Top of Page Volcanoes. A volcano explosion is caused by exploding steam and gas, and can be a most fearful natural outburst. Generally, these explosions are caused when fissures are opened by an impending eruption and ground water runs down and contacts the molten lava. The resulting steam can set off powerful explosions. Many eruptions are preceded by numerous earthquakes.
Pressure tends to equalize, and magma follows the path of least resistance.
If successful, it bursts forth as lava. Magma may also contain gas, as well as water or steam, in various quantities. The different content of magma gives volcanoes their individual characteristics. In some cases, lava emerges from a volcano with little fuss and moves slowly over the surrounding country. Sometimes it bursts forth in an explosion, spewing rock, pumice, and ash high into the air.