well if you think about it Hawaii was already a volcano that turned into a huge island as the lava froze.
Well, Hawaii has lots of land and ocean, so mountains form, (rocks) and they can erupt easily, they can go in oceans to.
Hawaii's volcanoes are formed due to a hot spot located beneath the Pacific Plate, where magma from the Earth's mantle surfaces to create volcanic activity. As the Pacific Plate moves northwest over the hot spot, it results in a chain of islands that documents its movement over time. The youngest island is currently the Big Island of Hawaii, which is still active with volcanoes like Kilauea and Mauna Loa.
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