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An Explorit "Science Bytes" article by Kimberly Bernick (2004)

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Hawaii: An Explosive Record of Geological Time

by Kimberly Bernick (2004)

Far out in the middle of the Pacific Ocean, a small island chain has been gradually growing and changing over many, many years. This island chain makes up what we call the Hawaiian Islands. When examining a map of the different islands, it becomes clear that they are organized in a somewhat linear formation, bearing the endpoint islands of Niihua (near Kauai) and Hawaii (the "Big Island"). Is there a reason that these islands exist like this, and if so, what could it be? 

The Birth of an Island 

In fact there is a very simple explanation for the layout of the tropical Hawaiian Islands. One of the large tectonic plates that makes up the Earth's crust, known as the Pacific Plate, covers a great and unbroken expanse beneath the Pacific Ocean. This plate passes over what is known as a "hot spot," a place where molten rock is pushed up through the plate, providing the magma that is necessary for volcanic fuel. It is this magma that, when forced out of those underwater hot spots, can form volcanic islands, such as the Hawaiian Islands. 

The chain formation of the islands is caused from the gradual movement of the Pacific Plate in the northwest direction. As it slowly shifts position, the area that was previously situated over the hot spot moves away from it. Gradually the volcano that was fueled by the hot spot becomes inactive, and the island that was formed from that volcano ceases to grow. 

A Continuous Cycle 

Kauai is one of the oldest of the Hawaiian Islands, and is situated at the northern tip of the island chain. Consequently, it is also one of the most lush and green of the islands. The reason for this is that the volcano that built Kauai moved off the hot spot so long ago that the volcano is no longer active. Since there are no new lava flows growing the size of the island, it gradually succumbs to erosion, weather and aging, and will eventually retreat back beneath the ocean from which it emerged perhaps millions of years ago. 

Looking at a map, one might apply the same logic and say that Hawaii's Big Island must therefore be the newest of the islands. Hawaii is definitely still situated above the hot spot, as is evident from Mt. Kilauea's frequent eruptions, yet soon there may be a newer island emerging from the water southeast of the Big Island. This underwater mountain, Loihi, is quickly growing beneath sea level, and is truly the youngest "unborn" island in the chain. And, as long as the hot spot remains active, there will continue to be new islands added to the line of Hawaii. 

 

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