Most volcanoes provide various types of warnings before eruptions begin.
Although an explosive eruption could occur without warning, some premonitory events more likely will precede the next eruption. Such an upward movement of magma normally will generate detectable earthquakes, may deform the ground surface, and may cause anomalous heat flow or changes in the temperature and chemistry of the ground and spring waters. People living near volcanoes may detect premonitory events before an eruption. Both the frequency of occurrence and intensity of felt earthquakes commonly increase before eruptions begin. Eruptions may also be preceded by noticeable steaming or fumarolic activity and perhaps by new or enlarged areas of hot ground.