Beyond Kure the tops of the seamounts get progressively lower. The geological characteristics of the underwater part of Necker Island indicate that it once was more than 1,000 meters (3,000 feet high), but today the highest point on the island is less than 100 meters (300 feet) above sea level.
An example is Necker Island, which is about 300 miles northwest of Kauai and is twice as old, at about 10 million years. The older islands beyond Kauai have much lower elevations. The highest peak on the Big Island is almost 4,250 meters (14,000 feet), while the island of Kauai rises to only about 1,500 meters (5,000 feet). Thus, in Hawaii, the newest islands should be the tallest ones-which again is just what is found (see Figure 6). As volcanic islands age, they gradually subside and erode. In fact, by comparing the ages of the volcanoes with their separations, geologists have concluded that the crust of the Pacific Ocean is moving at a rate of about 10 centimeters (4 inches) per year over the hot spot, or about one meter per decade.Īnother source of supporting evidence involved the elevations of the islands and seamounts. This pattern is exactly what had been predicted by the hypothesis that the volcanoes were created by the movement of the crust over a source of heat. To the northwest, the volcanoes are progressively older, with Suiko Seamount in the northern part of the chain having an age of 65 million years. The islands of Oahu and Kauai have greater ages, with the latter being about five million years old. The islands of Maui, Molokai, Lanai, and Kahoolawe, which once were joined in a landmass known as Maui Nui, are the next older. These measurements showed that the Big Island of Hawaii, at the southeastern end of the archipelago, is the youngest of the chain, with an estimated age of less than half a million years ( Panel 1). The higher the ratio, the older the rock. To determine the age of a volcanic rock, scientists can measure the amount of argon and the amount of radioactive potassium in the rock. This potassium decays at a known and constant rate into argon, and the argon remains trapped in the rock. But volcanic rocks also contain a radioactive form of the common element potassium. Immediately after lava cools, it contains no argon because the gas is expelled from the molten rock. Geologists can measure the age of volcanic rocks by measuring the quantities of argon gas in those rocks. For example, the hypothesis predicts that the more northwesterly seamounts and islands should be older than the islands to the southeast. Once this hypothesis was proposed, scientists began searching for evidence to test it. The present island of Kauai formed about 5 million years ago Maui Nui, the landmass now represented by Maui and nearby (more.)
The Hawaiian islands formed as the Pacific Ocean floor moved over an underlying hot spot in the earth, shown here by a dotted circle. As the islands continued to move toward the northwest, away from the hot spot, they were eroded by the wind, rain, and waves and eventually sank below sea level to become seamounts. Meanwhile, a new island was forming so that over time a chain of islands was produced extending away from the hot spot. As the oceanic crust moved over the hot spot, each recently formed volcano was carried away from the hot spot toward the northwest, cutting off its source of lava. Eventually these erupting volcanoes grew large enough to rise above sea level and form islands (see Figure 5). This hot spot, as it came to be known, produced lava that erupted through the crust onto the ocean floor. He suggested that the islands formed as the crust of the Pacific Ocean floor moved over a source of heat positioned beneath the crust (see Figure 4). Tuzo Wilson proposed a hypothesis to explain the archipelago's origins. The islands currently above water are shown in solid black, with the populated chain of major islands located (more.)
#MAUI REVEALED EBOOK SERIES#
The Hawaiian-Emperor volcanic chain stretches from the Big Island of Hawaii to Kure Atoll and then continues underwater as a series of seamounts.
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