← Back to Gallery

Shaking Evidence Near the Epicenter of the 1964 Great Alaska Earthquake at Allison Lake, Alaska USA

Proximal to the epicenter of the 1964 M_w9.2 Great Alaska Earthquake, Allison Lake contains a high-resolution, sedimentary archive of deposits that record >4000 years of past earthquake shaking. Located in Alaska's Chugach Mountains above Port Valdez and Prince William Sound (PWS), the 58-m-deep lake is fed by a glaciated, high-precipitation watershed. The Allison Glacier covers 20% of the watershed and supplies the lake’s primary inlet stream and voluminous fine-grained sediment across a broad fan delta.
Sediment cores collected in the lake between 2006–2010 revealed annual laminations of silt and clay (varves) with thicknesses that correlate with regional precipitation records. Varve counting and the 1963 peak in ¹³⁷Cs activity suggest that a 5-cm-thick graded turbidite records 1964 earthquake shaking. In 2023–2024, we returned to the lake to investigate evidence of older earthquakes and acquired lake-wide, multibeam bathymetry, sub-bottom chirp profiles, additional short (<2m) percussion-driven gravity cores, and a 13-m long composite piston core collected with a Uwitech platform. Chirp data resolve multiple large-volume, mass-transport deposits beneath the lake floor that correlate with 8-10 thick (5–40 cm) megaturbidites in the composite core. CT-scanning, XRF intensity, grain-size and multi-sensor core logger data characterize lake sediment properties. Three sub-facies distinguish the thick, gray megaturbidites from thinner (<5 cm) gray and brown turbidites: 1) basal normally-graded sand overlain by 2) light-grey silt and clay that is capped by 3) millimeter-scale silt-clay lamina. Varve counts, tephrochronology, radionuclide and radiocarbon dating inform an age-depth model that spans the past 4400 calendar years before 1950. This interdisciplinary analysis aims to differentiate seismically triggered deposits from flood-related sedimentary features in Allison Lake. Ongoing work focuses on comparing the lacustrine paleoseismic record of Allison Lake with submarine landslide evidence from nearby Port Valdez and to reexamine the regional paleoseismic history of the eastern Alaska-Aleutian subduction zone.

Session: Subaqueous Evidence for Earthquakes, Coseismic Landslides, Tsunamis and other Cascading Hazards [Poster]

Type: Poster

Room: Exhibit Hall A+B

Date: 4/15/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Robert Witter

Student Presenter: No

Invited Presentation: 

Poster Number: 167

Additional Authors