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  • Reports of landslides triggered by the 8 June 2026 M=7.8 earthquake offshore Mindanao in the Philippines Dave Petley
    To date news reports suggest two fatal landslides with a combined toll of 17 people. There are various news reports trickling in about the landslides triggered by the 8 June 2026 M=7.8 earthquake offshore Mindanao in the Philippines. As usual, the remote locations of many of the landslides means that the information is a bit hit and miss at this point. To date, the most serious event appears to have occurred at a community called New Aklan, located in Glan, Sarangani. It appears that
     

Reports of landslides triggered by the 8 June 2026 M=7.8 earthquake offshore Mindanao in the Philippines

9 June 2026 at 07:31
A failure in a coastal cliff at Sitio Buhangin, Barangay Patuco, Sarangani following the 8 June 2026 earthquake near Mindanao.

To date news reports suggest two fatal landslides with a combined toll of 17 people.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

There are various news reports trickling in about the landslides triggered by the 8 June 2026 M=7.8 earthquake offshore Mindanao in the Philippines. As usual, the remote locations of many of the landslides means that the information is a bit hit and miss at this point.

To date, the most serious event appears to have occurred at a community called New Aklan, located in Glan, Sarangani. It appears that New Aklan is at: [5.7705 N, 125.3356]. News reports indicate that 13 people were killed, although there are also indications of additional fatalities in this area.

A further four people are missing under a landslide at Sitio Buhangin, Barangay Patuco, Sarangani. Patuco is in the area of [5.4770, 125.4859]. This appears to have been a failure on a coastal cliff:-

A failure in a coastal cliff at Sitio Buhangin, Barangay Patuco, Sarangani following the 8 June 2026 earthquake near Mindanao.
A failure in a coastal cliff at Sitio Buhangin, Barangay Patuco, Sarangani following the 8 June 2026 earthquake near Mindanao. Image tweeted by Radyo Pilipinas.

Over the next few days, satellite imagery should become available that will help identify the landslide impacts, but in the meantime Dan Shugar has identified some (using Planet imagery, I’d imagine):-

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  • Fatalities from landslides in earthquakes Dave Petley
    A new study (Sun et al. 2026) shows that in six earthquakes in China between 2010 and 2022, landslides and rockfalls were responsible for at least half of the total fatalities. It is well-established that landslides are a major cause of loss of life in earthquakes in mountainous areas. The seismology maxim that “it is not earthquakes that kill people, it’s collapsing buildings” does not apply in its pure form in mountains – landslides also kill large numbers of people. An earthquake
     

Fatalities from landslides in earthquakes

27 May 2026 at 08:41
An earthquake triggered landslide from the 2008 Wenchuan earthquake.

A new study (Sun et al. 2026) shows that in six earthquakes in China between 2010 and 2022, landslides and rockfalls were responsible for at least half of the total fatalities.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

It is well-established that landslides are a major cause of loss of life in earthquakes in mountainous areas. The seismology maxim that “it is not earthquakes that kill people, it’s collapsing buildings” does not apply in its pure form in mountains – landslides also kill large numbers of people.

An earthquake triggered landslide from the 2008 Wenchuan earthquake.
An earthquake triggered landslide from the 2008 Wenchuan earthquake.

However, the actual number of people killed by landslides in earthquakes is poorly understood. This is largely due to the challenges of collecting reliable information in the aftermath of a major earthquake, when the focus is on rescue and recovery rather than data collection. For this reason, many studies of landslide fatalities do not include seismically-triggered events. This is true of my own work.

However, a study has just been published (Sun et al. 2026) in the journal Natural Hazards Review that starts to address this issue. The paper nominally examines fatalities from all causes from earthquakes in China from 2001 to 2022. However, the authors note that the data has low reliability until 2010, so I’ll focus on the period from 2010 to 2022. I also note that the authors use the term “geological hazards“, which is a little broader than landslides. I should note that the paper isa broad look at fatalities from earthquakes – there is a much richer range of analyses than I will cover here.

In the period from 2010 to 2022, Sun et al. (2026) identified 14 earthquakes in which geological hazards caused loss of life. In some cases, the impacts were substantial. Thus, the M=6.5 3 August 2014 earthquake at Ludian in Yunnan led to 134 fatalities and 40 people missing from geological hazards from a total of 728 fatalities (c.24 % of the total), whilst the 5 September 2022 M=6.8 earthquake at Luding in Sichuan led to 76 geological hazard fatalities and 25 missing from a total of 118 fatalities (c.86% of the total). In six of the 14 examples, geological hazards caused at least 50% of the fatalities.

Sun et al. (2026) highlight that “fatalities from geological hazards concentrate in geologically complex, mountainous provinces, i.e., Sichuan, Yunnan, Gansu, Guangxi, and Guizhou”. They note that even small events can trigger fatal landslides – for example, six people were killed in a rockfall triggered by a M=4.3 earthquake in Guizhou in 2010, whilst a M=2.8 aftershock from the Yanjin earthquake in 2006 triggered a rockfall that killed a person.

