Date of Award:

5-2021

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

Tammy M. Rittenour

Committee

Tammy M. Rittenour

Committee

Brian J. Yanites

Committee

Patrick Belmont

Abstract

Geologists often look at the Earth’s surface to understand the underlying processes that cause mountain formation. As tectonic forces drive uplift of Earth’s surface, processes of erosion transport sediment to lower elevations. Climate can play a large role in landscape formation as well as increased precipitation, accelerating rates of erosion. Rivers leave markers of landscape evolution through terrace landforms, former river floodplains that are left behind when rivers incise into a valley. To better understand landscape response to uplift, this research investigated the initial linkages between uplift, hillslope erosion (mass wasting) and river incision. At some point, it is thought that these three will be in equilibrium. Taiwan is a young mountain range making it the ideal setting to capture landscape development in the initial stages of uplift. I compare rates of river incision to rates of hillslope erosion and timing of terrace deposition to understand the links between erosion, tectonics and climate in the beginning stages of mountain building.

This thesis uses luminescence to provide age control for the last time sediment was exposed to light to determine when river terraces formed. Field mapping and observations allowed us to measure the height between terraces to quantify the rate at which streams incised. The results from this study show that the rivers of southern Taiwan are incising on average at a rate of 2.4 ± 1.2 meters per thousand years (m/kyr) with rates ranging from 6 ± 2.6to 0.2 ± 0.1 m/kyr. River incision rates and hillslope erosion (denudation) rates increase northward with drainage development suggesting that rates of erosion are primarily linked to tectonic forces on medium to longer-term scales (1,000-1,000,000 years) . Regional periods of terrace development occurred at 1, 11, 18, 28, and 40 ka. Periods of terrace development align with periods of increased East Asian Summer Monsoon (EASM) intensity chronicled in paleoclimate records. The EASM is the dominate weather pattern that delivers moisture to East Asia affecting 1/3 of global populations. Terrace deposits recording EASM intensity extends the record of landscape response to climate in Taiwan and reveals that climate signals can obscure tectonic forces on short-time scales (100 – 103 yrs).

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