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Valley and moraine morphology as a function of lithology and surficial processes on Tana Volcano, Islands of Four Mountains, AK
Lanman III, Henry R.
May 11, 2016
The east Tana valley hosts one of the last remaining glaciers in the Islands of Four Mountains (IFM), AK. The valley has the most dissected and glacially sculpted valleys in the IFM. Moraine mapping, analysis of the hydrothermally altered rock, and valley morphology analysis, show that the presence of hydrothermally altered rock affects both valley morphology and moraine morphology. Most glacial ice in the IFM and nearby islands is located on north facing aspects, whereas the east Tana valley is on an east-northeast facing aspect. This is likely due to a pre-Last Glacial Maximum sector collapse and enhanced glacial erosion in soft hydrothermally altered rock. Little Ice Age moraine slope, diffusivity, and relief are a function of rock type and geomorphic location. First, moraines composed of heavily hydrothermally altered rock that have high crests and long proximal slopes have low diffusivities and high slope angles, ranging from 9.13 x 10⁻⁵ and 1.1 x 10⁻⁴ m²/year and between 41.3 and 60.2 degrees, respectively. Second, moraines composed of heavily hydrothermally altered rock that have relatively low crests and short proximal slopes have high diffusivities and low angles. These moraines have diffusivities between 5.5 x 10⁻³ and 4.8 x 10⁻⁴ m²/year and slopes between 33.0 and 55.3 degrees. Finally, moraines composed of relatively unaltered rock show low diffusivity and low angle. The one moraine composed of relatively unaltered rock showed a diffusivity of 4.7 x 10⁻⁶ m²/year, and a proximal slope angle of 35 degrees. Thin-section and scanning electron microscopy analysis shows that heavily hydrothermally altered rock contains high abundances of clay constituents. We conclude that large amounts of hydrothermally altered clay, filling pore spaces within a moraine, in conjunction with compaction from the glacier due to confining pressure, increases strength and facilitates the steepening of moraines composed of heavily hydrothermally altered rocks. Thus, morphology of Little Ice Age moraines in the proximal moraine complex is primarily controlled by lithology and compaction from the glacier. Additionally, the correlation of moraines and relative dating indicate there were two advances during the Little Ice Age in the Islands of Four Mountains.
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