Stratovolcano

Composite volcanoes, and stratovolcanoes (from the Latin "stratum " = " layer " ) called, are made ​​up of individual layers of lava and loose masses volcanoes built. They are recognized by their relatively steep, pointed cone shape. Due to the gray, not red hot promotion products they are sometimes referred to as gray volcanoes.

Formation

Cause of their formation is mainly the silica content of the magma, which is at such volcanoes usually between about 55 % and 60 %. This magma is relatively thick - so does not flow very well and forms thick lava flows. These are mostly differentiated magma, so magma that has evolved from basaltic magma or magma that formed by melting of the lower part of the earth's crust. It is relatively cold with about 700 ° C to 900 ° C. The high gas content causes the explosive eruptions run and although usually alternating between emergent loose material, called tephra ( bombs, lapilli, ash ) and lava. Such a sequence causes colds and deposition in the characteristic stratification, which is its name to this volcano type.

The violence of volcanic eruptions, also called Plinian eruptions is, in this form of volcanism so great that the volcanic Locker masses can be ejected as volcanic ash to heights of 40 km in the Earth's atmosphere.

Oust the magma chamber of the volcano then collapses, its summit is replaced by the Caldera said burglary vessel in which forms a new volcanic cone. This form is called Somma volcano. After the classic example of Vesuvius, which consists of the older Monte Somma and the younger actual Vesuvius cone Other examples of Somma - volcanoes are the Pico de Fogo in Cape Verde and the Awatscha on Kamchatka.

The activity of stratovolcanoes is often interrupted by long periods of rest, where the lava solidifies in the volcanic vent. Can the magma ascent when re not penetrate the old chimney, there is a shift of the eruption axis and the new crater formed on the flanks of the old cone. If it remains smaller than the older volcano, it is called adventitious or flank volcano. Two roughly equal stratovolcano cone is referred to as a twin or double volcanoes. This form have, for example, Chimborazo and the Elbrus.

Occurrence

Of the approximately 1,500 active worldwide ( erupted in the last 10,000 years ) volcanoes are about 700 volcanoes layer.

Most composite volcanoes can be found at subduction zones, for example, along the Pacific Ring of Fire, but also to Iceland and the Mediterranean.

Some of her most famous representatives of the Mount Fuji in Japan, Mount St. Helens in the United States, the Pinatubo and Mayon in the Philippines, Vesuvius in Italy, Mount Etna in Sicily, the Lanín in Argentina, the Snæfellsjökul in Iceland and the Merapi on Java.

The highest layer of the earth volcano is Nevado Ojos del Salado in Chile with 6887 m.

The Emperor chair is a low mountain range in Germany, which has its origin in a stratovolcano.