The shore along this section of Lake Tahoe has short cliffs of basaltic lapilli tuff. A tuff is volcanic rock that is formed of material ejected during an eruption. It is often hot enough to weld back together when it lands. Lapilli describes the size of the fragments, 2 to 64 millimeters in diameter. And basaltic describes the composition of the fragments, a rock composed of plagioclase feldspar and pyroxene.
The formation shows distinct layering that dip toward the lake. These layers likely represent multiple volcanic events and/or fluctuations in the intensity of the same eruption. It is possible that these layers were deposited on the sides of a volcanic cone, so they have always had some tilt to them. The layers extend offshore about 1 kilometer.
At the east end of the beach there are pillow lavas. These volcanic rocks form as hot lava comes into contact with water. This indicates that the eruptions occurred under water or flowed into the water. The timing of the eruptions, 0.92 to 2.0 million years ago, indicate that the water was from a lake present in the area before the current lake had formed, thus the name prototahoe.
Logging requirements:
Send me a note with :
- The text "GC42QG0 Skylandia Beach Lapilli Tuff" on the first line
- The number of people in your group (put in the log as well).
- What is angle of the layers at this location?
- Do you see the layers extending off shore, why or why not?
- Do you agree with the classification of the rock as lapilli? Explain.
The above information was compiled from the following sources:
- GEOLOGY OF THE LAKE TAHOE REGION, CALIFORNIA and NEVADA September 9, 2011 Fieldtrip for AAPG Foundation Trustee Associate 34th Annual Meeting Truckee, California Richard A. Schweickert, Mary M. Lahren, Jim Howle, and Winnie Kortemeier, Emeriti, Department of Geological Sciences, University of Nevada, Reno, USGS, Western Region Remote Sensing and Visualization Center, Carnelian Bay, California, Western Nevada College, Carson City, Nevada