Effusive and explosive eruptions
Explosive eruptions
When gas and broken fragments of magma are shot up into the atmosphere, this is called an explosive eruption. The broken fragments are called pyroclasts, or if they are smaller than 2 mm we call it volcanic ash.
Effusive eruptions
When lava flows out of a volcano, this is called an effusive eruption.
How do we measure explosive eruptions?
The most commonly used scale to determine the magnitude of an explosive eruption is called the Volcanic Explosivity Index or VEI.It is based on the total volume of erupted material referred to as tephra. The VEI is a discrete scale with numbers going from 0 for non-explosive eruptions up to 8.This means that VEI of 6.5 does not exist. It is either VEI 6 or VEI 7. It is a logarithmic scale, meaning a VEI 7 eruption is 10 times larger than a VEI 6 eruption.In order to determine the VEI of an eruption, volcanologists go out in the field to study the material that has been deposited by ancient eruptions. Through careful mapping, they can determine the extent and thickness of the erupted deposits, which enables them to estimate the VEI.An example of such a map is shown in the figure below.
How do we measure effusive eruptions?
Several effusive eruptions occur every year in locations such as Kilauea volcano in Hawaii, Piton de la fournaise on Reunion Island and Iceland. It is slightly more difficult to measure effusive eruptions.The reason for this is that they tend to have long pauses and the slow outpouring of lava is not continuous in time. So it’s not easy to determine when one ends and a new one begins.The most active effusive volcano in the world today is Kilauea in Hawaii. Its most recent eruption is called the Pu‘u ‘Ō‘ō eruption. It lasted 35 years, starting on the 3 January, 1983. It ended in spectacular fashion in June 2018 with a collapse of the crater floor and the lava lake contained within it.
Over to you
In 2.10 Experiencing volcanic eruptions you chose a volcano and added it to our map. What types of eruption has that volcano experienced? When did they occur?Add and discuss your findings in the comments below.Our purpose is to transform access to education.
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