Hot islands
What is the source of the heat and lava on the Big Island of
Hawaii? Why do the islands get flatter as you go northwest? John,
Tijeras, New Mexico
 A
high volcano in Hawaii, getting higher on June 29, 1983.
Individual lava fragments are visible in the spray (ten-stories high) and molten flows are visible
on the flanks of the cone. By September 1986 this cone had spewed out
enough material to become the
highest (820 feet (250 m)) volcanic peak formed on Hawaii in historic times. Photo and text
credit: G.E. Ulrich, Hawaiian Volcano Observatory, U.S. Geological Survey
The heat source
"The lava comes from a plume of molten rock that rises from
deep within the Earth," says Don Swanson, Scientist-in-Charge,
Hawaiian Volcano
Observatory.
The Big Island of Hawaii is centered over this plume, called a hot spot.
"As the Pacific plate moves over the hot spot, magma pushes through the oceanic crust
and, where it reaches the surface, it [piles up and] forms islands," says
Pete Winn,
Colorado geologist.
The Big Island of Hawaii was created this way. The source of the hot spot's heat, however,
is controversial.
"Probably, it is a combination of heat generated by the accretion that formed Earth,
radioactivity within the Earth, self compression of the core of Earth and the dissipation of
earth-tide energy," says Don Swanson.
Flatter islands to the northwest
According to Gary A. Smith, Professor of Geology at the University of New Mexico, the
smaller lower islands of Hawaii began life centered over the hot spot and grew large as the
magma pushed upward. The northwestern drift of the Pacific plate, however, slid the
volcanic centers northwest off the stationary hot spot and they became extinct. The
volcanoes settled to a lower position on the ocean floor as they coasted northwest, down the
bulging hot-spot crust. They became lower still as their weight depressed the ocean crust.
Finally, the volcanoes crumbled under pelting rain delivered by the trade winds.
"Eventually, the islands will subside to near sea level and then be planed off by waves,"
says Smith. |
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