Plate Tectonics: A whole new way of looking at your planet
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The Book  
Table of Contents
Introduction
In the Beginning
The Tectonic Plates
Mount St. Helen
How Plates Move
Plate Boundaries
A Changing Earth
Pangaea - All Lands
Mid-Ocean Ridges
An Ocean is Born
The Birth of an Island
Mountain Ranges
Subduction Zones
Island Arcs
The Ring of Fire
Faults
Earthquakes
Hot Spots
Mantle Plumes
Origin of Life Theories
Global Climate
Other Worlds
Welcome to Your World

Hot Spots

The Hawaiian islands provide striking evidence of yet another tectonic phenomenon. Stretching to the west and to the north of the big island of Hawaii is a string of smaller islands and submerged volcanoes, or seamounts, 3,700 miles long. Working within the theory of plate tectonics, there is convincing evidence that every one of these islands and seamounts has been formed in the exact place where Hawaii now stands. What is the nature of the forces at work here?

Geologists believe that a huge column of upwelling lava, known as a “plume,” lies at a fixed position under the Pacific Plate. As the ocean floor moves over this “hot spot” at about five inches a year, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate - a veritable conveyor belt of volcanic islands.

Hawaii itself consists of five connected volcanic mountains that were built by this lava plume rising from the mantle. Kilauea, the world’s largest active volcano, is still rumbling because the island has yet to move completely off the hot spot. The farther the other islands in the chain are from Hawaii, the greater their age. About 150 miles to the northwest is Oahu, which burst out of the sea about 3.5 million years ago. Midway, one of the oldest islands in the chain, was formed between 15 and 25 million years ago.

About 2,000 miles from Hawaii, the chain abruptly veers and extends north as a line of submerged volcanoes known as the Emperor Seamounts. This suggests that the Pacific Plate changed course about 40 million years ago. Where the chain’s long march ends the volcanoes are more than 70 million years old. And, not surprisingly, off the southwestern coast of the island of Hawaii, beneath the ocean surface, Loihi, the next Hawaiian Island, is forming as the Pacific Plate continues its journey over this hot spot.

As it stands today, Loihi rises about 6,000 feet above the sea-floor, which brings it very close to the surface. But you won’t be making any immediate vacation plans to the next Hawaiian Island. At its present rate of ascension, scientists predict that Loihi will poke through the surface in about one million years.

Similar trails of conveyor-belt volcaSimilar trails of conveyor-belt volcanoes are found elsewhere in the world, but sometimes a hot spot finds itself under a Mid-Ocean Ridge, a point of sea-floor spreading. When this happens the islands are built on each of the spreading plates, and eventually form a V-shaped pattern as the ocean floors move farther away from the ridge.

The Galapagos Islands off the coast of Ecuador, the Easter Islands, and the Pitcurin Islands in the Pacific are parts of such chains. A number of island chains in the Indian Ocean also appear to have been caused by hot spots beneath mid-ocean ridges. noes are found elsewhere in the world, but sometimes a hot spot finds itself under a Mid-Ocean Ridge, a point of sea-floor spreading. When this happens the islands are built on each of the spreading plates, and eventually form a V-shaped pattern as the ocean floors move farther away from the ridge.

The Galapagos Islands off the coast of Ecuador, the Easter Islands, and the Pitcurin Islands in the Pacific are parts of such chains. A number of island chains in the Indian Ocean also appear to have been caused by hot spots beneath mid-ocean ridges.
   
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