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Comprehensive High-Resolution Geophysical Mapping and Sediment Coring in Lake Chelan, Wa: A Deep, Steep Lacustrine Environment Dominated by Mass Transport Processes

Description: 

Lake Chelan (WA, USA), the third deepest lake in the contiguous United States, may hold records of glacial retreat and advance, volcanic eruptions, and earthquakes. For example, the 1872 Washington State Earthquake (M6.5–7) ruptured the Spencer Canyon fault near the southern end of Lake Chelan. Shaking from the 1872 earthquake was of such intensity that it altered local aquifers, triggered liquefaction of unconsolidated sediments, and large seiches within Lake Chelan. Lake Chelan may provide a geological dataset to calibrate the lake’s lacustrine sedimentary response to the 1872 earthquake. In 2023, the USGS conducted a 3-week field operation in Chelan to acquire high-resolution multibeam bathymetry data, Chirp sub-bottom profiles, and sediment cores. These new data reveal pervasive morphological evidence for slope failure, mass transport deposits (MTDs), subaqueous deltas, and relic glacial features (e.g., kettles). Here, we present preliminary results of detailed geomorphic and stratigraphic mapping throughout the lake. Chelan can be divided into two physiographic basins: the deeper (up to 460 m) and narrower (~2–3 km wide) Lucerne Basin to the north, and the shallower (up to 130 m), wider (5–10 km) Wapato Basin to the south. The Lucerne Basin is dominated by very steep flanks and subaqueous deltas fed by fluvial catchments; the depocenters are dominated by coarser-grained sediment and stacked MTDs. The Wapato Basin contains numerous slide scars, scarps, debris aprons along the gently sloping margins, and abundant kettle structures infilled with fine-grained lacustrine sediments. Sediment cores sampled several of the youngest MTDs; their relation to the 1872 earthquake is pending results of 14C and radionuclide dating. Furthermore, cores from condensed sections of the Wapato basin contain numerous ash deposits and bottom out in late Pleistocene glacial sediment. Our initial results suggest that Chelan contains several sources of MTDs, with the Lucerne Basin most affected by fluvial processes and the Wapato Basin being a better candidate for paleoseismic investigations.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Boe

Student Presenter: No

Invited Presentation: 

Authors