This is an incredibly useful study. It starts to shed light on the impact of landslides in large earthquakes. It is not the definitive study, and questions remain – not least, the pattern of landslide losses in very large earthquakes, like the 2010 Wenchuan event, in which landslides were ferocious. But it forms the basis for such investigations, starting to fill a major gaps in our understanding.

Reference

Sun, B. et al. 2026. Causes Analysis of Earthquake-Related Deaths in Mainland China 2001–2022. Natural Hazards Review, 27 [2]. https://doi-org.ntu.idm.oclc.org/10.1061/NHREFO.NHENG-2458

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  • On the growth of research in landslides Dave Petley
    Since 1994 there has been a 32 times increase in the number of research outputs with the keyword “landslide”. In a couple of weeks time, I have the pleasure of being one of the invited speakers at the Landslide Risk and Geoengineering (LaRGE) Conference in Queenstown, New Zealand. Ahead of that presentation, I’ve been using Scopus to look at the growth of research in landslides since 1994, the year that I submitted my PhD thesis. This graph, from Scopus, shows the number of research
     

On the growth of research in landslides

16 April 2026 at 06:57
The number of outputs using the keyword "landslide" in the period 1994 to 2025 inclusive, via Scopus.

Since 1994 there has been a 32 times increase in the number of research outputs with the keyword “landslide”.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

In a couple of weeks time, I have the pleasure of being one of the invited speakers at the Landslide Risk and Geoengineering (LaRGE) Conference in Queenstown, New Zealand. Ahead of that presentation, I’ve been using Scopus to look at the growth of research in landslides since 1994, the year that I submitted my PhD thesis.

This graph, from Scopus, shows the number of research outputs per year that use the keyword “landslide”. It is simple and unfiltered:-

The number of outputs using the keyword "landslide" in the period 1994 to 2025 inclusive, via Scopus.
The number of outputs using the keyword “landslide” in the period 1994 to 2025 inclusive, via Scopus.

The extraordinary growth in productivity is clear – to put it into context, in 1994 the number of outputs was 182; in 2025, it was 5,875, a 32x increase. This is a remarkable improvement in the volume of our understanding of landslides, although it does not say anything about paradigm change.

It is interesting to look at some of the key publications for landslide research:-

The number of outputs using the keyword "landslide" for selected key publications in the period 1994 to 2025 inclusive, via Scopus.
The number of outputs using the keyword “landslide” for selected key publications in the period 1994 to 2025 inclusive, via Scopus.

The journal Landslides started in 2004 and has shown remarkable growth (although note it still represents a tiny proportion of the total outputs per year). There are also large increases in the journals Natural Hazards and Engineering Geology, and a smaller increase for journal Geomorphology. On the other hand, those journals that traditionally would have been associated with landslide research, such as QJEGH, Canadian Geotechnical Journal and Geotechnique, have remained essentially static over time.

I suspect that this represents a growth in the academic areas researching landslides, and in particular a diversification from geotechnical engineering to a much more broader range of research that encompasses people with an interest in geomorphology, remote sensing, geophysics and natural hazards.

There is one other element that is important here too, which is the growth of landslide research in China. This graph shows the same data as above but with China as the national affiliation of one or more author:-

The number of outputs using the keyword "landslide" and with an affiliation from China in the period 1994 to 2025 inclusive, via Scopus.
The number of outputs using the keyword “landslide” and with an affiliation from China in the period 1994 to 2025 inclusive, via Scopus.

The growth in landslide research productivity in China is explosive over the last ten years, and with 2,616 outputs in 2025, Chinese affiliated authors are now producing over 55% of the world’s landslide research. There is no doubt as to where the centre of gravity now lies in landslide science.

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  • Our new paper: Extreme rainfall further endangers the world’s rarest great ape Dave Petley
    In November 2025, Cyclone Senyar generated extreme rainfall in parts of Sumatra, Indonesia, triggering thousands of landslides. Our new paper in the journal Current Biology demonstrates that these landslides might have a devastating impact on a critically endangered population of Tapanuli orangutan. In November 2025, Cyclone Senyar brought extreme rainfall to large parts of Sumatra in Indonesia. I have written about this on previous occasions – the rainfall triggered vast numbers of lan
     

Our new paper: Extreme rainfall further endangers the world’s rarest great ape

11 June 2026 at 07:19
Before and after satellite imagery of the impacts of Cyclone Senyar.

In November 2025, Cyclone Senyar generated extreme rainfall in parts of Sumatra, Indonesia, triggering thousands of landslides. Our new paper in the journal Current Biology demonstrates that these landslides might have a devastating impact on a critically endangered population of Tapanuli orangutan.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

In November 2025, Cyclone Senyar brought extreme rainfall to large parts of Sumatra in Indonesia. I have written about this on previous occasions – the rainfall triggered vast numbers of landslides.

In my line of work, we often focus on the landslide impacts on the landscape, on human lives and on infrastructure. We rarely consider the impacts on th eanimal population. This is certainly a weakness that the Cyclone Senyar event brings to focus.

Part of the area devastated by the landslides is that slopes around the Batang Toru rover, an area of forest that is home to a rare species of orangutang. These great apes, Pongo tapanuliensis, live in a habitat known as the West Block of Tapanuli. There are only 800 individuals left in the wild, a situation that is highly precarious. The loss of even a small number of adults could tip the species towards extinction.

I was a part of a consortium of scientists that considered the landslide impacts of Cyclone Senyar on the habitat of these orangutangs. The results have just been published in the journal Current Biology (Meijaard et al. 2026) – the paper is open access and published under a creative commons license.

This image, from the paper, shows the landslide impacts of Cyclone Senyar:-

Before and after satellite imagery of the impacts of Cyclone Senyar.
Before and after satellite imagery of the impacts of Cyclone Senyar. From: Meijaard et al. (2026).

In the study area of 71,161 hectares, the mapping indicates that there were 50, 185 individual landslides, covering a surface area of 8,303 hectares. This is about 11% of the forested area. We then estimate the likely loss of the orangutang population, which is likely to be in the range of 18-120 individuals, with a central estimate of 58 individuals. This is likely to have been a devastating loss for this highly endangered population.

This level of habitat loss might also be placing a severe pressure on the remaining population, so further fatalities are very possible through, for example, reduced food availability.

The intensity of the rainfall was almost certainly supercharged by climate change. The impacts of Cyclone Senyar are being replicated widely – and of course we are now in the northern hemisphere tropical cyclone season again.

Our paper makes some policy recommendations for this population of orangutans. First, the government of Indonesia needs to permanently protect this area of forest against mining , palm oil and hydropower developments. Ideally, the protected area should be expanded. Second, Indonesia needs support for biodiversity-recovery, hazard forecasting and ecological restoration planning.

Reference

Meijaard, E. … Petley. D. … et al. 2026, Extreme rainfall further endangers the world’s rarest great ape. Current Biology. https://doi.org/10.1016/j.cub.2026.05.029

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  • The 19 July 2025 multiple landslide event in Sancheong, South Korea Dave Petley
    On 19 July 2025, intense, long duration rainfall triggered over 550 landslides in Sancheong, South Korea, killing at least 10 people. On 19 July 2025, extremely heavy rainfall triggered multiple landslides in Sancheong, South Korea. This event has been described by a new paper (Nguyen et al. 2026) just published in the journal Landslides. The paper is behind a paywall, but this link should give you access at the time of writing. The core of the affected area is at [35.4333, 127.9111]
     

The 19 July 2025 multiple landslide event in Sancheong, South Korea

15 May 2026 at 07:22
Planet Labs image of a part of the area affected by landslides during heavy rainfall in Sancheong County, South Korea on 19 July 2025.

On 19 July 2025, intense, long duration rainfall triggered over 550 landslides in Sancheong, South Korea, killing at least 10 people.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

On 19 July 2025, extremely heavy rainfall triggered multiple landslides in Sancheong, South Korea. This event has been described by a new paper (Nguyen et al. 2026) just published in the journal Landslides. The paper is behind a paywall, but this link should give you access at the time of writing.

The core of the affected area is at [35.4333, 127.9111] (as usual, Landslides provides the location in degrees minutes and seconds when digital degrees is so much more useful – a pet frustration of mine!). This is a Planet Labs image of a part of the area, captured before the event. The marker is at the coordinate noted above:-

Planet Labs image of a part of the area affected by landslides during heavy rainfall in Sancheong County, South Korea on 19 July 2025.
Planet Labs image of a part of the area affected by landslides during heavy rainfall in Sancheong County, South Korea on 19 July 2025. Image copyright Planet Labs, used with permission. Image dated 10 July 2025.

And this is the same area after 19 July 2025:-

Planet Labs image of a part of the area affected by landslides during heavy rainfall in Sancheong County, South Korea on 19 July 2025.
Planet Labs image of a part of the area affected by landslides during heavy rainfall in Sancheong County, South Korea on 19 July 2025. Image copyright Planet Labs, used with permission. Image dated 23 July 2025.

And here is a slider to allow a comparison:-

Planet Labs image of a part of the area affected by landslides during heavy rainfall in Sancheong County, South Korea on 19 July 2025.Planet Labs image of a part of the area affected by landslides during heavy rainfall in Sancheong County, South Korea on 19 July 2025.
Images by Planet Labs.

Nguyen et al. (2026) have mapped 568 individual landslides triggered by this rainfall event, triggered by rainfall in the range of 498 – 619 mm over a c. 55 hour period. These landslides killed at least 10 people and caused damage to homes and infrastructure. It is estimated that the restoration costs are in the order of US$800 million.

In common with many other events of this type, the landslides are mainly shallow, translational failures in soil or regolith on steeper slopes. As I have frequently noted, such terrain is very susceptible to unusually intense rainfall events, which often trigger a cluster of landslides in close proximity. These often merge to form channelised debris flows. Nguyen et al. (2026) note however that their modelling indicates that it was a combination of the intensity of the rainfall and its duration that led to these failures.

