Eruption on Mount Kanloan causes ashfall events across Negros Island.

Mount Kanlaon, a 2465 m stratovolcano (cone shaped volcano made up of layers of ash and lava) on the northern part of Negros Island in the central Philippines, erupted slightly before 3.40 pm local time on Thursday 19 February 2026, according to the Philippines Volcano Observatories. The eruption comprised a series of explosions which lasted about two minutes and produced an ash column about 2 km high, and followed by a longer period of gas emissions. 

An eruption on Mount Kanloan, Negros Island, the Philippines, on Thursday 18 February 2026. Philippines Volcano Observatories.

The geology of the Philippines is complex, with the majority of the islands located on the east of the Sunda Plate. To the east of this lies the Philippine Sea plate, which is being subducted beneath the Sunda Plate (a breakaway part of the Eurasian Plate); further east, in the Mariana Islands, the Pacific Plate is being subducted beneath the Philippine Sea Plate. This is not a smooth process, and the rocks of the tectonic plates frequently stick together before eventually being broken apart by the rising pressure, leading to Earthquakes in the process. Material from the subducting Philippine Plate is heated by the temperature of the Earth's interior, causing lighter minerals to melt and the resultant magma to rise through the overlying Sunda Plate, fuelling the volcanoes of the Philippines.

Subduction beneath the Philippines. Yves Descatoire/Singapore Earth Observatory.

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At least 116 dead as Typhoon Kalmaegi sweeps across the Philippines.

At least 116 people are now known to have died, with many more still missing, after Typhoon Kalmaegi swept across the central Philippines on Tuesday 4 November 2025. The majority of the deaths occurred in the city of Cebu, and surrounding metropolitan area, with 35 people having apparently drowned in a single incident in the town of Liloan, with 76 people having died in the greater metropolitan area, despite over 400 000 being evacuated from areas deemed to be at risk ahead of the storm. On Mindanao Island a military helicopter taking part in relief efforts crashed during the storm, leading to the deaths of all six crewmembers.

Damage in the city of Talisay on Cebu Island following the passage of Typhoon Kalmaegi on 4 November 2025. Jam Sta Rosa/AFP/Getty Images.

On Negros Island at least 12 people have died and 12 more are still missing after heavy rains triggered a lahar, which buried a number of homes in Canlaon City. Lahars are ash-laden flash floods associated with volcanoes. They can be caused directly by volcanic eruptions, for example when hot lava encounters a glacial lake rapidly destroying an ice dam, but are also common in areas of high seasonal rainfall, where ash deposits from a volcano can build up during the dry season, creating dams on seasonal waterways, which temporarily halt the flow of water, then give way rapidly leading to dramatic flash floods. The Negtos lahar was caused by heavy rains associated with Typhoon Kalmaegi falling onto unconsolidated ash from an eruption on Mount Kanloan last year.

Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area, then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Pacific being referred to as typhoons.

The structure of a tropical cyclone. Wikimedia Commons.

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.

Typhoon Kalmaegi, known as Typhoon Tino in the Philippines, deposited 183 mm of rain onto Cebu Island in the 24 hours before making landfall. When it arrived, it brought with it sustained winds of more than 130 km per hour, with gusts exceeding 180 km per hour. Storms such as this are becoming more frequent due to global warming which is warming the oceans faster than the land, with the Philippines, which typically suffers about 20 storms per year, having been hit by twelve major storms since the typhoon season began in June this year: Tropical Storm Wutip in June, Typhoon Danas, Severe Tropical Storm Wipha, and Severe Tropical Storm Co-May in July, Tropical Depression Fabian and Typhoon Kajiki in August, Tropical Storm Mita, Typhoon Ragasa, and Typhoon Bualoi in September, and Typhoon Matmo, Severe Tropical Storm Fengshen, and Tropical Depression Salome in October. Furthermore, it is thought likely that a system currently known as Tropical Depression Thirty Two, which is currently crossing the central Pacific, will increase in strength and become a Typhoon-strength storm before making landfall in the Philippines this weekend.

A rescue team in the Talamban District of Cebu City following the passage of Typhoon Kalmaegi on 4 November 2025. Philippine Red Cross/Reuters.

