Hawaii sits on the Pacific Plate. Underneath this vast tectonic plate are hot spots, locations beneath the surface of the Earth where magma accumulates. This magma occasionally rises and solidifies on Earth's surface, forming volcanic chains such as the Hawaiian Islands.
The Hawaiian hot spot is estimated to be 200 miles across. The oldest island of Hawaii is Kohala, which is 120,000 years old. The second oldest, Mauna Kea, last erupted around 4,000 years ago. These volcanoes continue to develop as a result of continental drift and seafloor spreading. As each volcano crosses the pacific plate, new volcanoes form directly above the hot spot.