As rainfall intensities increase due to climate change, we are seeing increasing numbers of these landslide clusters. I greatly welcome studies such as Nguyen et al. (2026) , which allow us to build understanding in each case.

Reference and acknowledgement

Nguyen, H.H.D., Song, C.H. & Kim, Y.T. 2026. Physically based data-driven analysis for large-scale investigation of the July 2025 rainfall-induced landslide in Sancheong, South KoreaLandslides. https://doi.org/10.1007/s10346-026-02778-x

Planet Team 20246. Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

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  • The 9 April 2026 landslide at Lamarain in Papua New Guinea Dave Petley
    Ten people were killed in a large landslide in Papua New Guinea triggered by heavy rainfall associated with Tropical Cyclone Maila. On 9 April 2026, a large landslide occurred at Lamarain in the Inland Baining LLG of Gazelle District in Papua New Guinea. The landslide was triggered by heavy rainfall associated with the passage of Tropical Cyclone Maila. Media reports indicate that ten people were killed by the landslide and that a further 18 people were injured. Baining is located at
     

The 9 April 2026 landslide at Lamarain in Papua New Guinea

17 April 2026 at 07:47
The landslide at Lamarain in Papua New Guinea

Ten people were killed in a large landslide in Papua New Guinea triggered by heavy rainfall associated with Tropical Cyclone Maila.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

On 9 April 2026, a large landslide occurred at Lamarain in the Inland Baining LLG of Gazelle District in Papua New Guinea. The landslide was triggered by heavy rainfall associated with the passage of Tropical Cyclone Maila.

Media reports indicate that ten people were killed by the landslide and that a further 18 people were injured. Baining is located at [-4.2548, 151.7811], so I assume that this is the general area.

Gaining information about landslides in the remote areas of Papua New Guinea is very challenging – the terrain is rugged and there is a high level of civil turmoil. But the best source of information is on the Facebook page of NBC East Britain, which has posted a helicopter video of the aftermath. This is a still from that video:-

The landslide at Lamarain in Papua New Guinea
The landslide at Lamarain in Papua New Guinea. Still from a video posted to Facebook by NBC East New Britain.

There are several interesting aspects of this landslide. First, the failure appears to have initiated high on the hillslope in an area that has a mix of forestry and cleared areas. The source appear to be quite large and deep-seated. This has transitioned into a disrupted debris slide / avalanche with a substantial amount of entrainment.

Note also the multiple other landslides in that area, all fresh, suggesting that the intense rainfall was sufficient to drive widespread failures. It is interesting to note though that is event did not involve multiple shallow landslides that combined to create a channelised debris flow.

The Post Courier reports that the Lamerain landslide occurred in two phases, the first at 6 am on 9 April 2026 and the second 24 hours later. However, other reports suggest that it occurred on 12 April 2026, underlying the challenges of properly understanding landslides in Papua New Guinea.

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  • Seismic Attenuation Techniques Reveal What Lies Beneath Taiwan Nathaniel Scharping
    Source: Geophysical Research Letters As seismic waves travel through Earth, they gradually lose energy, a process called attenuation. That energy loss doesn’t happen uniformly—some features in the crust sap far more energy from seismic waves than others. Researchers can map underground features by watching where seismic waves lose more or less energy. The Southern Array for the Lithosphere and Uplift of Taiwan Experiment (SALUTE) is doing just that, providing information that could lead to i
     

Seismic Attenuation Techniques Reveal What Lies Beneath Taiwan

11 May 2026 at 13:16
Three researchers huddle around camping equipment and scientific instruments in a grassy area on a foggy day.
Source: Geophysical Research Letters

As seismic waves travel through Earth, they gradually lose energy, a process called attenuation. That energy loss doesn’t happen uniformly—some features in the crust sap far more energy from seismic waves than others. Researchers can map underground features by watching where seismic waves lose more or less energy. The Southern Array for the Lithosphere and Uplift of Taiwan Experiment (SALUTE) is doing just that, providing information that could lead to improved seismic hazard planning in the country.

Lin et al. report attenuation results from SALUTE focused on the convergence between the Eurasian plate and the Luzon Arc, an understudied, geologically dynamic area where Earth’s crust is deforming. Using the overall attenuation rate and relative attenuation rates of P and S seismic waves, the authors imaged active faults, identified distinct lithologies, and better resolved the Luzon forearc block that sits just offshore of Taiwan.

The authors used data from the SALUTE high-density seismographic network, spanning December 2020 to December 2023, to construct both 2D and 3D attenuation models. They found clear changes in attenuation associated with major faults, as well as areas of high attenuation associated with fluid-rich, ductile zones in the lower crust that cause tectonic tremors. Their attenuation imaging additionally revealed that the Luzon forearc block, which had been poorly imaged in the past, dips northward and narrows as it nears the convergence zone.

The authors say their results agree well with previous velocity-based seismic imaging studies and show that attenuation can image features, such as transition zones, that were previously difficult to capture. Their data could also be useful for better understanding seismic hazard throughout the region, they note. (Geophysical Research Letters, https://doi.org/10.1029/2025GL121583, 2026)

—Nathaniel Scharping (@nathanielscharp), Science Writer

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Citation: Scharping, N. (2026), Seismic attenuation techniques reveal what lies beneath Taiwan, Eos, 107, https://doi.org/10.1029/2026EO260150. Published on 11 May 2026.
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  • The 10 December 2025 Huangci landslide in Gansu Province, China Dave Petley
    A new paper in the journal landslides (Yang et al. 2026) details the 6.8 million cubic metre Huangci Landslide in China, which was a reactivation on a slope that has suffered two other failures in recent decades. On 10 December 2025, failure occurred in the large Huangci landslide in Gansu Province, China. The event is described in a new paper (Yang et al. 2026) in the journal Landslides (this link should provide access even though the article is paywalled). The paper is fascinating as t
     

The 10 December 2025 Huangci landslide in Gansu Province, China

22 May 2026 at 07:36
An image from a drone showing the aftermath of the 10 December 2025 Huangci landslide in China.

A new paper in the journal landslides (Yang et al. 2026) details the 6.8 million cubic metre Huangci Landslide in China, which was a reactivation on a slope that has suffered two other failures in recent decades.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

On 10 December 2025, failure occurred in the large Huangci landslide in Gansu Province, China. The event is described in a new paper (Yang et al. 2026) in the journal Landslides (this link should provide access even though the article is paywalled). The paper is fascinating as this is a very complex slope with an interesting history of deformation, and because large failures do not usually occur in the winter months in this part of China.

The location of the Huangci landslide is [36.08983, 103.32412]. This is a Google Earth image of the site, captured in 2004:-

Google Earth image of the Huangci landslide in 2004.
Google Earth image of the Huangci landslide in 2004.

The geology consists of loess overlying mudstones. As the image above shows, the site had previously failed. The houses at the foot of the slope are the homes of people displaced in 1968 during the impoundment of the Liujiaxia Reservoir. Note also the farmland on the terrace behind the landslide. This is an arid area, so this farming requires extensive irrigation.

According to Yang et al. (2026), the failure that can be seen in the image above occurred on 30 January 1995. About 6 million cubic metres of rock and loess were involved, creating a landslide with a width of about 500 metres and a length of about 370 m.

The Huangci landslide failed again on 14 May 2006, this time with a volume of about 4 million cubic metres. The image below, captured in 2013, shows the aftermath:-

Google Earth image of the Huangci landslide in 2012.
Google Earth image of the Huangci landslide in 2012.

In this failure, 10 houses were destroyed.

The most recent failure of the Huangci landslide occurred on 10 December 2025. This time, a larger mass failed, creating a landslide with a volume of about 6.77 million cubic metres, a length of up to about 740 metres and a width of up to about 420 metres. There is a spectacular video on Youtube showing the aftermath of the failure:-

The still below gives an impression of the scale of the failure:-

An image from a drone showing the aftermath of the 10 December 2025 Huangci landslide in China.
An image from a drone showing the aftermath of the 10 December 2025 Huangci landslide in China. Still from a video posted to Youtube by 阿龍說牆內事.

According to Yang et al. (2026), this failure destroyed 39 houses plus a range of infrastructure that includes power transmission systems, irrigation systems, water supply systems and transportation facilities. The site had been successfully evacuated as a result of a community-operated early warning system.

As noted above, this is an unusual time of the year for a landslide of this type. However, Yang et al. (2026) conclude that the underlying driver is irrigation on the terrace upslope from the landslide, driving a rise in the groundwater and consequent progressive deformation of the slope. This led to weakening of the mudstones that were buttressing the failure, eventually triggering collapse.

Reference

Yang, Y. et al. 2026. The reactivated Huangci landslide at the Heifangtai terrace, Gansu Province, China, on December 10, 2025Landslides. https://doi.org/10.1007/s10346-026-02765-2.

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  • The Forensics of a Skyscraper-Sized Tsunami Matthew R. Francis
    In the early morning of 10 August 2025, a mountainside collapsed into the waters of Tracy Arm Fjord in southeastern Alaska. This massive landslide produced a tsunami that reached 481 meters on the opposite side of the fjord—higher than all but the world’s 14 tallest buildings—and registered on seismic detectors around the globe. For days after the slope collapsed, the waters of the fjord churned with a standing wave known as a seiche. This drone video shows a man paddling throu
     

The Forensics of a Skyscraper-Sized Tsunami

6 May 2026 at 13:15
A photo shows a mountainside with a large wedge of lighter-colored rock, above a churning channel of water. The foot of a glacier can be seen at the lower edge of the image.

In the early morning of 10 August 2025, a mountainside collapsed into the waters of Tracy Arm Fjord in southeastern Alaska.

This massive landslide produced a tsunami that reached 481 meters on the opposite side of the fjord—higher than all but the world’s 14 tallest buildings—and registered on seismic detectors around the globe. For days after the slope collapsed, the waters of the fjord churned with a standing wave known as a seiche.

This drone video shows a man paddling through the iceberg-filled Tracy arm fjord in the aftermath of a landslide. Credit: Bill Billmeier

This event was the second-largest tsunami ever recorded and the largest not linked to an earthquake. A new paper published in Science presented strong evidence that the Tracy Arm landslide was instead the result of the rapid retreat of South Sawyer Glacier, itself a consequence of global climate change.

“It’s like if you have a kid and they said they cleaned their room but really all they did was throw everything in the closet. As soon as you open that door, everything falls out.”

Nobody was harmed by the rockslide or tsunami, but cruise ships were scheduled to visit the fjord later that morning. If the collapse had happened just a few hours later, it could have been disastrous.

“While the [South Sawyer] Glacier is in the fjord, it’s supporting those valley walls, like the buttresses on a cathedral,” said Daniel Shugar, a geomorphologist at the University of Calgary who led the study. “As that glacier retreated over the last few decades, it retreated just past the spot that did fail. It’s like if you have a kid and they said they cleaned their room but really all they did was throw everything in the closet. As soon as you open that door, everything falls out.”

This animation shows an overhead view of the 10 August 2025 Tracy Arm landslide. Credit: Patrick Lynett, University of Southern California

In other words, the glacier that carved the fjord in the first place was also holding its slopes in place, and the ice’s retreat under warming temperatures exposed rock that became vulnerable to crumbling. The proximate cause of the landslide might have been something else—as Shugar noted, rainfall is plentiful in that part of Alaska, which could have weakened the fjord’s walls further—but it might also have been a combination of small, individually insignificant factors. In any case, the removal of that glacial “closet door” was what made the collapse and tsunami possible.

“We know that steep slopes are very sensitive to the things that climate [change] is exacerbating, whether it’s losing permafrost, glacier retreating, or more water in the soil,” said glaciologist Leigh Stearns of the University of Pennsylvania, who was not involved with the Tracy Arm study. “Often, we think of glacier retreat as a long and continuous thing, but [it] can trigger sudden catastrophic events.”

This aerial photo shows the highest run-up resulting from the 10 August 2025 landslide-triggered tsunami in Tracy Arm. It was captured during a U.S. Geological Survey field reconnaissance overflight on 13 August 2025. Credit: John Lyons/U.S. Geological Survey.

The researchers shared their findings at a press briefing on Wednesday at the European Geosciences Union 2026 General Assembly.

Debuttressing and Slope Instability

The Tracy Arm tsunami, like the record-setting Lituya Bay 524-meter megatsunami in 1958, was so dramatic in part because it happened in a fjord. The steep sides of the relatively narrow channel concentrated the energy generated by the rockfall into water.

A drone video shows the tsunami-affected part of the fjord, including the highest run-up area and the landslide itself. Credit: Bill Billmeier

Unlike Lituya Bay, which resulted from an earthquake, Tracy Arm provided very little seismic warning before the slope collapsed, requiring forensic work to determine what caused it.

Shugar noted that South Sawyer Glacier had retreated by roughly 500 meters in the spring of 2025 alone, on top of the general trend of shrinking and thinning over the decades. And it’s not alone: Interferometric synthetic aperture radar (InSAR) images taken by satellites indicate that many slopes in Alaska and beyond are in motion, pointing to potential future danger.

“Not every single one, but it seems like a huge majority of [shifting slopes] are above the lower parts of thinning glaciers,” Shugar said. He described this phenomenon as “debuttressing,” as in losing the glacial buttress holding a slope up. He added, “I think in the next 5 years or so, we’ll probably have a much better understanding of just how and how quickly slopes respond to that debuttressing.”

Threats, Hazards, and Climate Change

“We were unbelievably lucky that the [tsunami] occurred with the timing that it did, and not 5 hours later.”

Most tsunamis are set in motion by earthquakes and travel across the open ocean, wreaking their destruction when they reach shallower water near coasts; the word “tsunami” means “harbor wave” in Japanese. The Tracy Arm tsunami joined the ranks of other landslide-driven tsunamis, like the ones in Taan Fiord (Alaska) and Dixon Fjord (Greenland), in being linked to human-driven climate change. Beyond the immediate impact of the waves, this category of hazard requires rethinking potential risks from abrupt catastrophes like debuttressing as well as slower effects such as sea level rise.

“The risk to any particular cruise ship [from a tsunami] on any particular day is very low,” Shugar said. “We were unbelievably lucky that the [tsunami] occurred with the timing that it did, and not 5 hours later. The risk certainly still could be increasing as we build new settlements, new mining camps, or new oil and gas infrastructure.”

Both Shugar and Stearns highlighted the importance of learning lessons from Tracy Arm and related events.

“Climate is a threat multiplier, and the research is really forcing us to look at these cascading hazards,” Stearns said. Tracy Arm “is one example of this: Small slow changes can trigger big events. Hopefully, we don’t need so many disasters to spur some change.”

