Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 41-1
Presentation Time: 9:00 AM-3:30 PM


KINGEN, Kara, Geology, Portland State University, 4825 N Lombard, Apt A, Portland, OR 97203, LESHCHINSKY, Ben, Forest Engineering, Resources and Management, Oregon State University, 273 Peavy Hall, Oregon State University, Corvallis, OR 97331 and BOOTH, Adam M., Geology, Portland State University, 1721 SW Broadway, Portland, OR 97201

Slow-moving earthflows represent major sources of sediment transport and erosion, and tend to be problematic for the management of major roads and highways. The Hooskanaden earthflow (HEF), a slow-moving earthflow located in southwestern Oregon, has been a site of particular interest to the Oregon Department of Transportation (ODOT), due to its proximity to US Highway 101, weak underlying lithology, and net erosive environment. Despite having been studied all over the world for decades, relationships among climate, seismicity, and base level controls on the initiation, motion, and spatial distribution of earthflows are still poorly constrained. This lack of understanding, and their long-term evolution over decades and centuries makes earthflow behavior difficult to predict. While it is understood that seasonal changes in precipitation can be a major driver in earthflow motion, less is known about the potential influences of long-term climate cycles, such as El Nino Southern Oscillation (ENSO) or Pacific Decadal Oscillation (PDO). I hypothesize that, like other earthflows in similar lithologic and climatic environments, the HEF is primarily driven by increased pore pressure, and is therefore impacted by both short-term (seasonal) and long-term (decadal) climate cycles. To address this, a time series will be created to reconstruct a history of surface velocities along the HEF. Preliminary data sets are available via drilling performed by researchers at ODOT and Oregon State University. Inclinometer results clearly show the failure plane between 35m and 40m depth. While piezometers sheared too quickly to yield viable data on subsurface water, the time and distance over which they sheared indicates an average velocity of 1-5 m/yr. Initial 14C dates calibrate to likely within the last ~300 years. By performing manual feature tracking on orthorectified historic aerial photographs (3-7 years apart from 1977-2002), and modern satellite imagery (~weekly from 2009 to present), I intend to address the existing gap in timescales by comparing changes in HEF surface velocity to local climate data, in order to examine the effects of both short-term and long-term climatic cycles. Higher velocities are expected to follow periods of intense or prolonged rainfall, and will likely coincide with cold ENSO and PDO phases.