The 1833 Sumatra earthquake occurred on November 25 at about 22:00

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 ...

, with an estimated magnitude in the range of 8.8–9.2 . It caused a large

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 exp ...

that flooded the southwestern coast of the island. There are no reliable records of the loss of life, with the casualties being described only as 'numerous'. The magnitude of this event has been estimated using records of uplift taken from

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...

microatoll A microatoll is a circular colony of coral, dead on the top but living around the perimeter. Growth is mainly lateral, as upward growth is limited by exposure to air. Microatolls may be up to in diameter. They are named for their resemblance to ...

Background

The island of Sumatra lies on the

convergent plate boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

between the

Indo-Australian Plate The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and the surrounding ocean and extends northwest to include the Indian subcontinent and the adjacent waters. It was formed by the fusion of the Indian an ...

and the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent an ...

. The convergence between these plates is highly oblique near Sumatra, with the displacement being accommodated by near pure dip-slip faulting along the subduction zone, known as the

Sunda megathrust The Sunda megathrust is a fault that extends approximately 5,500 km (3300 mi) from Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia. It is a ...

, and near pure

strike-slip faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

along the

Great Sumatran fault The Indonesian island of Sumatra is located in a highly seismic area of the world. In addition to the subduction zone off the west coast of the island, Sumatra also has a large strike-slip fault, the Great Sumatran Fault also known as Semangko ...

. The major slip events on the subduction zone interface are typically of

megathrust Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthqu ...

type. Historically, great or giant megathrust earthquakes have been recorded in

1797 Events January–March * January 3 – The Treaty of Tripoli, a peace treaty between the United States and Ottoman Tripolitania, is signed at Algiers (''see also'' 1796). * January 7 – The parliament of the Cisalpine ...

, 1833,

1861 Statistically, this year is considered the end of the whale oil industry and (in replacement) the beginning of the petroleum oil industry. Events January–March * January 1 ** Benito Juárez captures Mexico City. ** The first stea ...

2004 2004 was designated as an International Year of Rice by the United Nations, and the International Year to Commemorate the Struggle Against Slavery and its Abolition (by UNESCO). Events January * January 3 – Flash Airlines Flight ...

2005 File:2005 Events Collage V2.png, From top left, clockwise: Hurricane Katrina in the Gulf of Mexico; the Funeral of Pope John Paul II is held in Vatican City; " Me at the zoo", the first video ever to be uploaded to YouTube; Eris was discover ...

and

2007 File:2007 Events Collage.png, From top left, clockwise: Steve Jobs unveils Apple Inc., Apple's first iPhone (1st generation), iPhone; TAM Airlines Flight 3054 overruns a runway and crashes into a gas station, killing almost 200 people; Former Pakis ...

, most of them being associated with devastating tsunamis. Smaller (but still large) megathrust events have also occurred in the small gaps between the areas that slip during the larger events, in

1935 Events January * January 7 – Italian premier Benito Mussolini and French Foreign Minister Pierre Laval conclude an agreement, in which each power agrees not to oppose the other's colonial claims. * January 12 – Amelia Earhart ...

1984 Events January * January 1 – The Bornean Sultanate of Brunei gains full independence from the United Kingdom, having become a British protectorate in 1888. * January 7 – Brunei becomes the sixth member of the Association of Southeas ...

2000 File:2000 Events Collage.png, From left, clockwise: Protests against Bush v. Gore after the 2000 United States presidential election; Heads of state meet for the Millennium Summit; The International Space Station in its infant form as seen from S ...

and

2002 File:2002 Events Collage.png, From left, clockwise: The 2002 Winter Olympics are held in Salt Lake City; Queen Elizabeth The Queen Mother and her daughter Princess Margaret, Countess of Snowdon die; East Timor gains East Timor independence, indepe ...

Damage

There is only sparse information available regarding the extent of damage associated with either the earthquake or the subsequent tsunami. However, the tsunami was clearly devastating along the southwest coast of Sumatra from

Pariaman Pariaman ( Jawi: ), is a coastal city in West Sumatra, Indonesia. Pariaman covers an area of , with a coastline. It had a population of 79,043 at the 2010 Census and 94,224 at the 2020 census. "Pariaman" means "safe area". History According to th ...

Bengkulu Bengkulu is a province of Indonesia. It is located on the southwest coast of Sumatra. It was formed on 18 November 1968 by separating out the former Bencoolen Residency area from the province of South Sumatra under Law No. 9 of 1967 and was fi ...

. There is also a lone report of significant damage in the

Seychelles Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...

. The tsunami also caused severe damage in the Maldives and Sri Lanka. Waves have also been reported to reach northern Australia, the Bay of Bengal and Thailand, although in small intensity.

Characteristics

Earthquake

The earthquake shaking lasted 5 minutes in Bengkulu and 3 minutes in Padang, combined with the severity this suggests a very large source rupture. The rupture extent and the magnitude of this earthquake has been determined using the effect of relative sea level changes on coral microatolls from a group of small islands along the outer arc ridge that runs parallel the coast of Sumatra, the

Mentawai islands Mentawai may refer to: * Mentawai Islands * Mentawai Strait * Mentawai people * Mentawai language The Mentawai language is an Austronesian language, spoken by the Mentawai people of the Mentawai Islands, West Sumatra, Indonesia. Dialects Ac ...

. These microatolls, named for their resemblance to island

atoll An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can gro ...

s, can be used to provide a record of sea level change. Microatolls form because the coral head cannot grow up beyond low tide level (known as highest level of survival or HLS) as exposure leads to death. The morphology of the microatolls directly reflects changes in HLS. The presence of annual growth banding combined with the Uranium-thorium dating method allows morphological changes to be dated, with an uncertainty of only a few years to a few decades.

Tsunami

Modelling of the tsunami suggests that most of the energy would have been radiated out into the Indian Ocean, sparing most coastal population centres outside Sumatra itself. Detailed modelling around Sumatra matches well with limited observations available.

References