Volcanism: Types of Eruption and the Volcanic Explosivity Index (VEI)
The basic distinction is between explosive und effusive volcanism. Effusive volcanism is characterised by glowing red lava fountains without volcanic ash and by steadily moving lava flows. Volcanoes of this kind have a slight slope, or even consist of just a volcanic fissure. Typically, shield volcanoes occur and lakes of lava can form.
Explosively eruptive volcanoes frequently produce grey eruption clouds that rise high into the sky. The lava of these volcanoes is richer in gas, more viscous and cooler than that of "red volcanism". They have great destructive potential. The classic volcano type of this category is the stratovolcano, which can form beautiful, symmetric cones that can grow several thousand metres high. If lava flows are produced these are usually thicker and cooler. An extreme form of viscous lava flows are lava domes.
The explosive strength of an eruption is registered in the volcanic explosivity index (VEI). This is a logarithmic scale. There are 9 levels (0-8), with an increase of one level corresponding to a multiplication of the explosivity by ten. This does apply to the transition from 0 to 1, which means an increase by the factor 100. To assess the VEI, the height of the eruption cloud is compared with the quantity of tephra emitted. A VEI of 0 corresponds to effusive activity in which only lava flows or lava lakes arise. A VEI 8 describes so-called "supervolcano eruptions" which represent a global catastrophe.
are typical for the volcanoes of Hawaii. The magma contains little gas, has temperatures above 1,000 degrees Celsius and is fluid. Lava fountains are lower than 2 kilometres. These volcanoes also form lava lakes. VEI: 0 - 1
named after the permanently active volcano Stromboli near Sicily. In the very small but regularly occurring explosions, lava fragments can be hurled up to 1 kilometre high into the air. The average height of the eruptions is only a few 100 metres, however. At the same time, lava flows can occur. VEI: 1 - 2
named after the volcano Vulcan, the name giver of all volcanoes. Here there can be stronger explosions, frequently due to phreatic effects. Volcanic ash is thrown up to 15 km up into the air. VEI: 3 - 4
this term refers to activity in which exclusively pyroclastic flows, ash flows and lava avalanches form. They occur either due to dome collapse, the breaking up of an eruption cloud, or by explosions to the side. Volcanic ash is thrown up to 20 km up into the air
the umbrella-shaped eruption cloud up to 60 kilometres. These are the most powerful eruptions of the dangerous volcanoes with acidic, viscous and gas-rich magma. A special danger of Plinian eruptions are pyroclastic flows. They occur when the eruption column collapses. VEI 5 - 8
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