effusive eruption

^{USGS PHOTO GLOSSARY OF VOLCANIC TERMS}

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). Lava flows generated by effusive eruptions vary in shape, thickness, length, and width depending on the type of lava erupted, discharge, slope of the ground over which the lava travels, and duration of eruption.

For example, basalt lava may become `a`a or pahohoe, and flow in deep narrow channels or in thin wide sheets. Andesite lava typically forms thick stubby flows, and dacite lava often forms steep-sided mounds called lava domes.

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Photograph by J.D. Griggs on 31 January 1984

Basalt lava erupts from Pu`u `O`o spatter and cinder cone at Kilauea Volcano, Hawai`i. Lava spilling from the cone has formed a series of `a`a lava channels and flows.

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Did you know?

• 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 km ³ of basaltic lava onto the ground and covered an area of nearly 600 km². About 10,500 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. Between about 17 and 14 million years ago, a series of eruptions with a total volume more than 175 million km³ covered an area of about 165,000 km². Even more voluminous plateau basalts are located in South America, South Africa, and India.