Explosivity
Volcanic eruptions are either effusive or explosive.
Effusive eruptions are 'gentle' eruptions which usually consist of lava out-pours, no pyroclastic material is ejected. These type of eruptions are usually associated with shield volcanoes. On the other hand, explosive eruptions are much more hazardous, where very little lava emerges from the vent and pyroclastic material is predominantly ejected. Explosive eruptions are associated with strato-volcanoes.
The Volcano Explosivity Index, the VEI scale, is a scale used to measure the explosivity of a volcanic eruption. The scale gives an indication of the magnitude of the eruption by taking into account the volume of product released by the volcano, the height of the eruption plume, and how long the eruption occurred for. It is a logarithmic scale, for example, VEI 3 is 10 times more powerful than VEI 2, and 100 times more powerful than VEI 1.
-Lava produced at shield volcanoes is abundant in volcanic gases, however, the magma is of low viscosity due to its low silica content, this allows the gases to escape, meaning that eruptions are usually effusive.
-Lava produced at strato-volcanoes is also abundant in volcanic gases, however the high silica content of the magma results in the gases being trapped in the magma, this leads to more explosive eruptions.
Effusive eruptions are 'gentle' eruptions which usually consist of lava out-pours, no pyroclastic material is ejected. These type of eruptions are usually associated with shield volcanoes. On the other hand, explosive eruptions are much more hazardous, where very little lava emerges from the vent and pyroclastic material is predominantly ejected. Explosive eruptions are associated with strato-volcanoes.
The Volcano Explosivity Index, the VEI scale, is a scale used to measure the explosivity of a volcanic eruption. The scale gives an indication of the magnitude of the eruption by taking into account the volume of product released by the volcano, the height of the eruption plume, and how long the eruption occurred for. It is a logarithmic scale, for example, VEI 3 is 10 times more powerful than VEI 2, and 100 times more powerful than VEI 1.
-Lava produced at shield volcanoes is abundant in volcanic gases, however, the magma is of low viscosity due to its low silica content, this allows the gases to escape, meaning that eruptions are usually effusive.
-Lava produced at strato-volcanoes is also abundant in volcanic gases, however the high silica content of the magma results in the gases being trapped in the magma, this leads to more explosive eruptions.
Below is an example of an effusive eruption:
Below is an example of an explosive eruption: