The Big Island is formed of five coalesced volcanoes of successively younger ages, the older ones apparently extinct .
Shield volcanoes have summit calderas formed by piston-like subsidence.
Many smaller pit craters also occur along fissure zones on the flanks of the volcanoes. These form by collapse due to withdrawal of magma along conduits. View from Pohue Bay, south coast of Hawaii, northward toward Mauna Loa volcano. The broad curving horizon line is the summit of Mauna Loa which stands over 14,000 feet above sea level and 30,000 feet above the sea floor. It is the highest mountain on Earth.