Geography Reference
In-Depth Information
is responsible for volcanoes. But in a relative handful of locales, including Hawaii, the
cause is a “hot spot.” In these instances, hot mantle rock is rising to the base of the litho-
sphere and then rolling back down, like water boiling in a pot. Some of the rock melts as
it rises and the magma rises close to or onto the surface. The latter is the case with the
Hawaiian Islands, and is the very source of their existence.
For the last several millions of years, the Pacific Plate has been moving to the northwest,
passing over a hot spot. Over the eons, magma has come up through a fissure (or vent),
issued onto the ocean floor and hardened, becoming a seamount. As magma continues
to seep through the vent, the seamount grows, breaks the ocean surface, and becomes
an island, which continues to grow as long as the connection with the magma-giving vent
remains. Eventually, however, the moving plate severs that connection and the island
stops growing. A new seamount — the forerunner of a future island — then begins to
grow on the ocean floor. This sequence explains the southeast-to-northwest orientation
of the Hawaiian Islands, as well as why all of the islands except for the Island of Hawaii,
which is now over the hot spot, are volcanically extinct. It also explains why to the south-
east of the Island of Hawaii a seamount exists, which, several thousands (if not millions)
of years from now, will become the next island in the Hawaiian chain.
Nowyoumaysaythatisareally stupidstatement. Whywouldanybodywanteruptionstohap-
pen more often? My point is this: If eruptions happened with greater frequency, then people
would get the message. They would more fully realize the dangers attendant to volcanoes and
be more likely to avoid the danger zones.
But that's not how it works. Eruptions happen infrequently. Subduction is slow, and there's
nothing anyone can do to speed things up. So the people who occupy volcanic environs either
areunaware ofthedangers orlike their chances. Maybe theyevenemploy that popular,cuddly
term “sleeping volcano,” and pray it doesn't wake up in their lifetimes. And indeed, most days
it doesn't. But then one day it does.
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