The Volcano Explosivity Index
Scientists Use the VEI Scale to Measure the Impact of an Eruption
Jan 2, 2009
Volcanic eruptions can be violent, passive, or anywhere in between. When a people are told that a volcano is going to erupt, many imagine an explosive eruption with a giant ominous cloud of ash and red hot lava flowing down a mountain. However, since volcanic eruptions can vary greatly in size and intensity, volcanologists use the Volcano Explosivity Index, or VEI, to classify the size of an eruption.
The Volcano Explosivity Index
The VEI scale has been used in modern volcanology as a way to forecast the possible size of a volcanic eruption based on that volcano's historical eruptions. It first debuted in 1982 as a paper titled "The Volcanic Explosivity Index (VEI): An Estimate of Explosive Magnitude for Historical Volcanism," written by Christopher Newhall and Steve Self and published in the Journal of Geophysical Research.
The VEI of a volcano depends mostly on the volume of material ejected during the eruption and the height of the ash column or plume. The VEI scale breaks down volcanic eruptions into nine classifications ranging from a VEI of zero to eight - zero being a non-explosive eruption and eight being a mega-colossal eruption. There are no known explosive events with a VEI greater than eight.
Classifying Volcanic Eruptions
Assigning a VEI to a volcanic eruption is standard procedure in modern volcanology. Once a volcano begins to show signs of increased activity, volcanologists assign a VEI based on the characteristics of the current eruption. If the eruption intensifies or weakens, the VEI will be changed accordingly.
An eruption with a VEI 0 is classified as a Hawaiian type of eruption and is described as nonexplosive. These eruptions emit plumes or ash columns less than 100 meters high and eject less than 10,000 cubic meters of volcanic material. These types of eruptions occur daily around the world. A recent example of this type of eruption is the 1984 eruption of Mauna Loa Volcano in Hawaii.
An eruption with a VEI 3 is classified as a Vulcanian to Pelean type eruption and is described as a severe eruption. This type of eruption usually emits plumes and ash columns 3 - 15 km high and ejects more than 10 million cubic meters of volcanic material. These types of eruptions occur about once a year in any given part of the world. The most recent example of a VEI eruption is the 2008 eruption of Chaiten Volcano, Chile.
VEI 6 eruptions are classified as Plinian to Ultra-Plinian type eruptions and are described as colossal. These eruptions usually emit ash and gas columns more than 25 km high (stratospheric eruptions) and eject more than 10 cubic kilometers of volcanic material. These eruption happen infrequently - about once every 100 years. The last eruption of this magnitude was the 1991 eruption of Mt. Pinatubo Volcano in the Philippines. Eruptions of this size can also have impacts on the global climate.
VEI 8 is the largest known eruption size. These eruptions are classified as Ultra-Plinian and are described as mega-colossal. These eruptions are stratospheric and usually emit more than 1,000 cubic kilometers of volcanic material. The last known eruption of this size was Toba Volcano, Indonesia about 73,000 years ago. The amount of material ejected into the atmosphere during this eruption was so great that it is thought to be the main cause of a "volcanic winter" that caused climate change and famine leading to an abrupt decline in the human population about 70,000 years ago.
Currently, the Global Volcanism Program of the Smithsonian Institution utilizes the VEI scale in its daily reports on volcanic activity. Understanding how the VEI scale works helps everyone to visualize just how big, or small, an eruption is. Usually, an eruption of VEI 4 or smaller is not hazardous unless you are near the volcano. Eruptions of VEI 5 or greater can have global and long-lasting impacts.
Source:
Global Volcanism Program, Smithsonian Institution
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