| It is commonly inferred that alpine glaciers transform fluvial valleys from V to U-shaped. It has been suggested that, under certain circumstances, glaciers are unable to modify V-shaped valleys and that lithology may play an important role in a glacier's ability to effectively erode bedrock. To test this hypothesis, six glaciated valleys with both U and V-shaped cross sections were chosen in the Sierra Nevada (CA) to examine how lithological properties might affect patterns of glacial erosion: Tenaya Canyon, Tuolumne River, Little Yosemite Valley, the San Joaquin River, the north fork of the King River, and Deadman Canyon. Valley profiles were fitted with the power law, y = axb, where the exponent b represents the shape of the cross section. Rock mass strength (RMS) values for these sites were determined by field inspection. No clear relationship was found between RMS and valley shape. Although, there was a weak association between measured joint orientation and valley axis in Little Yosemite Valley, the North Fork of the King River, and the San Joaquin, the two variables appear unrelated in Tenaya Creek, Tuolumne River, and Deadman Canyon. These results propose that in the Sierra Nevada granitic batholith, patterns of glacial erosion in granitic rock are not dependent on rock mass strength (as typically measured), while joint orientation may play a minor role. |
