Has Hawaii come from an underground volcano? How long can a volcano erupt for?
Topaz Class from Oxfordshire (Aged 5-14)
Filed under: age 5-14, Answered Big Questions, Environment & Natural World Big Qs, Geology Big Questions, Steve Drury's Big Answers
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Yes it has, but it is more interesting than that. The ‘Big Island’ of Hawaii has huge active volcanoes and sits on top of a hot spot in the Earth that is a long way below the surface. If you look at rocks that make up the Hawaiian islands that are to the west you find that they are solidified lavas, but there are no active volcanoes today. The lavas can be dated, and going westward along the Hawaiian island chain (look at an atlas) they get older and older.
For this to have happened the upper part of the solid Earth (the crust ) must be moving slowly westwards, while the deeper part (the mantle) stays still. The hot spot source of the lavas that feed the volanoes on the Big Island is fixed in the mantle. As crust moves over the hot spot lavas build up on top of the crust until they form a volcano that breaks through the ocean surface – that is what’s happening at the Big Island now. But the movement of the crust slowly drags the island away from the hot spot, cutting off the lava supply and the island’s volcanoes become extinct. In the Hawaiian chain this has been going on for millions of years, so as well as the once volcanic islands stretching out to the west, there are drowned volcanoes in a line that extends even further west.
If you dragged a piece of paper over a candle flame, you would get a very similar effect – a line of burn marks showing the path taken by the sheet of paper. The Hawaiian chain is one of the best pieces of evidence that shows that the outer Earth is continually moving relative to the deeper Earth underneath.