-
USGS/Cascades Volcano Observatory, Vancouver, Washington
Hot Spots
-
The vast majority of earthquakes and volcanic eruptions occur near plate
boundaries, but there are some exceptions. For
-
example, the Hawaiian Islands,which are entirely of volcanic origin, have
formed in the middle of the Pacific Ocean more than 3,200 km from the nearest
plate boundary. How do the Hawaiian Islands and other volcanoes that form
in the interior of plates fit into the plate-tectonics picture?
-
In 1963, J. Tuzo Wilson came up with the "hot spot" theory. Wilson noted
that in certain locations around the world, such as Hawaii, volcanism has
been active for very long periods of time. This could only happen, he reasoned,
if relatively small, long-lasting, and exceptionally hot regions -- called
hotspots -- existed below the plates that would provide localized sources
of high heat energy (thermal plumes) to sustain volcanism.
-
Specifically, Wilson hypothesized that the distinctive linear shape of
the Hawaiian Island-Emperor Seamounts chain resulted from the Pacific Plate
moving over a deep, stationary hotspot in the mantle, located beneath the
present-day position of the Island of Hawaii. Heat from this hotspot produced
a persistent source of magma by partly melting the overriding Pacific Plate.
The magma, which is lighter than the surrounding solid rock, then rises
through the mantle and crust to erupt onto the seafloor, forming an active
seamount.
-
Over time, countless eruptions cause the seamount to grow until it finally
emerges above sea level to form an island volcano. Wilson suggested that
continuing plate movement eventually carries the island beyond the hotspot,
cutting it off from the magma source, and volcanism ceases. As one island
volcano becomes extinct, another develops over the hotspot, and the cycle
is repeated. This process of volcano growth and death, over many millions
of years, has left a long trail of volcanic islands and seamounts across
the Pacific Ocean floor.
-
Although Hawaii is perhaps the best known hotspot, others are thought to
exist beneath the oceans and continents. Perhaps the best known is the
hotspot presumed to exist under the continental crust in the region of
Yellowstone National Park in northwestern Wyoming.
URL for CVO HomePage is: <http://vulcan.wr.usgs.gov/home.html>
12/21/01, Lyn Topinka