Active volcanoes are associated with the edges of plates, chiefly with central oceanic ridges and deep sea trenches. u A long the ocean ridges, molten rock material is forced up to the surface between the edges of the separating plates. The magma reaching the surface is called lava . Basaltic lava of volcanoes originates from the asthenosphere. It is cooled rapidly by the sea water, and solidifies.
Volcanic activity of different types. In most volcanoes the magma is forced to the surface. When a volcano begins to erupt, the gases forced out with enormous power throw up lava fragments of various size into the air. In general the dispersion of the debris is followed by the discharge of lava. The dispersed and discharged materials accumulate on each other around the vent. Example: Etna, Vezuv... etc.
Other froms of volcanic activity
Emissions of gases and steam periodically take place from dormant volcanoes. Similar emissions of gases and steam take place in some volcanic regions where active lava eruptions have long since ceased. Superheated water may flow quietly, as in hot springs , or it may be thrown out whit great force and accompanied by steam, as in geysers .
Stromboli is one of the Aeolian Islands of Italy. The island is about 3 miles (2 km) in diameter and 2,900 feet (900 m) above sea level. It rises 10,000 feet (3,000 m) above the floor of the Tyrrhenian Sea. Stromboli is one of the most active volcanoes on Earth. It has been in nearly continuous eruption for about 2,000 years (some volcanologists suggest 5,000 years). Most of the present cone was well developed 15,000 years ago.
Violent eruptions are rare at Stromboli. In 1919, four people were killed and twelve homes destroyed by blocks, some of which weighed 60 tons (50 metric tons). In 1930, during the largest eruption of Stromboli this century, three people were killed by pyroclastic flows. A fourth was scalded to death in the sea near the point the flows entered the ocean. The amount of ash erupted in the explosive eruptions in 1930 was equivalent to that produced during five years of normal, quiet activity.
Mt . Etna Volcano is one of the world's most active volcanoes. It has been erupting for over half a million years. Dormant periods at Mt Etna are extremely rare. Mt. Etna is the largest volcano in Europe and is a real force to be reckoned with. Despite the constant threat to their livelihoods it is also a godsend with what it provides for the residents of the Italian island of Sicily .