Potential Triggering Mechanisms of Long-Runout Catastrophic Rock Avalanches in the Nooksack River Basin, Whatcom County, Washington
Research Mentor(s)
Clark, Doug
Description
The Cascade foothills east of Bellingham, WA in Central Whatcom County (Fig. 1) preserve a remarkable concentration of large rock avalanche deposits. These deposits present an excellent opportunity to test ideas related to potential triggering mechanisms (i.e., the causes) of such landslides. Though widely dated, common triggering mechanisms include ground accelerations during earthquakes, increased pore-water pressure from heavy precipitation events, or recent glacial or fluvial debuttressing of hillslopes. I examine each of these potential triggering mechanisms by determining landslide collapse ages through two independent dating methods: radiocarbon dating (14C) and cosmogenic radionuclide exposure dating (CRN). Collapse ages of these deposits are compared to known local or regional paleoseismic events (e.g., Cascadia Subduction Zone or Boulder Creek Fault ruptures; Fig. 2). For 14C dating, organic macrofossils (e.g. twigs, logs, seeds, etc.) were collected from sediment cores (Fig. 3) of bogs (e.g., Fig. 4 – C, E, D, H, I) formed on top of landslide debris fields. For CRN dating, rock samples were collected from the tops of large (> 3 m) boulders in boulder fields of each deposit (e.g., Fig. 4 - A, F, J) and will be analyzed at the University of Vermont - Community Cosmogenic Facility. If these rock avalanches were triggered by earthquakes, their ages should overlap with known paleoseismic events (Fig. 2). Conversely, other triggers should show different temporal distributions: glacial debuttressing should cluster immediately after deglaciation (Fig. 2), whereas precipitation triggering or fluvial debuttressing should display a more stochastic temporal pacing. To date (May 2020) we have collected 6 sediment cores, recovered 11 14C samples, and 9 CRN boulder samples. Unfortunately, the COVID-19 situation has delayed results for this study. We are awaiting the reopening of 14C-AMS facilities before more direct age control can be established.
Document Type
Event
Start Date
18-5-2020 12:00 AM
End Date
22-5-2020 12:00 AM
Department
Geology
Genre/Form
student projects, posters
Subjects – Topical (LCSH)
Landslides--Washington (State)--Nooksack River; Geomorphology--Washington (State)--Nooksack River
Geographic Coverage
Nooksack River Watershed (Wash.)
Type
Image
Rights
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.
Language
English
Format
application/pdf
Potential Triggering Mechanisms of Long-Runout Catastrophic Rock Avalanches in the Nooksack River Basin, Whatcom County, Washington
The Cascade foothills east of Bellingham, WA in Central Whatcom County (Fig. 1) preserve a remarkable concentration of large rock avalanche deposits. These deposits present an excellent opportunity to test ideas related to potential triggering mechanisms (i.e., the causes) of such landslides. Though widely dated, common triggering mechanisms include ground accelerations during earthquakes, increased pore-water pressure from heavy precipitation events, or recent glacial or fluvial debuttressing of hillslopes. I examine each of these potential triggering mechanisms by determining landslide collapse ages through two independent dating methods: radiocarbon dating (14C) and cosmogenic radionuclide exposure dating (CRN). Collapse ages of these deposits are compared to known local or regional paleoseismic events (e.g., Cascadia Subduction Zone or Boulder Creek Fault ruptures; Fig. 2). For 14C dating, organic macrofossils (e.g. twigs, logs, seeds, etc.) were collected from sediment cores (Fig. 3) of bogs (e.g., Fig. 4 – C, E, D, H, I) formed on top of landslide debris fields. For CRN dating, rock samples were collected from the tops of large (> 3 m) boulders in boulder fields of each deposit (e.g., Fig. 4 - A, F, J) and will be analyzed at the University of Vermont - Community Cosmogenic Facility. If these rock avalanches were triggered by earthquakes, their ages should overlap with known paleoseismic events (Fig. 2). Conversely, other triggers should show different temporal distributions: glacial debuttressing should cluster immediately after deglaciation (Fig. 2), whereas precipitation triggering or fluvial debuttressing should display a more stochastic temporal pacing. To date (May 2020) we have collected 6 sediment cores, recovered 11 14C samples, and 9 CRN boulder samples. Unfortunately, the COVID-19 situation has delayed results for this study. We are awaiting the reopening of 14C-AMS facilities before more direct age control can be established.