Popular science | Why are there so many types of eruptions in volcanoes?

Volcanic eruptions

Volcanic eruptions have lasted on Earth for many years and have formed unique volcanic "landscapes", such as Mt. Fuji and Achichi, which are world-famous. Today, let's take a look at the various types of volcanic eruptions.

The type of eruption of a volcano depends on the composition of the magma, the volatile content, the temperature and viscosity, the characteristics of the underground magma ascent channel, and the tectonic environment in which the magma erupts. Specifically, such as basalt magma contains low silica composition, contains relatively little volatiles, high temperature, small viscosity, so the magma is fluid, volcanic eruptions are relatively quiet, mostly magma eruptions, can form a large area of lava platforms and shield volcanoes; rhyolite and andesan magma is rich in silica and volatiles, its temperature is low, viscosity is large, poor fluidity, so the volcanic eruption is fierce, the explosion is huge, there are a large number of volcanic ash, volcanic bombs spewed out, often forming a tall volcanic clastic cone, It is accompanied by pyroclastic flows and luminous clouds, often causing severe disasters.

In general, there are several types of volcanic eruptions.

Slit eruptions

Magma overflows the surface through narrow, linear deep faults in the earth's crust, generally without explosion, and the outflow is mainly basalt lava, which condenses to form a lava blanket with a fairly stable thickness and a large coverage area (less volcanic debris).

Many of the fissure eruptions that have occurred throughout history have been in periods of thinner or more active continental barriers. For example, in the Permian period, the Emei basalt erupted in the southwestern yunnan, Guizhou and Sichuan junctions of China, and the current fracture eruption is very common in the mid-ocean ridge (the basalt of the entire ocean crust is formed by multiple eruptions in the mid-ocean ridge rift valley in 200 million years and gradually pushed outward). Iceland, located above the mid-Atlantic ridge, is a visible fissure eruption, hence the name "Icelandic".

Center-type eruption

Magma erupts from the surface along a certain tubular channel, and the lava cover is small, making it the most dominant type of modern volcanic activity. People divide it into tranquil, intermediate and explosive according to the severity of the eruption.

Tranquil eruptions

Also known as the Hawaiian type, it is represented by the Hawaiian volcanoes. When the volcano erupts, only a large amount of hot lava quietly overflows from the crater and flows slowly down the hillside, as if boiling rice soup is boiling out of a rice cooker. The overflow is mainly based on the base molten slurry, which has a high temperature, small viscosity and easy flow. Contains less gas, no explosion phenomenon, and has a certain ornamentality.

Intermediate eruption

It is a transitional type between quiet and violent eruptions, which are dominated by medium-basal lava eruptions. If there is an explosion, the explosive force is not large. It can erupt smoothly for months, or even years, over a long period of time, and is characterized by intermittent eruptions. Represented by the Strambode Volcano, which is close to the Lipari Islands off the west coast of Italy.

Violent eruptions

As the name suggests, when a volcano erupts, a violent explosion is produced, and a large amount of gas and pyroclastic material is spewed out at the same time, and the molten slurry is mainly medium acidic molten slurry.

In summary, the type of volcanic eruption depends on the thickness of the earth's crust, the composition of the magma (such as acidity and matrix, water vapor and volatile content, viscosity, temperature, etc.), the pressure in the underground magma reservoir, the shape of the volcanic channel, and the conditions of seafloor eruptions and continental eruptions. When the magma in the magma chamber gushes out of the surface along a long fault line, it can erupt into a fissure type; if it rises up along the cylindrical channel formed by the intersection of the two sets of faults, a violent central eruption will occur under the action of the pressure inside the magma. Volcanoes are located in different tectonic environments, whether on land or underwater, in ocean ridges or plates, in island arcs or in collision zones, etc., which will cause differences in the types of volcanic eruptions.

Editor/Jing Wang

【Source: Xinhua Net Science】

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