The Hawaiian Islands were formed as the Pacific Plate moved westward over a geologic hot spot. The most populous Hawaiian Island, Oahu, is dominated by two large shield volcanoes that range in age from two to four million years old. However, a fair number of smaller and much younger volcanic craters are also present on Oahu, such as Diamond Head Crater pictured above. Photographer: Charles Carrigan
These younger eruptions were also much smaller in lava output, and much more explosive in nature than the older shield lavas. The younger volcanic craters are all less than 500,000 years old. They formed after Oahu had moved well off the hot spot and the main shield volcanoes had gone dormant for at least two million years. For example, Oahu is now over 200 mi (320 km) from the still-active Kilauea, on the Big Island, consistent with the modern rate of plate motion of four inches (about 10 cm) a year. What caused these younger eruptions of the Honolulu Volcanic Series so long after the island had moved off the hot spot, their precise ages of eruption, and whether they will erupt again, are current points of research and debate among geoscientists. Photo taken on June 12, 2008.