Volcano

Volcanoes occur on the Earth's crust and other planets where magma comes to the surface, releasing various products of volcanism that form hills and mountains.

Terminology

The word "Volcano" comes from the name of the ancient Roman god of fire, Vulcanus (lat. Vulcanus or lat. Volcanus). According to mythology, his workshop was on the island of Vulcano (Italy).

Volcanology is the science that studies volcanoes. Volcanologist - a scientist who studies volcanoes.

Volcanic Activity

The Earth's lithosphere (the planet's rigid outer shell) consists of sixteen larger and several smaller plates. They are in permanent slow motion, due to convection in the underlying ductile mantle. Most of volcanic activity on Earth takes place along plate boundaries, where the lithosphere is being destroyed as the plates are converging or where new lithosphere is being created as are diverging.

Volcanism is most intense in the following geological conditions:

• Divergent plate boundaries, zones of mid-ocean ridges
• Convergent plate boundaries, usually collide of an oceanic plate and a continental plate
• Hot spots in areas of mantle plume uplift
• Continental rifting

Volcanoes on Earth are divided into two types according to their activity:

Active volcanoes (active) - those that have erupted in historical time or during the Holocene (within the last 10,000 years). Some active volcanoes may be considered dormant, but they can still erupt.

Inactive volcanoes (extinct) are ancient volcanoes that have lost their activity.

There are about 900 active volcanoes on land, in the seas and oceans their number is being specified.

The period of a volcanic eruption can last from a few days to several million years.

Shape Classification

The shape of a volcano depends on the composition of the lava it erupts; five types of volcanoes are usually considered:

• Shield-shaped (shield-shaped) volcanoes. Formed by repeated ejections of liquid lava. This form is characteristic of volcanoes that spew low-viscosity basalt lava: it flows for a long time both from the central vent and from the side craters of the volcano. The lava spreads out evenly for many kilometers; gradually these layers form a wide "shield" with flat edges. An example is the Mauna Loa volcano in Hawaii, where the lava flows directly into the ocean; its height from the foot on the ocean floor is about ten kilometers (the underwater base of the volcano is 120 km long and 50 km wide).
• Cinder cones. When such volcanoes erupt, large fragments of porous cinder pile up around the crater in cone-shaped layers, and small fragments form sloping hillsides at the foot; with each eruption the volcano grows higher. This is the most common type of volcano on land. They are no more than a few hundred meters high. Often, cinder cones are formed as side cones of a large volcano, or as separate centers of eruptive activity in fissure eruptions. As an example, several groups of cinder cones appeared during the recent eruptions of Plosky Tolbachik volcano in Kamchatka in 1975-76 and 2012-2013.
• Stratovolcanoes, or "layered volcanoes." Periodically lava (viscous and thick, rapidly solidifying) and pyroclastic substance - a mixture of hot gas, ash and red-hot rocks are erupted. The lava of such volcanoes also flows out of cracks, solidifying on the slopes in the form of ribbed corridors, which serve as a support for the volcano. The examples are Etna, Vesuvius, and Fujiyama.
• Dome volcanoes. Formed when viscous granite magma, rising from the bowels of a volcano, cannot flow down the slopes and solidifies at the top, forming a dome. It clogs up the vent, like a cork that is eventually knocked out by the gases that accumulate under the dome. Such a dome is forming above the crater of St. Helens Volcano, in the northwestern United States, when it erupted in 1980.
• Complex (mixed, compound) volcanoes.

The largest areas of volcanic activity on Earth are South America, Central America, Java, Melanesia, the Japanese islands, the Kuril Islands, Kamchatka, the northwestern United States, Alaska, Hawaii, the Aleutian Islands, Iceland, etc.

Volcanoes exist not only on Earth, but also on other planets and their satellites. Martian volcano Olympus, 21.2 km high is the highest mountain in the solar system.

The Jupiter's moon Io has the greatest volcanic activity in the solar system . Plumes of material erupted by volcanoes on Io reach a height of 330 km and a radius of 700 km (Twashtar volcanoes); lava flows reach a length of 330 km (Amirani and Masubi volcanoes).

On some satellites of planets (Enceladus and Triton) in conditions of low temperatures the erupted "magma" consists not of molten rocks, but of water and light substances. This type of eruption cannot be attributed to normal volcanism, so this phenomenon is called cryovolcanism.