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Rate of accommodation space filling following the 1700 earthquake in an Oregon estuary: Extracting morphodynamic change from salt marsh stratigraphy

 

Primary Question: What is the timescale of accommodation space filling of Oregon high marshes following the rapid relative sea level rise created by the 1700 Cascadia earthquake?

During the 1700 earthquake, ≤ 3 m of co-seismic subsidence drowned marsh surfaces, and high-energy tsunami waves caused erosion and burial of the vegetated habitat. Lack of vegetation and its ability to trap sediment combined with increased wave and tidal erosion may have created a negative feedback, preventing reestablishment of high marsh for up to 150 years.

Alternatively, accommodation space was quickly filled through sediment accumulation and tectonic uplift, high marsh was re-established within approximately a decade. This is particularly feasible given the naturally high sediment loads within coastal Pacific Northwest rivers, and that shaking and destabilization of uplands may have provided an additional sediment pulse. Combined with rapid deposition, post-seismic rebound might also have led to rapid tectonic uplift, thereby contributing to quick re-establishment of marshes.

Motivation: Elucidation of land-ocean linkages and better ability to predict the impacts of tectonic and climatic perturbations to coastal geomorphology is of great importance. Mass transport through the coastal zone influences the physics, chemistry, and biology of marine systems thus altering global biogeochemical cycles. Analysis of stratigraphy leads to identification of landscape feedbacks, ranking of key drivers of change, and quantification of rates – critical in informing models of change.

Status: I am currently working with Tom Guilderson measuring a high-resolution age-depth model of the last 300 y using a combination of excess 210Pb and 14C data with funding from a Geological Society of America AGeS2 (Awards for Geochronology Student Research2) funding. I plan on presenting this research at GSA 2020.

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