cohesive conservation strategy for the subspecies. The historical range is large and includes rugged terrain with low accessibility; therefore, a predictive model is needed to facilitate more comprehensive and systematic surveys in the future. We initiated a multiagency collaborative effort to survey portions of the range in the Oregon Cascades during 2011–2016 (verified genetic and photographic detections) and to assemble existing sighting reports dating back to 1985 (unverified), which we used to create Maxent models to predict the potential distribution of Sierra Nevada red fox within Oregon. To identify optimal levels of model complexity, we compared cross-validation accuracy of models that varied in levels of protection against overfitting (regularization). The highest-performing models utilized intermediate regularization, and included minimum January temperature and land-cover type. Regardless of regularization or data set (verified detections, all putative detections), all models agreed in predictions of a high-probability region covering approximately 3,470 km2 or 6% of the Cascade region, corresponding to the high-elevation portion of the crest. With the exception of a gap between Mount Hood and Mt. Jefferson, this core area of predicted presence was continuous along the north–south extent of the crest, suggesting a capacity for high connectivity among observed clusters of occurrence. Use of modeled potential distributions in future survey design will improve efficiency of field data collection, facilitating more precise evaluations of the distribution, abundance, and genetic integrity and connectivity of Sierra Nevada red fox in Oregon.

Over a span of six days from November 2-7, 2006 approximately 43 cm of precipitation fell over the Hood River Basin in Oregon. A lahar was initiated on the Eliot Branch of the Middle Fork Hood River by two or more landslides that occurred on the lateral moraines of the Eliot Glacier on the early part of November 7th, 2006. The Eliot Branch lahar was embedded within the larger regional flood that was occurring in the Hood River Basin and traveled a total of 48 km from the initiation points on the north flank of Mount Hood to the Hood Rivers confluence with the Columbia River. The initiating landslides abruptly transformed into a debris flow upon mixing with flood waters of the Eliot Branch. The debris flow traveled a distance of ~28 km at which point it was transformed first to a hyperconcentrated flow and then to water flow via selective deposition of coarse sediment and progressive dilution by channel flow waters from the East and West Fork Hood Rivers. The transformation from debris flow to hyperconcentrated streamflow was recorded by a thickening wedge of hyperconcentrated streamflow sediments found above and below progressively fining debris flow sediments over a reach of 22 km. Finally, the hyperconcentrated-flow phase of the lahar transformed to water flow and then traveled an additional 20 km to the Hood River delta. Upon reaching the apex of the Hood River delta, depositing sediments led to an expansion of the delta. Debris-flow sediments were predominantly gravel (36.0-69.7% by wt.) with sand (22.1-55.9% by wt.) and fines (4.7-7.8% by wt.). Hyperconcentrated flow deposits contained a larger sand fraction of (66.8-99.2% by wt.) with few gravel clasts (0-26.0% by wt.) and fines (0-8.8% by wt.). Water flow deposits averaged 90.5% (wt.) sand with 6.0% (wt.) gravel and 3.0% (wt.) fines. Sorting was a key factor in flow identification and showed progressive improvement downstream from the initiation point. Sorting values for the flow types are as follows: debris flow deposits ranged from 3.3Φ (very poorly sorted) to 1.8Φ (poorly sorted), hyperconcentrated flow deposits ranged from 2.4Φ (very poorly sorted) to 0.8Φ (moderately sorted), and water flood deposits ranged between 1.4Φ (poorly sorted) to 0.6Φ (moderately sorted).

ABSTRACT The Mount Hood fault zone is a N-trending, ~55-km-long zone of active faulting along the western margin of the Hood River graben in north-central Oregon. The Mount Hood fault zone occurs along the crest of the Cascade Range and consists of multiple active fault segments. It is presently unclear how much Hood River graben extension is actively accommodated on the fault zone, and how Cascade intra-arc extension accommodates regional patterns of clockwise rotation and northwest translation of crustal blocks in the Pacific Northwest region of the United States. Evidence for Holocene activity on the Mount Hood fault zone was discovered in 2009 after acquisition of high-resolution lidar topography of the area. This trip will visit sites displaying evidence of Holocene surface rupture on fault strands within the Mount Hood fault zone. Day 1 starts with a two-hour drive from Portland to Mount Hood, a 3429-m-high glaciated active volcano, where we will visit sites south of the summit along the Twin Lakes fault segment, including several fault scarps and two sites where dating of offset buried soils constrains the timing of the most recent surface-rupturing event to the Holocene. Day 1 includes two hikes of ~1 km and will be partly cross-country. The trip will overnight at the historic Timberline Lodge, an architectural masterpiece from the Civilian Conservation Corps (1933–1942) era, located at tree line on the southern flank of Mount Hood. Day 2 will visit sites north of the summit, stopping along the Blue Ridge fault segment to view the site of 2011 paleoseismic trenches and an offset glacial moraine. We will visit an unusual uphill-facing scarp in coarse talus along the Gate Creek fault segment near the north end of the Mount Hood fault zone. We will conclude Day 2 with a short hike into the Mark O. Hatfield Wilderness along the Gate Creek fault segment to view evidence of a surface-rupturing earthquake that occurred only a few centuries ago, illuminated by a nearby paleoseismic trench hand-dug in 2020. Our neotectonic and paleoseismic data are among the first efforts to document and characterize seismic sources within the Mount Hood fault zone. However, even with our new age data, fault slip rates and earthquake recurrence remain poorly constrained. With our limited earthquake timing data, it is not clear whether all segments of the Mount Hood fault zone rupture together as a ≥ M 7 earthquake, or alternatively, if the fault segments rupture independently in a sequence of smaller ~M 6–sized events.