page_title: Hilina Slump
section_title: Geology
hierarchical_section_title: Hilina Slump / Geology
caption_attribution_description: English: The Hilina Pali on Kīlauea Volcano's south flank is visible evidence of the steep Hilina Fault System. Beneath this system lies the flat-lying detachment fault that has no visible surface expression, but has produced several large earthquakes in the past 200 years.
context_page_description: The Hilina Slump, on the south flank of the Kīlauea Volcano on the southeast coast of the Big Island of Hawaiʻi, is the most notable of several landslides that ring each of the Hawaiian Islands. These landslides are the means by which material deposited at a volcano's vents are transferred downward and seaward, eventually spilling onto the seabed to broaden the island.
  Kīlauea's entire south flank, extending out to Cape Kumukahi, is currently sliding seaward, with some parts of the central portion moving as much as 10 centimeters per year, pushed by the forceful injection of magma and pulled by gravity.
  Current movement of the Hilina slump and recent volcanic activity, coupled with evidence of massive submarine slides in the geological past, has led to sensationalistic claims of megatsunamis that might result if the south flank of Kīlauea should suddenly fail. Geologists are confident no such failure is likely, and other experts have stated that the supposed threats of megatsunamis are exaggerated.
context_section_description: The Hawaiian Islands are volcanoes, the newest part of the Hawaiian-Emperor seamount chain, created by eruption of magma from the Hawaiʻi hotspot. As the Pacific plate, moving to the northwest, carries the existing volcanoes away from the hotspot, new volcanoes form at the southeastern end. The newest and largest island is the Big Island of Hawaiʻi, formed by the merger of seven volcanoes. The largest, at the trailing edge of the island, is Mauna Loa Volcano, and on its seaward flank is the younger Kīlauea, with the still submerged Lōʻihi Seamount just off-shore.
  The Hawaiian volcanoes are shield volcanoes, distinguished from the more familiar stratovolcanoes by their greater breadth and lower gradient slopes. (E.g.: Kilauea's average slope to the east is only 3.3°, and the south slope from the summit to the ocean floor averages only 6°.) When the volcano is over the hotspot a plentiful supply of magma allows it to build a broad shield; when it loses its supply of magma it dies and is eroded back to sea level.
  Like the rest, Kīlauea is composed of alternating subaerial and submarine lava flows fractured by cooling joints and interbedded with weaker rock, sediments, and tephra, resulting in what has been characterized as a fractured rock mass. These discontinuities form zones of weakness that lead to slope failure. The weight of the rock mass causes extension (stretching) downhill, favoring the formation of vertical structures, such as dip-slip faults and rift zones, parallel to the slope. These disconnect the rock mass from the upper flank, putting more stress on any non-vertical planes of weakness, which may fail and form a slip zone.
  On Kīlauea's seaward flank (where it is not resting against Mauna Loa) these tendencies are evident where magma oozing out of the caldera turns east and west to form the Southwest Rift Zone (SWRZ) and East Rift Zone (ERZ), both parallel to the shore, and also in the cliffs of the Hilina Pali – coincident with dip-slip faults of the Hilina fault system – which form the head-scarp where a large block of rock has slumped down and outward.
  The rift zones enable transport of lava tens of kilometers away from the caldera (as seen in the current lower Puna eruption). They also serve as wedges, forcing the south flank of Kīlauea downslope across a décollement – a nearly horizontal fault where the volcanic deposits rest on the oceanic crust – about 8 to 10 km deep. The combination of rifting and gravitationally driven slumping results in seaward movement of the entire south flank (see image), especially around the Hilina Pali, with seaward motions of up to 10 centimeters (~4 inches) per year.
caption: The Hilina Pali (cliff) on Kīlauea Volcano's south flank is visible evidence of the steep Hilina Fault System. Beneath this system lies the flat-lying detachment fault that has no visible surface expression, but has produced several large earthquakes in the past 200 years.
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