Photograph by J.D. Griggs
on
31 January 1984
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). 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.
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.
More about effusive eruptions
Related photo glossary terms:
Did you know?
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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.
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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.