The Long Valley Caldera
The Long Valley caldera is about 200 square miles in area and is located south of Mono Lake, California, near the border with Nevada. The biggest explosion was 760,000 years ago, unleashing 2,00 to 3,000 times the amount of ash and lava from the Mount St. Helens explosion. The explosion resulted in the caldera floor dropping a mile. Some of the explosive materials reached as far as Nebraska. The Long Valley caldera has been showing some signs of activity lately. The U.S. Geological Survey recorded strong earthquakes in the area in 1980, along with a 10-inch rise along about 100 square miles of the caldera floor. In the 1990s large amounts of carbon dioxide gas seeped through the ground and killed trees in the Mammoth Mountain, which is part of the caldera. According to volcanologists, these are signs that an explosion might be coming in sometime in the next few centuries.
