First Advisor

Adam M. Booth

Term of Graduation

Fall 2020

Date of Publication

1-13-2021

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geology

Department

Geology

Language

English

Subjects

Debris avalanches -- Southeast Alaska, Soils -- Carbon content -- Southeast Alaska, Sedimentation and deposition, Carbon sequestration, Landslides -- Southeast Alaska

DOI

10.15760/etd.7506

Physical Description

1 online resource (v, 53 pages)

Abstract

Forest disturbances in the form of landslides mobilize carbon (C) sequestered in vegetation and soils. The mobilized C has two basic depositional fates, deposition onto hillslopes or into water, which sequester C from and release C to the atmosphere at different time scales. The C-dense old-growth temperate forests of SE Alaska are a unique location to quantify the C mobilization rate by frequent landslide events. In this study, we estimate the amount of C mobilized by debris flows over historic time scales by combining a landslide inventory with maps of modeled biomass and soil carbon. We then infer depositional fate over geologic time scales via simulated debris flow deposition modelling with DFLOWZ, calibrated to the study area. In August 2015, a single storm initiated 66 debris flows near Sitka, AK and mobilized 57,651 ± 3,266 tC, while historic storms over a 55-year period in SE Alaska mobilized a total of 4.69 ± 0.21 MtC. Approximately 21% of historic debris flows intersected the stream network, which was consistent with long-term modeled connectivity and suggests that debris flows likely contribute to measured high dissolved organic C in streams and globally significant amounts of C buried in local fjord sediments. Moderate landslide frequency in areas with high C density mobilized C at the highest rates. Our results are consistent with an emerging consensus that disturbances which mobilize organic carbon may play an important role in the global carbon cycle over geologic time, in addition to geochemical processes such as silicate weathering.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Comments

This project received funding from NSF Award EAR-1711986.

Persistent Identifier

https://archives.pdx.edu/ds/psu/34681

782145_supp_a2cbbf35-ded4-4ed8-aa12-f45756e31cbd.csv (330 kB)
MeasuredLandslideCarbon.csv

Available for download on Thursday, January 13, 2022

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