[ghsc-seminars] GHSC Seminar, TODAY, Thursday Nov. 29th @ 10am: Annette Patton, CSU, Landslide Initiation

[Rigler, Erin (Josh)]

*Spatial patterns of landslide initiation and development in the Colorado
Rockies and the Alaska Range*
*Annette Patton*
*Colorado State University *

We present the results of landslide investigations in Rocky Mountain
National Park, Colorado, and Denali National Park and Preserve, Alaska,
with methodological themes including analysis of the spatial distribution
of landslides, slope characterization, and landslide mapping. In both the
semi-arid Colorado Rockies and the discontinuous permafrost system of the
Alaska Range, key factors in landslide initiation include lithology,
convergent topography, and sediment production and supply.

During an extreme storm in the Colorado Front Range in September 2013, 11
debris flows initiated at high elevations in Rocky Mountain National Park.
Eight of the 11 flows initiated as small landslides in areas of convergent
topography, and eight initiated at elevations > 2800 m. Debris flows at
high elevations in the Front Range are atypical; this event broadens our
understanding of debris flow regimes in the Front Range. At one site with
evidence of multiple debris flows sourced from the same colluvial hollow,
we obtained relative ages of debris flow deposits through geomorphic
mapping and fan stratigraphy. We used beryllium-10 (10Be) analysis to age
stratigraphic deposits and debris flow levees. Large ranges in cosmogenic
exposure age and anomalously old samples indicate that sampled boulders (n
= 14) contained inherited 10Be concentrations. Despite this limitation,
10Be sample ages from all levees suggest that greatest sediment production
occurred during Quaternary glacial stages due to periglacial processes.
Subsequent evacuation of the colluvial hollow likely occurred during wetter
periods of the mid-Holocene.

Rapid permafrost thaw in the arctic and subarctic increases hillslope
susceptibility to landsliding by altering physical and hydrologic
properties of hillslope materials, including reduced cohesion and increased
hydraulic connectivity. We evaluate the fundamental processes that increase
landslide frequency in regions of permafrost thaw and the short term
topographic response of hillslopes to shallow-angle landslides. We
synthesize remote analysis with field methods including surficial geologic
mapping and time-series terrestrial lidar surveys of small (<1 km2)
landslides in Denali National Park and Preserve, Alaska. Notably,
landslides primarily occur in susceptible lithologies (unconsolidated
glacial deposits and weathered felsic volcanics) and on hillslopes with a
bimodal distribution of slope angles. These results suggest that permafrost
or ice-related processes are generating landslides on shallow angles, while
rainfall-dominated initiation occurs at steeper slope angles. These shallow
landslides result in topographic signatures that influence snow
accumulation for at least two years.


*Thursday, November 29th**, 2018*
*10-11a*
*m*
*  (Mountain Time)*
*USGS, 1711 Illinois Street, Golden, CO*
*Entry Level Seminar Room (204)*

*Note: Please arrive *~5 minutes early* and *bring photo ID* for
airport-style security measures now in place at the USGS building.

Thank you,
GHSC Seminar Committee

Ben
Mirus - bbmirus at usgs.gov
Josh Rigler - erigler at usgs.gov
Oliver Boyd - olboyd at usgs.gov <oboyd at usgs.gov>
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