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Seamounts
are individual volcanoes on the ocean floor. They are distinct from the
plate-boundary volcanic system of the mid-ocean ridges, because seamounts
tend to be circular or conical. A circular collapse caldera is often centered
at the summit, evidence of a magma chamber within the volcano. Large seamounts
are often fed by "hot spots" in the deep mantle. These hot spots
are associated with plumes of molten rock rising from the deep within
the Earth's mantle. These hot spot plumes melt through the overlying tectonic
plate and supply magma to seamounts.
Hot spot
plumes are long lived. Therefore, as a moving tectonic plate passes over
a mantle hot spot, a chain of volcanoes is produced with a systematic
age progression - from older to younger. The Hawaiian Islands, the Galapagos
Islands, the Azores, and the Cobb-Eikelberg chain that includes Axial
volcano are all examples of hot spot chains. When a hot spot interacts
with a mid-ocean ridge, the affected ridge segments tend to receive a
greater-than-normal supply of magma from the mantle, leading to more frequent
eruptions, and formation of volcanic edifices right on the ridge. Iceland
and Axial Seamount are both examples of a hot spot located on the axis
of a mid-ocean ridge.
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