Date of Award:

8-2020

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

Tammy Rittenour

Committee

Tammy Rittenour

Committee

Justin DeRose

Committee

Joel Pederson

Committee

Joe Wheaton

Committee

Patrick Belmont

Abstract

Most streams in the southwestern United States do not flow all year, and given their delicate balance of sediment and water flow, they are sensitive to climate change. At the turn of the 20th century, many streams in the Southwest rapidly incised into their floodplains, forming arroyos with a channel entrenched into near-vertical channel banks mostly composed of sand and mud. This dissertation investigates past changes in watersheds draining the Grand Staircase region in southern Utah with the goal of understanding how changes in climate and sediment influence these types of streams. Results show sediment supply is highly variable across the study area because of different rock types and slope, with hotspots of erosion located along the White and Pink Cliffs. This conversely leads to sediment storage on low-relief benches and valleys. Fast rates of erosion and large amounts of sediment cause channels to be overloaded with sediment and unstable over time. This dissertation supports the hypothesis that channel entrenchment is caused by a combination of climate changes and internal-thresholds that control the stability of the channel. The role of climate and fire in this landscape is investigated, and results support the idea that the frequency and intensity of drought and its effect on vegetation have influenced fire activity over the past millennia.

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