The formation of the Hawaiian Islands is associated with volcanic activity. At least one volcano formed each island, and as many as five volcanoes formed some of the larger islands.
Hawaii's Big Island has five major volcanoes: Kilauea, Mauna Loa, Mauna Kea, Hualalai and Kohala. Kilauea, Mauna Loa and Loihi (a volcano that is still submerged) are, as of 2014, the currently active volcanoes in the Hawaiian Islands.
The islands formed when the volcanoes erupted with molten basalt, a type of rock. Molten basalt is highly fluid and easily forms lava flows. Basalt eruptions tend to form volcanoes with gently sloping sides. These volcanoes are also called "shield volcanoes."
The volcanoes that formed the Hawaiian Islands came from what volcanologists refer to as the "Hawaiian hot spot." This spot is located under what is now the Big Island of Hawaii. The volcanoes forming the northwest part of the island chain tend to be older, while the volcanoes in the southeast (including those of the Big Island) are younger. Kilauea is the youngest volcano above sea level. Beyond the islands in the northwest, there are submerged former islands called the Emperor seamounts, which are made of even older volcanoes.
While Kilauea, the volcano on the Big Island, has erupted actively since 1983, the volcanoes of the island of Oahu have not erupted for over a million years. Because the volcanoes are part of a single, slowly moving tectonic plate, they may gradually stop erupting as the plate moves away from the hot spot.