Life at the Limits: Earth, Mars, and Beyond

an educator workshop and fieldtrip

Horseshoe Lake Tree Kill

Reported by: Anna Coor, Billye Robbins, Melissa Snider

What we saw:

After baking and boiling ourselves at Hot Creek all morning, we drove up into the forested mountains in the Mammoth Lake area (shade at last!). As we rounded a bend in a high valley we saw a ghost forest of bare white trees at one edge of Horseshoe Lake. The surrounding forest looked green and normal.

Tree kill with healthy trees beyond
Healthy trees on the other side of the lake
Tree kill with healthy trees beyond
Healthy trees on the other side of the lake

The story:

In 1995 these trees and others in some nearby areas began dying. The biologically oriented Forest Service people suspected some sort of bug infestation until one poor soul almost died after entering an outhouse.

Further investigation revealed that CO2 was seeping up through the ground. The trees had suffocated!

Outhouse with warning (CO2 could be concentrated there.)
Stark, dead trees
Outhouse with warning sign (CO2 could be concentrated there.)
Stark, dead trees


Dr. Kiefer explained that magma contains large amounts of CO2. A magma chamber below the surface was disrupted by a series of earthquakes at the western edge of the Long Valley Caldera. This allowed CO2 to escape to the surface.

While plant leaves photosynthesize during the day, converting the Sun's energy, CO2, and water into oxygen and carbohydrates (sugars), roots are in the dark and do not photosynthesize. Instead, roots growing in the dark soil convert the sugars (made during photosynthesis) into energy that they can use; this is how they promote growth and stay healthy. This chemical process of converting the sugars to energy is called respiration, and it requires oxygen.

CO2 is heavier than oxygen. When the earthquakes caused CO2 to be released, it drove the oxygen out of the soil. The trees were unable to access oxygen at their roots. Unable to “breathe,” they died.

Extension questions:

We did not examine the soils in this spot. Is any microbial life present? If present, might it inform our investigation of other planets with CO2 -rich atmospheres? What implications are there for terraforming Mars, as it has a thin but CO2–rich atmosphere? Is there O2 in the soil on Mars?

For further information on the tree kill, visit the U.S. Geological Survey Fact Sheet 172-96.

For further information on respiration in plants, go to Plant Growth and Development.


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