TESTING GLACIALLY INDUCED LANDSCAPE TRANSIENCE; GLEN SHIEL AND THE MAMORE RANGE, NW SCOTLAND

Glacial erosion is generally considered an effective means of exhuming rock and reshaping topography. However, diverse controls on landscape development in glaciated mountain ranges, such as glacier type, ice basal temperature, ice thickness, and tectonic uplift, can impact the efficiency of glacial processes. Glen Shiel and the Mamore Range in the highlands of northwest Scotland display obvious glacial topography and are ideal locations for studying the controls and impacts of glaciation on denudation. We investigate these controls by determining under what conditions Quaternary glaciation led to increased denudation by comparing erosion rates over glacial (10^3-5 years) and tectonic timescales (10^5-7 years). Tectonic processes in Scotland are limited and previous apatite fission track studies from nearby regions of Scotland, which exhibit less alpine development then the current study area, report slow background exhumation rates of 0.004 mm/yr (Persano et al., 2007) and 0.015 mm/yr (Thomson et al., 1999). Scotland experienced ice-sheet glaciation throughout the late Cenozoic culminating in the Younger Dryas Stadial at 12.5 ka. In the highlands there is evidence for cirque glaciation and selective linear erosion. We use ¹⁰Be terrestrial cosmogenic nuclides on both sediment and bedrock to measure basin-wide and in situ erosion rates coincident with late Cenozoic glaciation. These rates will be compared to long-term exhumation rates determined from apatite (U-Th)/He thermochronometry. So far we have measured basin-wide erosion rates from 13 catchments to be 0.10-0.22 mm/yr (n=22). These exceed the short term rates measured from bedrock surfaces on ridges of 0.038-0.052 mm/yr (n=6), suggesting relief production via glacial erosion. A lack of correlation between basin-wide rates and catchment area, average slope, and sediment storage conditions, despite large variations among basins, imply that the rates could faithfully represent erosion despite technically violating basin-wide calculation assumptions requiring steady state conditions. A comparison of glacial to long-term erosion rates will reveal whether landscape transience was ubiquitously induced in response to a glacial climate and further quantify the thresholds for accelerated erosion in glaciated mountain settings.