The location of earthquakes and how often they occur give vocanologists clues to when and where volcanoes are going to erupt. Also, some tremors are caused by magma. Magma can cause up to 1,000 tremors a day. There are many ways for a volcano to erupt. Eruptions of magma are most common.
Most violent eruptions are steam eruptions, when hot magma reaches the surface water.
Pelean eruptions give off pumice and glowing rocks. In Plinian eruptions there is a violent explosion of gas and thin, fast moving magma. Hawaiian and Strombolian eruptions cause a line of magma fountains. The lava is very fluid. When magma reaches the ocean, pillars of rocks are formed.