1868 Hawaii earthquake
Encyclopedia
The 1868 Hawaii earthquake is the largest recorded in the history of Hawaii island
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...

, causing a landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...

 and tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

 that led to 77 deaths. The earthquake occurred at 4 p.m. local time on April 2, 1868. The aftershock
Aftershock
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...

 sequence for this event has continued up to the present day.

Background

The island of Hawaii (commonly called the "Big Island") is the currently active volcanic center of the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...

 formed over the Hawaii hotspot
Hawaii hotspot
The Hawaii hotspot is the volcanic hotspot that created the Hawaiian Islands in the central Pacific Ocean, and is one of Earth's best-known and most heavily-studied hotspots....

. The two active volcanoes on the Big Island are Kīlauea
Kilauea
Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...

 and Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...

 with a newer submarine volcano forming the Loihi Seamount
Loihi Seamount
Lōihi Seamount is an active undersea volcano located around off the southeast coast of the island of Hawaii about below sea level. It lies on the flank of Mauna Loa, the largest shield volcano on Earth...

 to the southeast of the island. Continued growth of the southeastern part of the island is accompanied by major slumping and southeastward movement of the flanks of the two volcanoes.

This flank displacement is linked to extension within the rift zones associated with both of the active volcanoes, the Mauna Loa and Kīlauea rifts. From the interpretation of seismic reflection data
Reflection seismology
Reflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...

, it has been proposed that the southeastward displacement takes place on a decollement
Decollement
Décollement is a gliding plane between two rock masses. In French, "décoller" means "to detach from" or "to rip off" and was first used by geologists studying the structure of the Swiss Jura Mountains, but is also known as a detachment zone. This is a structure of strata owing to deformation,...

 surface near the top of the oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...

. The slumping is thought to affect only the upper part of the flank as the amount of shortening observed in the toe thrust zone is much larger than that observed in the extensional faults associated with the slumps, but matches well with estimates of extension within the volcanic rift systems.

The Hilina Slump

This is the largest of the active slumps around the Hawaiian islands. The 'backscarp' to the slump is formed by the Hilina extensional fault system, which is known to have moved in both the 1868 event and the 1975 Kalapana earthquake.

Earthquake

A firsthand description of the events was written by Frederick S. Lyman
Frederick S. Lyman
Frederick Schwartz Lyman was a surveyor, rancher, judge, and politician on Hawaii Island.-Life:Frederick Schwartz Lyman was born July 25, 1837, in Hilo, Hawaii. His middle name is sometimes spelled "Swartz"....

, a goat and sheep rancher at Keaīwa near the epicenter of the events.
A sequence of foreshock
Foreshock
A foreshock is an earthquake that occurs before a larger seismic event and is related to it in both time and space. The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the event....

s began on March 27, with tremors every few minutes. They increased steadily in intensity, including one on March 28 that had an estimated magnitude of 7.1. The sequence continued until 4 p.m. on April 2, when the mainshock occurred. One interpretation of this sequence of events is that they were related to the movement of two separate landslide structures on the south side of the island. The first, triggered by an eruption that began in the upper part of Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...

's southwest rift, involved movement of a block that extended seawards for at least 12 miles (19.3 km). The tremors over the next four days are regarded as aftershocks of the 7.1 event caused by this movement. The mainshock involved movement of the entire southern flank of Kīlauea on the basal detachment at an estimated depth of 9 kilometres (5.6 mi), and was probably triggered by the earlier event.

The aftershock sequence has continued for over 140 years until the present day. The aftershock frequency fits a modified Omori (power law) for the first few decades and an exponential function thereafter.

Damage

Wooden houses were knocked off their foundations in Keaīwa, Punaluu Beach and Nīnole
Ninole, Hawaii
Nīnole is the name of two unincorporated communities on the island of Hawaii in Hawaii County, Hawaii, United States. In the Hawaiian language Nīnole means "bending"...

, while thatched houses supported by posts in the same areas were torn to shreds. It demolished nearly every stone wall and house within the Kaū district
Kau, Hawaii
thumb|right|300px|The districts of the [[Hawaii |Big Island]]. From Northernmost, clockwise; [[Kohala, Hawaii|Kohala]], [[Hamakua]], [[Hilo, Hawaii|Hilo]], [[Puna, Hawaii|Puna]], Kau , [[Kona District, Hawaii|Kona]]...

 in an instant. At Waiōhinu a large stone church built by Reverend John D. Paris collapsed, and in Hilo the shaking destroyed the few stone buildings and most walls.

Tsunami

A tsunami was caused by coastal subsidence associated with reactivation of the Hilina slump, triggered by the earthquake. At Kapapala the land subsided by as much as 2 m and formerly dry land was flooded to a depth of 1.5 m.
The tsunami on the Kaū and Puna
Puna, Hawaii
Puna is one of the nine districts in Hawaii County, Big Island, Hawaii. The District of Puna is located on the easternmost portion of the island and shares borders to the north with the District of South Hilo and a border to the west with the District of Kaū...

 coasts caused major destruction at Honuapo, Keauhou and Punaluu. The greatest damage was caused at Keauhou, where a wave height of 12–15 m was reported. All houses and warehouses were destroyed and 46 people were drowned.

Many villages, such as Āpua
Apua, Hawaii
Āpua was an ancient village in the Puna district on the southern coast of the Island of Hawaii in the Hawaiian Islands. A small fishing village was located at about , an elevation about above sea level....

 were never resettled.

Landslides

The earthquake triggered landslides over a wide area.
The largest was a mudslide 3 km wide and 9 m thick, that swept down the flanks of Mauna Loa at Kapapala. It swept away trees, animals and people, causing 31 fatalities.

Effect on volcanic eruptions

Kīlauea was the most affected by the lateral displacement associated with the earthquake, as it did not have another major eruption until 1919. It also disrupted the magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

system beneath Mauna Loa, as is shown both in reduced lava volumes and an abrupt change in the lava chemistry.
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