April Meeting

Tuesday • April 16th 2019 • 6 – 9 PM

Old Market Pub & Brewery 6959 SW Multnomah Blvd, Portland, OR 97223

6 PM — Social Hour

6:45 PM — Dinner

7:30 PM — Presentation

Dinner pricing is as follows:

$25 – Private Industry • $20 – Public Agency • FREE for students

*There is a $2 surcharge for those who do not reserve by the deadline

Reservations can be made here: RSVP by 12 PM Monday, April 15th

Hunting for Cascadia Triggered Landslides

Speakers: Bill Burns and Will Struble

Large magnitude earthquakes and climatic events in mountainous settings commonly trigger thousands of landslides, and these slope failures typically constitute a significant proportion of the damage associated with these events. Large, dormant deep-seated landslides are ubiquitous in the Oregon Coast Range (OCR), USA, yet a method for calculating landslide ages with accuracy required to diagnose a specific triggering event, including the 1700 AD Cascadia earthquake, has remained elusive. Establishing a compelling connection between pre-historic slope instability and specific triggers requires landslides ages with accuracy greater than that provided by 14C dating of detrital materials. Tree ring analysis is the only known method capable of determining landslide age with this accuracy. Dozens of landslide-dammed lakes in western Oregon present an opportunity to use tree rings from drowned snags, or ‘ghost forests,’ to establish the year of death, and thus landsliding. We crossdate tree ring indices from drowned Douglas-fir trees with existing live tree ring records from the OCR that exhibit synchronous, time-specific patterns due to regional climate variations. Our analyses determine that the landslides responsible for creating Wasson and Klickitat Lakes occurred in 1819 and 1751 AD, respectively. 14C dates from selected tree rings and landslide deposit detritus are consistent with our tree ring analysis, although the ages exhibit high variability, revealing the limitations of using 14C dating alone. Because dendrochronology provides annual accuracy of landsliding, sampling tree rings at additional landslide-dammed lakes throughout the OCR can be used to constrain the potential effects of ground motion and major climatic events on Cascadia landscapes.

Speaker Bio: Bill Burns, MS, CEG

Bill attended Florida State University where he earned his bachelor’s degree in geology and then Portland State University for his master’s degree in geology.  While working on his masters, he was a research assistant on a study of landslides impacting the Portland METRO from the storms of 1996-97.  His master’s thesis was on the Engineering Geology and Relative Stability of an area in Oregon City, Oregon.

Bill is a registered Professional Geologist (RPG) and Certified Engineering Geologist (CEG) in Oregon and Washington.   He spent roughly 10 years consulting as an engineering geologist in Oregon and Washington before his current position as Landslide Geotechnical Specialist at the Oregon Department of Geology and Mineral Industries (DOGAMI).  He has spent the last 15 years at DOGAMI working on research related to earthquake, landslide, and volcanic hazards in Oregon.  He is the principal investigator at DOGAMI on landslide hazards and has authored many publications on landslide hazard mapping methodology, risk analysis, and maps. He has spent the last 25 years helping communities in Oregon understand and reduce risk from earthquake, volcano, and landslide hazards.  Bill is also an active member of the Association of Engineering Geologist (AEG) and the Geological Society of America (GSA).

Speaker Bio: Will Struble

Will Struble is a PhD Candidate in the Department of Earth Sciences at the University of Oregon. As a native of northern Nevada and Lake Tahoe, his fascination with landscape evolution stems from exploring the Sierra Nevada and Basin and Range at a young age. His research focuses on quantifying landscape response to seismicity in the Pacific Northwest, notably by dating landslide-dammed lakes in the Oregon Coast Range using dendrochronology. He additionally is studying the tectonic geomorphology of the Cascadia forearc over Neogene timescales. He received his BS in geology from the University of Nevada, Reno in 2016 where he worked on using the geomorphic expression of normal faults to predict slip rate. He is a recent recipient of the Lokey Doctoral Science Fellowship, and he spent summer 2018 at the University of Potsdam working on landscape evolution numerical methods. When not perusing Oregon’s ever-growing LiDAR dataset, he spends his time hiking and exploring the western U.S.

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