Hawaii island is affected by a large number of minor earthquakes related to the movement of magma beneath its active volcanoes. Additionally there are less frequent tectonic earthquakes that are caused either by faulting within the volcanoes or by slip along the basal detachment surface at the top of the oceanic crust associated with the gradual collapse of the island's flanks as it continues to be enlarged. Near Kilauea volcano, the largest structure formed by the collapse of the southeastern flank of the island is the Hilina slump. This slump moves seaward at an average rate of . The slump moved during the May 4 earthquake by about and has moved during previous earthquakes, such as those in 1868 and 1975.