The interaction of climate, tectonics, and topography in the Olympic Mountains of Washington State: the influence of erosion on tectonic steady-state and the synthesis of the alpine glacial history

摘要

The interaction of climate, tectonics, and topography in the Olympic Mountains of Washington State is explored to determine the influence of glaciers on spatially variable erosion and rock uplift rates. As glaciers have long been present on the peninsula, could glacial erosion explain the observed pattern of rock uplift? A numerical model of glacial flow, ICE Cascade, is used to reconstruct the glacial extent of the Last Glacial Maximum for the first time. Modeled ice extent best matches observations when summer temperatures range from 7.0-8.0°C and precipitation is reduced to 0.4-0.8 times the modern. These values are consistent with paleoclimate records. Simulated glacial erosion based on a sliding law varies with observed trends in rock uplift rates across the peninsula. If erosion rates are assumed to equal rock uplift rates, as suggested by evidence of tectonic steady state in the region, a glacial erosion constant on the order of 10-5 is indicated based on modeled sliding rates in three valleys on the western side of the range. These efforts are hampered by the lack of a glacial and paleoclimate record from the northern and eastern peninsula. A regional growth curve for lichenometric dating of neoglacial moraines is developed and applied to four moraines at the base of Royal Glacier on Mt. Deception. The moraines range in age from 1839±45, 1895±45, and 1963±45, to less than 20±45 years. The estimated equilibrium line altitude (ELA) for Royal Glacier during this time is 1774 m as compared with 1688 m for Blue Glacier in the western Olympics over the same period. A compendium of glacial deposits observed throughout the peninsula is also summarized so a broader picture of the alpine glacial extent and continental ice extent can be developed. Overall, this work demonstrates that the sliding based glacial erosion model can explain the uplift pattern when the glacial erosion constant is on the order of 10-5 in three separate river valleys. Additional work on the northern and eastern sides of the peninsula would allow for a broader picture of the glacial history and provide a closer glacial erosion constant in the model. The culmination of work in these areas allows for a greater understanding of how climate, erosion, and tectonics interact on the Olympic Peninsula.