1. 1. Amberrose Thornton Field Assignment Geology 103 Professor Lawler Spring Term 2014 Lake Tahoe A brief geological history of the Lake in the Sky Photo: A. Thornton, 2015
2. 2. Contents Introduction Geological Formation of the Lake DL Bliss State Park Eagle Rock McKinney Bay Rock Identification Flora and Fauna of the Lake Tahoe Basin Current Status of the LakePhoto: A. Thornton,
3. 3. Introduction I chose to do my field study about Lake Tahoe, in particular the west shore area because I live and work here. It was really interesting getting to learn a little more about area that I have been living in through this project. Lake Tahoe has a very fascinating history through all aspects of its existence. From its formation, to its first human inhabitants, to its present day state of existence. The geological history the small area that I decided to study for this project has inspired me to learn more.
4. 4. The Formation of Lake Tahoe 4 million years ago, the upward thrust of surrounding mountains and the downward fall of the valley bottom along these faults and formed a basin that created an ancestral lake. 3 million years ago, etupting volcanoes created a volcanic dam, which blocked the water outlet that is known as the Truckee River, causing a much larger
5. 5. The Formation of Lake Tahoe Eventually a new outlet was eroded from the lava dam creating the present path of the Lower Truckee River. Following the faulting and volcanic period of the Basin, an Ice Age developed. Huge glaciers formed and moved down the V-shaped canyons on the western side of the lake. These glaciers scoured away loose rock and reshaped the canyons into broad U-shaped valleys. The rock and gravel left behind at the sides and end of these melting glaciers are called moraines. As these glaciers melted away, they also left behind brilliant bays, jagged peaks, glacial polished ridges and crystal clear lakes (USDA, n.d) Tahoe is an ancient lake and at 2-3
6. 6. Chambers Landing Homewood Ski Resort View of McKinney Bay as seen from Eagle Rock Photo: A, Thornton, 2015 Between 7-15 thousand years ago, an underwater earthquake likely triggered a massive four-mile long underwater landslide on the West Shore This landslide widened the lake by three miles, pushed debris nine miles out into the lake and generated a catastrophic 300 ft. high tsunami (Antonucci, 2011) McKinney Bay
7. 7. McKinney Bay Landslide Video: Ward, S. n.d
8. 8. Eagle Rock Eagle Rock is a phreatomagmatic volcanic vent that erupted through gravels that were either water saturated or in shallow lake water. It is composed of basaltic tuff breccia with angular to rounded fragments of scoriaceous black basalt up to 50 cm, and sparse accidental clasts of andesite boulders and cobbles. Inward-dipping stratification indicates intra-vent deposition. There is a correlation of basalt at Eagle Rock with Pleistocene flows that are widespread in areas near Tahoe City evidence that Eagle Rock was overridden by glacial ice and partially buried beneath moraines during Tahoe and possibly Tioga glaciations of Blackwood Canyon. Here, at the mouth of the canyon, numerous glacial erratics lie on top of Eagle Rock, including granodioritic boulder
9. 9. Eagle Rock
10. 10. DL Bliss State Park
11. 11. Rock Identification
12. 12. Flora and Fauna of the Lake Tahoe Basin
13. 13. Flora and Fauna of the Lake Tahoe Basin
14. 14. Current Status of the Lake
15. 15. Sources Schweickert, R., Lahren, M., Hawle, J., & Kortemeier, W. (n.d.). Retrieved June 23, 2015, from http://foundation.aapg.org/documents/Field_Trip_Presentation.pdf Ward, S. (n.d.). Lake Tahoe Shelf Collapse Video. Retrieved June 19, 2015, from http://es.ucsc.edu/~ward/