2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 188-3
Presentation Time: 8:45 AM

EARTHQUAKE, LANDSLIDE, FLOOD?  THE WESTERN SNAKE RIVER SLIDE IN A TIME OF CLIMATE CHANGE


RUSSO, R.M., Department of Geological Sciences, University of Florida, 241 Williamson Hall, P.O. Box 112120, Gainesville, FL 32611 and MOCANU, Victor, Department of Geophysics, University of Bucharest, 6, Traian Vuia Street, RO-020956 Bucharest 2, RO-020956, Romania

We present new geodetic observations made since 2011 on a landslide developed on the south bank of the Snake River along the Oregon-Idaho border. Miocene-Pleistocene sediments deposited in glacial lakes are now eroding and sliding under semi-arid conditions. The slide area is ~3.9 km2; drilling by the Oregon Department of Transportation (ODOT) showed the failure surface lies at ~25-35 m depth near the Snake River, indicating that the sliding layer at greater elevation may attain a thickness of 200 m. The slide toe is submerged in the River, and ODOT personnel observed that high flow in the Snake River correlates with increased sliding, implying that high flow erodes the toe, facilitating slip. The slide is broken by differential motion into hummocky blocks characterized by crested culmination surfaces. Geodetic measurements from campaigns in August and October 2012, July 2013, and June 2014, yield horizontal velocities at three sites on the sliding units and one on the footwall near the crest of the elevated bluffs currently being scavenged by the slide. The footwall site moves ~1 cm/yr WNW, with respect to stable North America, similar to observed regional westward crustal movement due to Basin-Range extension. The site at highest elevation in the sliding material moves nearly due S at a rate of ~1.5 cm/yr, due to back rotation of a deforming block within the sliding mass. Two sites near the east end of the slide – one at high elevation and one near the Snake River – both move NE, but at 1 cm/yr and 2.2 cm/yr, respectively. Increased precipitation due to climate change, and notable seismic activity due to active extensional tectonics, both are concerns as they could singly or in combination lead to catastrophic failure. The slide is sufficiently voluminous to dam the Snake River temporarily, and the potential for a channelized wave topping the three hydroelectric dams now spanning the Snake along its Hells Canyon section cannot be ignored.

Session No. 188

T106. The Landslide Multi-Hazard Conundrum: What Primary Hazards Trigger Landslides, and How Do Landslides in Turn Cause Secondary Hazards?
Tuesday, 21 October 2014: 8:00 AM-12:00 PM
202/203 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.465
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