← Back to Sessions

Lidar Analysis of an Elevated Marine Terrace Along the Olympic Peninsula, Washington State, USA

Description: 

Lidar reveals subtle geomorphic features in regions of dense vegetation, making it particularly useful along the forested coastlines of the Pacific Northwest. We use a bare-earth surface model derived from lidar to analyze a prominent terrace along the coastal extent of the Cascadia subduction margin in the western and northern Olympic Peninsula, Washington State, USA. The terrace extends discontinuously for ~150 km from Queets to the southern shoreline of the straits of Juan de Fuca. The geomorphic expression of the terrace is clear, displaying an even and undissected surface, a prominent front edge forming the modern rapidly eroding seacliff, and a backedge inset into high landslide-dominated bluffs. In most places, the bluffs mark the eroded edge of an extensive glacial till plain, with glacial flutes extending to within a few meters of modern sea level. Terrace geomorphic backedge elevations derived from lidar and confirmed by GNSS RTK measurements vary from ~4-8 m NAVD (North American Vertical Datum 88). Outcrop observations and test pits near Point Alava establish the marine origin of the deposits forming the terrace, which is underlain by an elevated marine abrasion platform capped by cobble grading into well sorted beach sand. The location, sedimentology, and geomorphology of the terrace are most simply explained as an elevated and abandoned beach complex. The lack of more than one conspicuous terrace surface suggests that terrace abandonment happened suddenly, consistent with a tectonic rather than glacio-isostatic origin. Future work will include testing predictions of fault deformation models against the distribution of terrace uplift values to discriminate between subduction and upper plate sources.

Session: The Landscape Record of Earthquakes and Faulting [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Rich

Student Presenter: No

Invited Presentation: 

Poster Number: 4

Authors