Mammoth Mountain in the eastern Sierra Nevada mountains of California is a favorite destination for outdoor enthusiasts year-round. Surrounded by incredible scenery like the lakes in the Mammoth Lakes Basin, there are endless opportunities to get out and enjoy nature. But because of the geological history of the area, nature doesn’t always play nice.
The area around Mammoth Mountain has been formed by fire and ice. The Lakes Basin was carved by the activity of glaciers during the Tioga glacial event that lasted from about 25,000 years ago until 12,000 years ago. The glacier that carved the basin formed beneath Mammoth Crest, the spine of rock seen above Horseshoe Lake in today’s photo, and extending to the left out of the frame of the photo. This glacier carved depressions in the bedrock that are filled by some of the upper lakes in the basin. The lower lakes, including Horseshoe, Mary, Mamie, and Twin Lakes formed in depressions in glacial moraine deposits.
The beautiful features of the Lakes Basin are but geological newcomers compared to the forces of fire that shaped much of the rest of the area around Mammoth Mountain. The mountain itself sits on the southwestern rim of the Long Valley Caldera, which was formed by a cataclysmic eruption about 760,000 years ago. A caldera is a cauldron-like depression on the Earth’s surface formed when a magma chamber below the surface is suddenly emptied. The Long Valley Caldera formed when the roof of the magma chamber below it collapsed, ejecting nearly 200 cubic miles (834 cubic kilometers) of material into the air. This is 2000 times larger than the 1980 eruption of Mt. St. Helens. Ash from the Long Valley eruption spread as far east as central Nebraska and Kansas. The surface of the Earth in the area dropped about 2 miles (3 km), and the caldera today is about 18 miles (29 km) east to west, and 10 miles (16 km) north to south. The Long Valley Caldera is one of the largest calderas on Earth.
And if all of this geological activity isn’t enough for you, since 1980 the Long Valley Caldera has begun to rise again, creating a dome in the middle. This is an indication that the magma chamber is refilling below the surface and could again reach a point of eruption. Along with the return of the magma, the region is very geologically active with regular earthquakes, hot springs, and ejection of carbon dioxide from below the surface leaving areas of dead forest.
Today’s photo was taken at Horseshoe Lake in the Mammoth Lakes Basin on the eastern side of the Sierra Nevada mountain range. It was taken with a Canon EF17-40 mm f/4 USM lens set to a focal length of 21 mm on a Canon EOS 5D Mk. III. The exposure was set at 1/15 sec. at f/16 and ISO 100.
Sources:
https://pubs.usgs.gov/dds/dds-81/Intro/facts-sheet/fs108-96.html
http://vesr.nrs.ucsb.edu/valentine/geology
https://volcanoes.usgs.gov/volcanoes/mammoth_mountain/geo_hist_mammoth_lakes.html