A drone video shows Sawyer Island in the Tracy Arm Fjord and evidence of the tsunami on the fjord walls. Credit: Bill Billmeier

—Matthew R. Francis (@BowlerHatScience.org), Science Writer

Citation: Francis, M. R. (2026), The forensics of a skyscraper-sized tsunami, Eos, 107, https://doi.org/10.1029/2026EO260140. Published on 6 May 2026.
Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

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This aerial photo shows the north side of Alaska’s Tracy Arm Fjord in the aftermath of the 2025 landslide and tsunami. The lighter-colored rock is the exposed surface, where the mountainside collapsed and fell into the water. The foot of South Sawyer Glacier is visible at lower right; in decades past, the ice extended much farther and was thick enough to hold the rock slopes in place. Credit: Cyrus Read/U.S. Geological Survey
  • ✇Eos
  • A New Approach Can Better Predict Debris Flow Hazards Years After Fires Grace van Deelen
    Months after wildfires eliminate vegetation that holds hillside sediment together, debris flows—destructive landslides that carry bulky material down once-stable slopes—can devastate infrastructure, taking out roads and buildings in their wake. Though the U.S. Geological Survey (USGS) creates hazard predictions used to warn communities of the risk of these postfire debris flows, those predictions haven’t fully considered how recovering vegetation reduces risk over time—until now.
     

A New Approach Can Better Predict Debris Flow Hazards Years After Fires

19 May 2026 at 12:59
Debris, including downed trees and building materials, in a valley below a mountain.
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Months after wildfires eliminate vegetation that holds hillside sediment together, debris flows—destructive landslides that carry bulky material down once-stable slopes—can devastate infrastructure, taking out roads and buildings in their wake.

Though the U.S. Geological Survey (USGS) creates hazard predictions used to warn communities of the risk of these postfire debris flows, those predictions haven’t fully considered how recovering vegetation reduces risk over time—until now.

A new study published in Geosphere presents a new way to calculate postfire debris flow risk that takes vegetation recovery into account. The USGS will begin using the new method this wildfire season to create more accurate maps of debris flow hazard in the years after a fire.

“I’m so appreciative that the focus on how the debris flow hazard changes over time after fire is being addressed,” said Nancy Calhoun, a geologist and postwildfire debris flow program manager at the Washington Geological Survey who was not involved in the new study. Calhoun said she relies on the USGS hazard assessments for virtually everything her job requires.

“We’re glad to have a way that we can help our partners moderate those situations where the hazard has decreased,” said Andrew Graber, a geologist at the USGS Landslide Hazards Program and lead author of the new study.

Assessing Hazard, Again

After a wildfire, the USGS creates hazard maps that incorporate information about soil type, steepness, and burn severity (how much vegetation has been lost) to show where the risk of a debris flow may be elevated.

Then, the agency distributes this guidance to the National Weather Service, which uses it to set rainfall thresholds: levels of rainfall at which a debris flow becomes likely. State, county, and city agencies use those rainfall thresholds to issue warnings or take action when rainfall is imminent, for example, by closing highways or triggering evacuations.

“That left us with some uncertainty when we started to get further away in time from the fire.”

The methods used to create the USGS maps, however, historically relied on a snapshot of the burned area taken just after the fire, and the maps weren’t updated to reflect conditions as vegetation grew back and began holding soil in place again.

That led to situations where public safety decisions were made on the basis of outdated maps and rainfall thresholds. For example, concern over debris flows after the 2020 Grizzly Creek Fire in Colorado led to several closures of Interstate 70 in 2022, but the debris flows never happened.

“What [the original assessments] didn’t capture is how the vegetation came back,” Graber said. “That left us with some uncertainty when we started to get further away in time from the fire.”

Intense rainfall in July 2025 triggered a debris flow near Dayton, Wyo., in the 2024 Elk Fire burn area. Credit: USGS, Public Domain

To test an improved method for these hazard assessments, Graber and the research team incorporated satellite imagery of 12 burned areas that showed the degree of vegetation recovery right after the fire, 1 year after the fire, and 2 years after the fire. Then, they tested their new method by comparing its predictions to rainfall and debris flow data from the 12 burned areas.

The updated method better reflected what had actually happened after the fires, reducing the number of unnecessary warnings without missing real-world debris flows.

Risk Recalibration

The USGS plans to begin using their new workflow to create hazard maps for some higher-profile fires during the coming wildfire season.

“It’s a really important question: Are we still worried about this burn scar?”

That’s exciting for Calhoun. As part of her job, she’s in constant contact with emergency managers who periodically ask how worried they should be about debris flows in areas that burned years ago. “It’s a really important question: Are we still worried about this burn scar?” she said.

Right now, Calhoun has no data to point to in the years after a fire to give an updated answer to that question. Using the new method from Graber and the research team, she will.

“Because they’re using satellite [imagery] and repeatable quantitative methods to look at these burn scars over time, we’ll actually be able to say something useful and informed about vegetation recovery,” she said.

Having a deeper understanding of how debris flow risk evolves over time is especially important because debris flows themselves are becoming a greater risk to the public as a result of increasingly intense wildfires and rainstorms. In addition, more accurate assessments can reduce warning fatigue, which occurs when too many false alarms lead to people ignoring or opting out of alerts.

