Kilauea (; Hawaiian: ) is a currently active shield volcano in the Hawaiian Islands, and the most active of the five volcanoes that together form the island of Hawaii. Located along the southern shore of the island, the volcano is between 300,000 and 600,000 years old and emerged above sea level about 100,000 years ago. It is the second youngest product of the Hawaiian hotspot and the current eruptive center of the Hawaiian–Emperor seamount chain. Because it lacks topographic prominence and its activities historically coincided with those of Mauna Loa, Kilauea was once thought to be a satellite of its much larger neighbor. Structurally, Kilauea has a large, fairly recently formed caldera at its summit and two active rift zones, one extending east and the other west, as an active fault of unknown depth moving vertically an average of per year.