Before a volcano erupts it gives many warning signs.
Volcanic eruptions are not new to California. According the United States Geological Survey (USGS), California volcanoes will erupt again in the future, causing damage to the health and well-being in the citizens of the state of California as well as to property. While these eruptions cannot be prevented, there are precautions that can be taken to minimize damage and loss of life. Signs of volcanic activity and eruptions in the past abound while signs of potential future eruptions are currently being monitored by the USGS.
California Vents
Over five hundred volcanic vents have been documented in California and up to seventy-six of them have erupted in the past ten thousand years. The volcanic eruptions of the past have ranged from large, catastrophic eruptions to smaller eruptions. The vents that pose the most danger are those that produce great amounts of silicic magma, and several areas in California have the potential to produce such eruptions. These vents produce destructive explosions with the potential to send fiery lava flowing many miles from the source of the eruption. The USGS continues to monitor the activity in these areas for signs of volcanic activity and potential eruptions. The areas include Medicine Lake, Long Valley Caldera, Lassen Peak and Clear Lake.
Unusual Activity
Some common signs of a pending volcanic eruption include swelling and cracking of the ground, small explosions of steam, noticeable changes in hot springs or fumaroles as well as volcanic tremors. Other signs are the formation of new hot springs and fumaroles as well as emission of magmatic gases and unusual melting of snow and ice. The intensity and rate of this activity must be monitored as volcanic unrest is not uncommon and most often doesn't cause eruptions. Since 1980, scientists have been monitoring signs of geologic unrest in the area of Long Valley in California. After a series of earthquakes in that area in 1980 it was noted that the central portion of the Long Valley Caldera was rising. The swelling earth is the result of magma rising beneath the surface of the earth.
Volcanic Tremors and Earthquakes
There are several different types of earthquake that can signal that a volcano is about to erupt. Tectonic-type earthquakes occur as a result of rocks breaking along fractures while volcanic earthquakes are caused by moving magma below a volcano. In comparison, a volcanic tremor lasts longer than a volcanic earthquake and can go on for days. The tremors are caused by the movement of fluids inside the volcano under tremendous pressure. Gases escaping from fumaroles can also cause these tremors, which are signs of volcanic activity and a pending eruption.
Gases
In the early 1990s, carbon dioxide gas seeped up from the magma under Mammoth Mountain in large amounts and killed off trees in a number of areas nearby. The emission of gas from a volcano is one of the signs that the volcano is going to erupt. However, these signs can go on for many years before the eruption occurs. The gases given off by the magma are carbon dioxide and hydrogen sulfide which do not dissolve in water and therefore appear at the surface. An increase in gases like sulfur dioxide and hydrogen chloride at the surface is the sign that the situation is becoming more serious.
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