How did the Hawaiian islands form?
(repsonse geared to a question from a second grader)
The Hawaiian Islands are volcanic in origin. Each island is
made up of at least one primary volcano, although many islands
are composites of more than one. The Big Island, for instance,
is constructed of 5 major volcanoes: Kilauea, Mauna Loa, Mauna Kea,
Hualalai and Kohala. Mauna Loa is the largest active volcano on
Earth. Kilauea is presently one of the most productive volcanoes
on Earth (in terms of how much lava it produces each year).
In general, when you move along the island chain from East to West, the volcanoes become older and older. The two primary volcanoes that make up Oahu (where Honolulu is) have not erupted for well over a million years! The age trend of the volcanoes is thought to be due to the way in which the islands are built on the moving sea floor of the North Pacific Ocean: the Pacific Ocean is mostly floored by a single tectonic plate that is moving over the layer in the Earth known as the Asthenosphere. This movement takes it to the northwest compared to the layers below it at a rate of 5 to 10 cm/yr (the rate depends on where you are on it). As the plate moves over a fixed spot deeper in the Earth where magma (molten lava) forms, a new volcano can punch through this plate and create an island. The Hawaiian Islands are believed to be formed from one such 'hot spot'. As the plate moves away, the volcano stops erupting and a new one is formed in its place. With time, the volcanoes keep drifting westward and getting older relative to the one active volcano that is over the hot spot.
For more information, ask yor public librarian for a copy of "Volcanoes in the Sea: The Geology of Hawaii" by Macdonald, Abbott and Peterson (2nd ed.) Univ. of Hawaii Press, Honolulu (1983).
This book can be purchased at: www.uhpress.hawaii.edu
Dr. Ken Rubin, Associate Professor
Department of Geology and Geophysics
University of Hawaii, Honolulu, HI 96822