Photoglossary

Effusive eruption

An eruption dominated by the outpouring of lava onto the ground is often referred to as an effusive eruption (as opposed to the violent fragmentation of magma by explosive eruptions).

Facts and Figures: The world's largest historical effusive eruption occurred in 1783 from the 25-kilometer-long Laki Fissure in southern Iceland. The 8-month long eruption poured about 15 cubic kilometers of basaltic lava onto the ground and covered an area of nearly 600 square kilometers. About 10'000 people, one-fifth of Iceland's population, and thousands of sheep, horses and cattle died as a result of the eruption, primarily from starvation.

The largest known effusive eruptions on Earth have paved hundreds to thousands of square kilometers of its surface with basaltic lava. Erupting hundreds of lava flows over a period of a few million years, scientists refer to the resulting deposits as flood basalt and the areas covered as plateau basalt. One such area covered with flood basalt is the Columbia Plateau region of eastern Washington and Oregon, USA. Between about 17 and 14 million years ago, a series of eruptions with a total volume more than 175 million cubic kilometers covered an area of about 165'000 square kilometers. Even more voluminous plateau basalts are located in South America, South Africa, and India.

Eruptions of Kilauea volcano, Hawaii, are mainly effusive. Pahoehoe lava flow July 1991. Photo: J. Alean

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