As well as leading to larger and more frequent storms, warmer seas can enable them to change course rapidly, making it harder to predict where and when they will make landfall. However, this does not appear to have been the issue in the Philippines this week, where over half a million people were evacuated in advance from areas considered vulnerable to the storm. Instead, the storm has contributed to a growing corruption scandal in the country, with approximately 26.6 billion Philippine Pesos (about US$452 million) having been spent on flood defences which were found to be insufficient, incomplete, or simply absent as the storm approached.

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Eruption and lahar on Mount Kanloan, Negros Island, the Philippines.

Mount Kanlaon, a 2465 m stratovolcano (cone shaped volcano made up of layers of ash and lava) on northern Negros Island in the central Philippines, erupted on Monday 3 June 2024, producing a 5km high column of ash, and subsequent ashfalls in the area around the volcano. On Wednesday 5 June heavy rainfalls in the area produced a series of lahars (mudslides of volcanic ash) which swept down watercourses in some cases entering villages. There are no reports of any casualties, but the Philippine Institute of Volcanology and Seismology has warned that the mud is likely to be toxic, raising concerns about the availability of safe water in the effected villages.

An eruption on Mount Kanloan, Negros Island, the Philippines on Monday 3 June 2024. Dollet Demaflies/AFP/Getty Images.

The geology of the Philippines is complex, with the majority of the islands located on the east of the Sunda Plate. To the east of this lies the Philippine Sea plate, which is being subducted beneath the Sunda Plate (a breakaway part of the Eurasian Plate); further east, in the Mariana Islands, the Pacific Plate is being subducted beneath the Philippine Sea Plate. This is not a smooth process, and the rocks of the tectonic plates frequently stick together before eventually being broken apart by the rising pressure, leading to Earthquakes in the process. Material from the subducting Philippine Plate is heated by the temperature of the Earth's interior, causing lighter minerals to melt and the resultant magma to rise through the overlying Sunda Plate, fuelling the volcanoes of the Philippines.

Subduction beneath the Philippines. Yves Descatoire/Singapore Earth Observatory.

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Eruption on Rincón de la Vieja volcano, Costa Rica.

The Comisión Nacional de Emergencias in Costa Rica has reported a large eruption on Rincón de la Vieja, an active volcano in Guanacaste Province.in the northwest of the country, on Friday 21 April 2023. The volcano produced an ash column about 7.5 km high, and part of the northern perimeter of the volcano's caldera was breached, causing ash-laden waters from the volcano's lake to escape, and triggering a series of lahars along the courses of the Pénjamo, Azúl and Azufrada rivers. This event is not thought to have caused any injuries or damage to infrastructure, but people are being warned to keep away from the affected waterways.

An ash column over the Rincon de La Vieja volcano, Costa Rica, on 21 April 2023. Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional.

Rincón de la Vieja is a complex volcano (volcano with multiple eruptive vents rather than a single crater at the top of a cone-shaped mountain) rising to 1916 m above sea-level in Guanacaste Province in the northwest of Costa Rica. It is located within the Rincón de la Vieja National Park, where along with an associated hot spring system it forms an important part of the local economy. Prior to the onset of activity in September 2014 the volcano had been inactive since September 2011, and the last major eruption occurred in 1966. A small geothermal energy project, the Las Pailas Geothermal Power Plant, runs on heat from underground rocks associated with the volcanic complex.

Rincón de la Vieja forms part of the Cordillera de Guanacaste, a range of volcanic mountains running through northern Costa Rica close to the border with Nicaragua and forming part of the Central American Arc. These volcanoes are fueled by the subduction of the Cocos Plate, which underlies part of the east Pacific Ocean, beneath the Caribbean Plate, on which Central America lies, along the Middle American Trench, which lies off the south coast of the country. As the Cocos Plate is subducted it is gradually melted by the heat and pressure of the Earth's interior, with some more volatile minerals rising through the overlying Caribbean Plate as volcanic magma.

Diagram showing the passage of the Cocos Plate beneath Costa Rica (not to scale). Carleton College.

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Series of eruptions on Mount Popocatépetl.