Graber hopes he and the USGS will continue to improve their methods for assessing debris flow hazards by collecting more debris flow data across the country and improving the underlying equation for hazard assessments so that it better reflects the unique conditions of different ecosystems in the United States. USGS researchers also published a new study in March presenting a method to generate maps of where debris flows might travel if they do occur.

“It’s a big year for USGS’s useful postfire products,” Calhoun said.

—Grace van Deelen (@gvd.bsky.social), Staff Writer

This news article is included in our ENGAGE resource for educators seeking science news for their classroom lessons. Browse all ENGAGE articles, and share with your fellow educators how you integrated the article into an activity in the comments section below.

Citation: van Deelen, G. (2026), A new approach can better predict debris flow hazards years after fires, Eos, 107, https://doi.org/10.1029/2026EO260160. Published on 19 May 2026.
Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
  • ✇Eos
  • Fatal landslides in April 2026 Dave Petley
    In April 2026 I recorded 36 fatal landslides causing 90 fatalities, the lowest monthly total for 2026 to date. This is my regular update for the number of fatal global landslides, focusing on March 2026. As usual, this data has been collected in line with the methodology described in Froude and Petley (2018) and in Petley (2012). References are listed below – please cite these articles if you use this analysis. Data presented in these updates should be treated as being provisional at thi
     

Fatal landslides in April 2026

8 May 2026 at 07:49
The landslide at Lamarain in Papua New Guinea

In April 2026 I recorded 36 fatal landslides causing 90 fatalities, the lowest monthly total for 2026 to date.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

This is my regular update for the number of fatal global landslides, focusing on March 2026. As usual, this data has been collected in line with the methodology described in Froude and Petley (2018) and in Petley (2012). References are listed below – please cite these articles if you use this analysis. Data presented in these updates should be treated as being provisional at this stage as I will reanalyse them prior to formal publication, and other events will emerge.

The headline figures are as follows:

March 2026: 36 fatal landslides causing 90 fatalities;

This is an interesting result, unusually showing that fatal landslides in April were substantially lower than for any of the preceding months in 2026. This is the updated annual chart by month:-

The number of global fatal landslides in 2026 by month to the end of April.
The number of global fatal landslides in 2026 by month to the end of April.

Loyal readers will know that I like to present the running total using pentads (five day blocks). This is the cumulative total pentad graph to the end of Pentad 24 (which captures all of the events to the end of April):-

The cumulative total number of global fatal landslides in 2026 by pentad to the end of April.
The cumulative total number of global fatal landslides in 2026 by pentad to the end of April.

Thus, whilst April 2026 was unexceptional compared with the previous months of this year, the number of fatal landslides was still above the long term mean. Overall, 2026 continues to run extremely hot, exceeding even the record-breaking year of 2024.

We now start to enter the crucial period of much higher global fatal landslide occurrence. Whilst in the long term dataset this acceleration typically occurs in June (or even July), in recent years it has happened in May, as the 2024 line shows. I will watch with great interest to see what happens this month.

As I always stress, the occurrence of fatal landslides prior to the South and East Asia rainy seasons is not a predictor of what will happen in that period. Interestingly, the WMO is forecasting a below average summer monsoon in South Asia.

References

Froude, M. and Petley, D.N. 2018.  Global fatal landslide occurrence from 2004 to 2016.  Natural Hazards and Earth System Sciences 18, 2161-2181.

Petley, D.N. 2012. Global patterns of loss of life from landslidesGeology 40 (10), 927-930.

Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
  • ✇Eos
  • Let’s Not Forget About Long Droughts Stefan Kollet
    Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Water Resources Research In the March 2026 issue of Water Resources Research, Zhang et al. [2026] interrogate conceptual hydrologic models’ ability to capture prolonged drought dynamics. The Australian Millennium drought serves as an example in the study. The results are quite sobering because the vast majority of more than 40 models fail. Unfortunately, calibration doesn’t generally help either and might
     

Let’s Not Forget About Long Droughts

5 May 2026 at 12:00
Map of the study region with a graph.
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Water Resources Research

In the March 2026 issue of Water Resources Research, Zhang et al. [2026] interrogate conceptual hydrologic models’ ability to capture prolonged drought dynamics. The Australian Millennium drought serves as an example in the study. The results are quite sobering because the vast majority of more than 40 models fail. Unfortunately, calibration doesn’t generally help either and might result in massive overfitting. In essence, conceptual models miss deep aquifer storage components and associated hydrodynamic processes leading to a lack of time scales important in drought modeling. The study is a constructive reminder that model parsimony is not necessarily a good thing and that detailed representation of complex physical processes is part of hydrologic sciences.

Citation: Zhang, Z., Fowler, K., & Peel, M. (2026). Can conceptual rainfall-runoff models capture multi-annual storage dynamics? Water Resources Research, 62, e2025WR042226. https://doi.org/10.1029/2025WR042226

—Stefan Kollet, Editor, Water Resources Research

Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
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