Tapanuli Orangutans brought closer to extinction by Cyclone Senyar.

The Tapanuli Orangutan, Pongo tapanuliensis, is thought to have moved significantly closer to extinction after Cyclone Senyar passed across Sumatra on 25 November 2025. The species, which was only discovered in 2017, is considered to be the world's rarest Ape, with a population of about 800 all living within an area of less than 1000 km² in North Sumatra. It is considered to be Critically Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species.

A male Tapanuli Orangutan, Pongo tapanuliensis. Maxime Aliaga/Sumatran Orangutan Conservation Program.

Cyclone Senyar caused more than 1000 mm of rain to fall in a day in parts of North Sumatra, triggering a series of catastrophic floods and landslides which killed over a thousand people on the island. The three districts where the species is found, North, Central, and South Tapanuli, have been particularly badly hit, with satellite images showing that between 48 and 72 km² of the forest inhabited by Tapanuli Orangutans has been destroyed, according to Erik Meijaard of Borneo Futures, who has been studying the storm's impact on the Apes. This could potentially equate to between 33 and 55 Orangutans, or between 6.2% and 10.5% of the total population.

So far, only a single dead Orangutan has been found, leading to the possibility that the Apes may have been able to escape the area before the worst of the event, although this is not typical Orangutan behaviour; they usually seek the nearest shelter and attempt to wait out large storms. Even should this have been the case, the storm appears to have destroyed large areas of their native habitat, including food sources, which makes it likely that more Orangutans will be lost in the near future. 

A dead Tapanuli Orangutan found amid storm debris in the village of Pulo Pakkat, North Sumatra, following the passage of Cyclone Senyar. Decky Chandra/The Guardian.

The population was already considered to be threatened by the expansion of mining, hydropower projects and palm oil plantations, within their habitat, as well as a rapidly changing environment, with global warning already having led to an increase in rainfall of between 28 and 160% across Sumatra. One possible benefit to the Orangutans is that the Indonesian government has ordered a halt to all new development projects in the Tapanuli area, pending a survey of the region, which may lead to their gaining some extra long-term protection. The government has also indicated its support for forest restoration projects in the region, which could lead to an increase in the available habitat for the Apes.

The storm is also reported to have completely destroyed the Ketambe Research Station, within the Gunung Leuser National Park in Aceh Province, which was the first specialist Orangutan research centre in the world, opened in 1971 by Dutch primatologist Herman Rijksen, and a leading centre for research into the Sumatran Orangutan, Pongo abelii, which is also considered to be Critically Endangered.

Damage caused to the Ketambe Research Station, within the Gunung Leuser National Park by Cyclone Senyar. American Association of Zookeepers. 

See also...

Over 1000 people thought to have died in Indonesia, Malaysia, and Thailand as a result of Cyclone Senyar.

At least 1000 people are thought to have died, with more than 2700 more known to have been injured and more than 500 still missing after Cyclone Senyar swept across Sumatra and Peninsula Malaysia on 26-28 November 2025. The storm formed as a tropical depression in the Strait of Malacca on 22 November 2025, intensifying to become a tropical cyclone before making landfall on the northern part of Sumatra at about midnight on 26 November 2025. The storm moved southwards along the coast of North Sumatra, before sweeping back across the Strait of Malacca to make landfall on Peninsula Malaysia on 27 November. On 28 November the storm swept out over the South China Sea, where it dissipated several days later without making landfall again.

Flooding in Padangsidimpuan, North Sumatra on 26 November 2025. Badan Nasional Penanggulangan Bencana/Wikimedia Commons.

The passage of Cyclone Senyar resulted in at least 753 deaths on Sumatra, with a further 2600 injured and 526 people still missing, largely as a result of flooding and landslides. Over 1.2 million people on the island have been displaced because of the storm with about 3.3 million affected in some way, across the provinces of North Sumatra, West Sumatra, and Aceh. The storm is reported to have destroyed 3600 homes, and damaged a further 5800, along with 344 bridges and 324 schools.

A woman clearing mud from a house in the town of Meureudu in Aceh Province, Sumatra, following the passage of Cyclone Senyer. Hotli Simanjuntak/EPA.

The storm caused less damage in Peninsula Malaysia, where people had more time to prepare, with three fatalities, and 34 000 people evacuated from high-risk areas ahead of the storm. However, in neighbouring part of southern Thailand, flooding associated with the storm killed at least 267 people, with most of the fatalities occurring in Songkhla Province, according to government figures; although some sources have accused the government of downplaying the size of the disaster, with suggestions that more than 1000 people may have died in Songkhla Province alone. In addition, at least 102 people were injured, with two homes destroyed and 1074 damaged, along with 228 roads, 12 bridges, 41 schools and 38 temples. The city of Hat Yai in Sonhkla Province received 372 mm of rain on 21 November, more than is typical for the entire month of November, and more rain than has fallen on the city in a single day in 300 years of records.

Flooding in Songkhla Province, southern Thailand, on 26 November 2025. AP.

Tropical storms, called Cyclones in the Indian Ocean and South Pacific, are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

The formation of a tropical cyclone. Natural Disaster Management.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms. 

The formation and impact of a storm surge. eSchoolToday.

However, Cyclone Senyar is unusual in that it formed in a part of the world not usually prone to tropical storms; it is only the first such storm ever to form in the Strait of Malacca, and the second to cross these waters, after Typhoon Vamei, which formed in the South China Sea in 2001, and crossed Peninsula Malaysia from east to west. This is because the Strait of Malacca is close to the equator, an area where it was once thought that tropical storms could not form, as the Coriolis Force is not strong enough. However, warming global sea temperatures appear to be making this possible, as more heat is effectively more energy, and this is the fifth such near-equator storm of 2025. This means that communities in these areas are not as used to tropical storms as communities in areas where they are a long-standing problem, and infrastructure has not typically been built with large storms in mind, greatly increasing the damage and casualties caused when they appear.

See also...

Eruption on Mount Sinabung produces 5 km high ash column and leads to ash falls 20 km from its summit.

Mount Sinabung, a 2460 m stratovolcano (cone shaped volcano made up of layers of ash and lava) in North Sumatra, Indonesia, erupted on Monday 10 August 2020, producing an ash column that rose 5 km into the atmosphere, and producing ash falls up to 5 km deep in (previously evacuated) villages up to 20 km from the summit of the volcano. Nobody was injured in this incident, largely due o an existing evacuation order that prevents people from approaching the volcano, with nobidy allowed to approach within 5 km of the volcano, and villages evacuated over a wider zone. 

An ash column over Mount Sinabung, North Sumatra, on Monday 10 August 2020. Sugeng Nuryono/AP

Sinabung is considered to be a potentially very dangerous volcano, as a large number of people live in its immediate vicinity. The last major eruption prior to the twenty-first century happened in about 1600, with small eruptions occurring in 1889 and 1912. However the volcano returned to life in late August 2010, erupting throughout September and causing about 12 000 people to flee their homes, and has been erupting intermittently ever since.

 

The location of Mount Sinabung. Google Maps.

 

The Indo-Australian Plate, which underlies the Indian Ocean to the west of Sumatra, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Sumatra and neighbouring Java, along the Sunda Trench, passing under Sumatra, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fuelling the volcanoes of Sumatra.

 

The Subduction zone beneath Sumatra. NASA/Earth Observatory.

 

The two plates are not directly impacting one-another, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.

 

The movement of the tectonic plates around Sumatra. NASA/Earth Observatory.

 

See also...

 

 

 

 

 

 

 

 

 

 

Follow Sciency Thoughts on Facebook.