Unfortunately volcanic eruptions cannot be prevented. However, as a volcano becomes active, it gives off a number of warning signs. These warning signs are picked up by volcanologists, the volcano is monitored, and recommended actions are given to people in the immediate area.
Volcanic eruptions are most likely to occur in the Pacific Rim states and the danger area around a volcano covers approximately a 20-mile radius, although there is some danger to people within 100 miles or more. Airborne ash from a volcano can affect people hundreds of miles away from the eruption.
The USGS Volcano Hazards Program issues four-tiered Volcano Alert Levels of Normal, Advisory, Watch, and Warning. The Volcano Alert Levels are intended to inform people on the ground about a volcano's status and are issued in conjunction with the Aviation Color Code. Notifications are issued for both increasing and decreasing volcanic activity.
Volcanic eruptions often force people living near volcanoes to abandon their land and homes. Those living farther away are likely to avoid complete destruction, but associated hazards such as gases, lahars, landslides, flooding, lava flows, pyroclastic flows, tephra, and ash can still be damaging.
A volcano is a mountain that opens downward to a reservoir of molten rock below the surface of the earth. Unlike most mountains, which are pushed up from below, volcanoes are vents through which molten rock escapes to the earth’s surface. When pressure from gases within the molten rock becomes too great, an eruption occurs.