Hawaii hotspot
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The Hawaii hotspot is perhaps the best known volcanic hotspot on Earth,[1] responsible for the Hawaiian Islands in the Pacific Ocean.
Almost all magma created by the hotspot is basalt; the Hawaiian volcanoes are constructed almost entirely of this igneous rock or the similar coarse-grained gabbro and diabase. Rarely, there are igneous rocks with compositions unlike basalt, such as nephelinite. Most eruptions are Hawaiian eruptions because basaltic magma is fluid compared with magmas typical in more explosive eruptions such as the andesitic magmas producing spectacular and dangerous eruptions around Pacific Basin margins.
Over 70 million years, Hawaii hotspot eruptions have left a trail of underwater mountains across the Pacific, called the Hawaiian-Emperor seamount chain. This is a vast underwater mountain region of islands, seamounts, atolls, shallows, banks and reefs, southeast to northwest beneath the northern Pacific. A sharp bend in the chain at 43 Ma is explained by a change in the Pacific Plate motion. The oldest volcano in the chain is Meiji Seamount at 82 million years, and the youngest Loihi Seamount.[2]
Hawaii is the largest and youngest island in the chain, built from five volcanoes. Mauna Loa, comprising over half of the Big Island, is the largest shield volcano on the planet. From sea level to summit, it is over 4km, from sea level to sea floor, 5km. (USGS)
1.2 million years ago, the Hawaii hotspot created an island 50% larger than present day Hawaii called Maui Nui, built from seven shield volcanoes. 200,000 years ago it subsided, forming islands Maui, Molokai, Lanai and Kahoolawe. The most recent volcanic activity at Maui Nui was about 1790 at Haleakalā. Haleakalā has been active in the last 30,000 years, producing numerous small lava flows.
