The 1868 Hawaii earthquake was the largest recorded in the history of

Hawaii island Hawaii ( ; haw, Hawaii ) is the largest island in the United States, located in the state of Hawaii. It is the southeasternmost of the Hawaiian Islands, a chain of volcanic islands in the North Pacific Ocean. With an area of , it has 63% of t ...

, with an estimated magnitude of 7.9 and a maximum

Mercalli intensity The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

of X (''Extreme''). The earthquake occurred at 4 p.m.

local time Local time is the time observed in a specific locality. There is no canonical definition. Originally it was mean solar time, but since the introduction of time zones it is generally the time as determined by the time zone in effect, with daylight s ...

on April 2, 1868 and caused a

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

and

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

that led to 77 deaths. The

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...

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 The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost Kur ...

formed over the

Hawaii hotspot The Hawaii hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the ...

. Two of the active volcanoes on the Big Island are

Kīlauea Kīlauea ( , ) is an active shield volcano in the Hawaiian Islands. Located along the southeastern shore of the Big Island of Hawaii, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago. Hi ...

and

Mauna Loa Mauna Loa ( or ; Hawaiian: ; en, Long Mountain) is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean. The largest subaerial volcano (as opposed to subaqueous volcanoes) in both mass and ...

with a newer submarine volcano forming the

Kamaʻehuakanaloa Seamount Kamaʻehuakanaloa Seamount (previously known as Lōʻihi) is an active submarine volcano about off the southeast coast of the island of Hawaii. The top of the seamount is about below sea level. This seamount is on the flank of Mauna Loa, the la ...

(formerly Loihi) 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, it has been proposed that the southeastward displacement takes place on a decollement surface near the top of the

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumu ...

. 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

The Hilina Slump is the largest of the active slumps around the Hawaiian islands. The '' 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 Schwartz Lyman (July 25, 1837 – April 14, 1918) was a surveyor, rancher, judge, and politician on Hawaii (island), Hawaii Island. Life Frederick Schwartz Lyman was born July 25, 1837, in Hilo, Hawaii. His middle name is sometimes spe ...

, a goat and sheep rancher at Keaīwa near the epicenter of the events. A sequence of

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) 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 full sequ ...

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

's southwest rift, involved movement of a block that extended seawards for at least . 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 , 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, while thatched houses supported by posts in the same areas were torn to shreds. The earthquake demolished nearly every stone wall and house within the Kaū district in an instant. At Waiōhinu, a large stone church built by Reverend John D. Paris collapsed, and in

Hilo Hilo () is a census-designated place (CDP) and the largest settlement in Hawaii County, Hawaii, Hawaii County, Hawaii, United States, which encompasses the Hawaii (island), Island of Hawaii. The population was 44,186 according to the 2020 United ...

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 coasts caused major destruction at Honuapo, Keauhou (now Keauhou Landing) 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, 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 () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

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

References

{{DEFAULTSORT:Hawaii earthquake, 1868 Hawaii Earthquake, 1868 Earthquakes in Hawaii Geography of Hawaii (island) 1868 tsunamis 1868 in Hawaii April 1868 events Volcanic earthquakes