Between 23,000 and 12,500 years ago Mono Lake was quite a bit larger and deeper than it is today. During the Tioga Glaciation, multiple glaciers originating in the Sierra Nevada drained into this ancient lake that has been named Lake Russell. This lake was approximately 10 times deeper and 5 times larger than the current one.
About 13,300 years ago a surtseyan or phreatomagmatic eruption occurred. This type of eruption occurs when magma (or lava) encounters groundwater or surface water. These types of eruptions are typically violent as the water flash boils and explodes. In this case, two vents erupted basaltic lava beneath Lake Russell.
The eruption formed a tuff cone at the bottom of the lake. The erupting material cooled quickly into tiny particles called ash, very small glass like particles, not the material left over after a fire. This material built up around the vents in a cone. When the eruption ceased, the basalt ash began to cool and consolidate. The cooling caused the cone to contract. To accommodate the contraction, large fissures formed. The settling and consolidation of the ash may have also created fractures that helped create and/or enlarge the fissures.
Logging questions:
- The text "GC3KKER Black Point – The Underwater Volcano" on the first line.
- The number of people in your group (put in the log as well).
- Enter one of the fissures and look for layering in the cone. Describe what you see.
- Do the fissures have a general pattern, are they all aligned the same way?
- Describe the size of the ash particles in the side of one of the fissures?
The following sources were used to generate this cache.
- National Forest Service informational panel
- USGS Panum Crater, http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/panum_crater.html
- Renee Murdock, June 17, 2004, Geology of the Sierra Nevadas, Mono Basin Volcanism USGS Volcano Hazards Program, Long Valley Observatory, http://lvo.wr.usgs.gov/gallery/30714277-001_caption.html