Mount Popocatépetl, a stratovolcano (cone shaped volcano made up of layers of ash and lava) in the central part of Mexico, has undergone a sharp increase in eruptive activity this week, according to the Centro Nacional de Prevención de Desastres. The volcano erupted 14 times between midnight and 7.15 am local time on Wednesday (2 October 2019), once on Thursday and three times on Friday.  The Centro has issued a warning to the public not to approach the volcano, as there is thought to have been a significant build up of ash on its flanks, which could lead to lahars in the event of heavy rains, which are predicted in the area at this time of year.

An ash cloud over Mount Popocatépetl on 2 October 2019. Hilda Rios/EFE/EPA.

Lahars are ash-laden flash floods associated with volcanoes. They can be caused directly by volcanic eruptions, for example when hot lava encounters a glacial lake rapidly destroying an ice dam, but are also common in areas of high seasonal rainfall, where ash deposits from a volcano can build up during the dry season, creating dams on seasonal waterways, which temporarily halt the flow of water, then give way rapidly leading to dramatic flash floods.

Popocatépetl has been more or less constantly erupting since the mid 1990s, but most of the time this activity remains at a low level. Major eruptions on Popocatépetl are a cause for concern as the volcano is in a densely populated area, with 30 million people living within the potential hazard zone. The last major eruption, a Plinian (or Vesuvian) event in about 800 AD, triggered a series of pyroclastic flows and lahars that scoured the basins around the volcano.

 The location of Popocatépetl. Google Maps.

The volcanoes of the Trans-Mexican Volcanic Belt (including Popocatépetl) are fuelled by the subduction of the Cocos Plate beneath the North American Plate along the Middle American Trench to the south of Mexico. As the subducting plate sinks into the Earth it is melted by the heat and pressure, and volatile minerals liquefy and rise through the overlying North American Plate as magma, fuelling Mexico's volcanoes. 

The subduction of the Cocos Plate beneath the North American Plate in Mexico, and how it leads to volcanoes and Earthquakes. King Saud University.

The Cocos Plate is thought to have formed about 23 million years ago, when the Farallon Plate, an ancient tectonic plate underlying the East Pacific, split in two, forming the Cocos Plate to the north and the Nazca Plate to the south. Then, roughly 10 million years ago, the northwesternmost part of the Cocos Plate split of to form the Rivera Plate, south of Beja California.

 The position of the Cocos, Nazca and Rivera Plates. MCEER/University at Buffalo.

In a paper published in the Journal of Geophysical Research, in 2012, a team led by Igor Stubailo of the Department of Earth and Space Sciences at the University of California Los Angeles, published a model of the subduction zone beneath Mexico using data from seismic monitoring stations belonging to the Mesoamerican Seismic Experiment, the Network of Autonomously Recording Seismographs, the USArray, Mapping the Rivera Subduction Zone and the Mexican Servicio Sismologico Nacional.

 

The seismic monitoring stations were able to monitor not just Earthquakes in Mexico, but also Earthquakes in other parts of the world, monitoring the rate at which compression waves from these quakes moved through the rocks beneath Mexico, and how the structure of the rocks altered the movement of these waves.

 

Based upon the results from these monitoring stations, Stubailo et al. came to the conclusion that the Cocos Plate was split into two beneath Mexico, and that the two plates are subducting at different angles, one steep and one shallow. Since the rate at which a plate melts reflects its depth within the Earth, the steeper angled plate melts much closer to the subduction zone than the shallower angled plate, splitting the Trans-Mexican Volcanic Belt into sections above the different segments of the Cocos Plate, and causing it to apparently curve away from the subduction zone.

 

 Top the new model of the Cocos Plate beneath Mexico, split into two sections (A & B) subducting at differing angles. (C) Represents the Rivera Plate, subducting at a steeper angle than either section of the Cocos Plate. The Split between the two has been named the Orozco Fracture Zone (OFZ) which is shown extended across the Cocos Plate; in theory this might in future split the Cocos Plate into two segments (though not on any human timescale). Bottom Left, the position of the segments on a map of Mexico. Darker area is the Trans-Mexican Volcanic Belt, orange circles are volcanoes, brown triangles are seismic monitoring stations, yellow stars are major cities. Bottom Right, an alternative model showing the subducting plate twisted but not split. This did not fit the data. Stubailo et al. (2012).

  

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

 

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