At the end of Lake Mary Road there is a day use parking area at Horseshoe Lake along with restroom facilities. At the parking area you will notice the fading danger signs warning of excess carbon dioxide in the area. The signs caution you that if you feel light headed or nauseous at any time leave the area immediately. While the carbon dioxide quickly dissipates in the atmosphere, it is hazardous to dig holes in and around areas where the trees have been killed by carbon dioxide gas. Summer-time exposure to high levels of CO2 in the Horseshoe Lake area may result from lying directly on the ground or digging pits in the ground. Walking through the area in the summertime is safe for children and dogs, as long as their heads stay above ground level. During the winter, CO2 levels can build up beneath the snowpack and the CO2 gas will preferentially escape around buildings, through tree wells, and through depressions around large rocks. Such areas should obviously be avoided, as should snow camping within tree-kill areas
While plants produce oxygen from carbon dioxide and sunlight, they still need oxygen to utilize the sugars they make in order to survive, especially the roots where there is no photosynthesis. Areas outside the tree kill area, concentrations of carbon dioxide in the soil are less than 1 percent. After the earthquake swarm in 1990 , carbon dioxide concentrations in the soil increased to 20 to 90 percent over about 170 acres. This concentration of carbon dioxide killed the trees.
The carbon comes from either from degassing from magma or the release of the gas from limestone as it is metamorposized by magma or a combination of each. It is likely that the earthquake swarm was caused my magma moving underneath Mammoth Mountain.
Magma has carbon dioxide dissolved in it. As the magma moves up in the crust there is less pressure on it allowing dissolved gasses to escape (this is the same process that releases carbon dioxide from carbonated drinks when they are opened).
The magma could have also come into contact with various limestone rich rocks beneath Mammoth Mountain. As limestone (CaCO3) is heated, carbon dioxide (CO2) is released.
The carbon dioxide makes it way to the surface along fractures in the rocks. The map to the right shows the amount of carbon dioxide coming out of the ground in this area. The red areas have the most carbon dioxide.
Studies of the chemical and isotropic (elements with different weights) composition of the carbon dioxide suggest that a single large resevoir of carbon dioxide exists beneath the mountain.
Logging questions:
- The text "GC3JK03 Horseshoe Lake Tree Kill" on the first line.
- The number of people in your group (put in the log as well).
- What areas do you see that would collect CO2 and be dangerous?
- Based on the health of the trees at the edge of the dead area and or in the dead area, is do you think the CO2 is continuing to kill the trees?
- Does the forest service still consider the area dangerous? What gives you that idea?
The following sources were used to generate this cache.
- Carbon Dioxide and Helium Discharge from Mammoth Mountain, USGS Volcano Hazards Program, Long Valley Observatory http://lvo.wr.usgs.gov/CO2.html and http://volcanoes.usgs.gov/Imgs/Jpg/LongValley/30210600_004_caption.html
- Invisible CO2 Gas Killing Trees at Mammoth Mountain, California, Reducing the Risk From Volcano Hazards, USGS