Volcanoes are elevations that stand separately above canals and cracks in the earth's crust, through which eruption products are brought to the surface from deep magma foci. They have the shape of a cone with a crater on top. The vent of a volcano is a channel that connects the focus to the surface of the earth.
Products that enter the earth's surface differ in volume and composition. In addition, volcanic eruptions can occur with varying intensity and duration. Given these characteristics, the most common classification of activity types has been compiled. It should be noted that one eruption of a volcano can take one or another character.
The Plinian type is named after Pliny the Elder. Roman scientist died during the eruption of Mount Vesuvius in 79 AD e. The Plinian type is particularly intense. The volcanic eruption is accompanied by the release of a large volume of ash to a height of about twenty to fifty kilometers and can last several hours or sometimes even days. Emission products spread over a large area, and their volume is from 0.1 to 50 or more cubic kilometers. The eruption of the volcano according to the Plinian type can result in the collapse of the hill and the formation of the caldera. In some cases, scorching clouds form, but lava flows do not always occur. This type of volcano erupted St. Heles (in the United States) in 1980.
The Pelei type is characterized by the presence of viscous lava. It hardens before exiting, and one or more extrusion domes are formed. So the volcano Montagne-Pele (on the island of Martinique) erupted in 1902.
The volcanic type is characterized by short activity. Eruptions can last several minutes or hours. However, they resume within a few months after a certain number of days or weeks. Eruptions of this type are characterized by the presence of fluid magma, the formation of lava flows. Structures are formed from pyroclastic material and lava. The volume of such stratovolcanoes is from ten to one hundred cubic kilometers. Extrusive domes and ash emissions are not always observed. According to the volcanic type, the volcano Fuego erupts in Guatemala.
The strombolian species is named after the Mediterranean island of Stromboli. This type of eruption is characterized by continuous eruptive activity for several months (sometimes years). Moreover, an eruptive column rarely rises above ten kilometers. Some eruptions form slag cones. They consist of basaltic (predominantly) or andesitic (rarely) slag. Cones, as a rule, are formed during a single eruption, and the volcanoes themselves are called monogenic.
Hawaiian type emissions are characterized by liquid lava output. Fountains from faults and cracks can reach one, sometimes two thousand meters in height. When there is only one vent, the lava diverges radially. In this case, shield elevations are formed with very gentle slopes (up to ten degrees). Such elevations are stacked in layers and do not contain ash. Shield is the largest volcano in the world Manua Loa (in Hawaii). Its height is 4103 meters. This elevation has a length of one hundred and twenty, and a width of fifty kilometers. Streams of its lava spread on the island over an area of more than five thousand square kilometers. Of the forty-two and a half thousand cubic kilometers of volume, more than eighty percent is below sea level.
There are other types of eruptions. However, they are extremely rare. So, for example, as a result of an underwater eruption in 1965, an island was formed in the Icelandic volcano Surtsay.