California may be best known for earthquakes, but the state is also home to four active volcanoes. Because an active volcano is classified only as one that has erupted at some point in human history, many people are not aware of these Golden State volcanoes, since most do not represent an imminent threat. Yet it is no coincidence that the state has both volcanoes and earthquakes; seismic activities cause both of these.
The Lassen Peak volcano has had the most recent eruption in California history. In 1915 the volcano spewed hot ashes and gases as far as 200 miles away. The blast caused mudslides and avalanches and destroyed the surrounding area. For the next two years, Lassen Peak continued to erupt on a smaller scale than the initial blast. It is part of the Cascade Volcanic Range, and geologists still closely monitor it. Lassen Peak is in the Lassen Volcanic National Park, where visitors can view boiling mud pits and steam vents caused by the volcano.
Mount Shasta last erupted in the mid-18th century, but debris flows occurred in the 20th century. Due to its elevation, 10,000 feet above the surrounding landscape, Mount Shasta is an impressive formation. The top is a cone, covered with snow year-round. Mount Shasta, also part of the Cascade Range, is located within National Forest land. Visitors to the volcano should take Everett Memorial Highway, which winds past many scenic overlooks and a few campsites. The volcano has no official trails to the summit, though toward the end of the summer, paths begin to appear, having been worn by adventurous hikers.
Long Valley Caldera
Long Valley Caldera has been on the radar of the U.S. Geologic Survey since 1980. The area has shown many signs of impending volcanic activity, including a marked rise in surface elevations, strong emissions of carbon dioxide gas and frequent earthquakes. Long Valley is located on the eastern edge of the Sierra Nevadas, proving that striking natural landscapes are often born out of explosive and dangerous natural processes. Scientists are currently monitoring the caldera closely in order to provide adequate warning to area residents in case of an eruption.
Medicine Lake Volcano
Medicine Lake is called "the sleeping giant" of volcanoes. This shield volcano is 150 miles around and more than 7,900 feet high. Medicine Lake volcano has been erupting on and off for more than 500,000 years, creating formations, such as lava tubes, spatter cones, chimneys and craters. Unlike the forceful explosions of volcanoes such as Mount St. Helens, the Medicine Lake volcano has smaller, gentler lava flows that are far less destructive. The last eruption of Medicine Lake caused the creation of Glass Mountain around the year 1000 A.D. The Medicine Lake volcano is not expected to erupt in the near future.