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“Near-miss” Tsunami in Alaskan Cruise Area Offers Lessons for Steep Landscapes Near Glaciers

As glaciers retreat in warming regions, the risk of related hazards can increase, and improved monitoring may help reduce some of those dangers, according to a new study.

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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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  • The prospects for the 2026 monsoon in South Asia Dave Petley
    Forecasts for the 2026 South Asia monsoon are for below average rainfall, but some of the most landslide prone areas of India may receive totals that are above average. As usual, we are now starting to see the number of reported global fatal landslides increase as the northern hemisphere rainy season commences. In recent days, there have been fatal floods and landslides across several provinces of mainland China as well as landslides on the pilgrimage route to Kederath in northern India.
     

The prospects for the 2026 monsoon in South Asia

21 May 2026 at 07:25
The WMO 2026 South Asia monsoon forecast.

Forecasts for the 2026 South Asia monsoon are for below average rainfall, but some of the most landslide prone areas of India may receive totals that are above average.

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

As usual, we are now starting to see the number of reported global fatal landslides increase as the northern hemisphere rainy season commences. In recent days, there have been fatal floods and landslides across several provinces of mainland China as well as landslides on the pilgrimage route to Kederath in northern India.

The global pattern is dominated by the South Asia (southwest / summer) monsoon, so it is interesting at this point to to consider the prospects for this year. The monsoon itself is expected to start in SW India next week, timing that is normal. It will then build over the following month or so.

The current forecast for the monsoon itself is that the total rainfall is likely to be below average. This is the WMO forecast:-

The WMO 2026 South Asia monsoon forecast.
The WMO 2026 South Asia monsoon forecast from the WMO.

The map shows below average precipitation for much of South Asia. The IMD also forecasts below average rainfall.

Of course, in landslide terms we are interested mainly in SW India (Kerala), which has a below average forecast, and the mountainous areas of Pakistan, India, Nepal, Bhutan and Bangladesh. Much of this is also forecast to receive below average precipitation, but note the above average forecast for parts of northern India (Jammu and Kashmir, Himachal Pradesh) and NE India (Sikkim, Arunachal Pradesh). These are some of the most landslide-prone areas of India, suggesting that we may well see substantial landslide challenges in these areas.

The caveat of course is that monsoon-triggered landslides are sensitive to rainfall intensity as well as rainfall magnitude. A below average monsoon can bring intense rainfall events that trigged catastrophic landslides. Unfortunately, the forecasts cannot resolve this issue.

As an aside, the next few days in the European Alps will be interesting. We are about to see a few days of unusually high temperatures, which are likely to drive a wave of snowmelt and permafrost thawing. Given the time of year, this could well trigger extensive rockfall activity.

Unfortunately, by the time I get to Switzerland in nine days the weather is forecast to have reverted to cool drizzle!

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  • Landslides are New Zealand’s most expensive natural hazard, and the costs are rising quickly Dave Petley
    New evidence from the Natural Hazards Commission – Toka Tū Ake (NHC) shows that landslides are now New Zealand’s most costly natural hazard. New Zealand is a country that is prone to a range of natural hazards. Located on a series of major fault systems, earthquakes cause high levels of loss. The country is also volcanically active, with occasional tragedies. Heavy rainfall brings floods. To share the cost of these perils, following the 1942 Wairarapa earthquakes, the New Zealand go
     

Landslides are New Zealand’s most expensive natural hazard, and the costs are rising quickly

14 May 2026 at 07:16
Here be landslides - typical landslide-prone terrain in New Zealand.

New evidence from the Natural Hazards Commission – Toka Tū Ake (NHC) shows that landslides are now New Zealand’s most costly natural hazard.

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

New Zealand is a country that is prone to a range of natural hazards. Located on a series of major fault systems, earthquakes cause high levels of loss. The country is also volcanically active, with occasional tragedies. Heavy rainfall brings floods.

To share the cost of these perils, following the 1942 Wairarapa earthquakes, the New Zealand government established the Earthquake Commission (EQC) in 1945, initially focusing on earthquakes and war damage, but subsquently expanded to cover other natural hazards.

In the subsequent years, the EQC has evolved into the Natural Hazards Commission – Toka Tū Ake (NHC), with a purpose “to reduce the impact of natural hazards on people, property, and the community”. Essentially it operates as a financial pool, with home owners paying a levy on top of their insurance to generate the fund. In the event of a loss, the fund pays for the rebuild costs up to a cap (currently NZ$300,000); the remainder is then covered by the property’s insurance. Claims are funded directly from the pool, with reinsurance cover and ultimately a government guarantee in place to ensure that there are sufficient funds.

In reality, NHC does much more than this, acting to manage and settle claims, and to understand the range of hazards to which New Zealand is prone.

In the last few days, a range of media outlets in New Zealand have been reporting new data from NHC about losses from natural hazards in New Zealand. This is the headline from 1News:

“Landslides are New Zealand’s most expensive natural hazard – and new data reveals a sharp rise in damage claims and growing risks to homes, infrastructure and communities.”

In total, since 2021 NHC has received 13,000 landslide claims and has paid out NZ$322 million (US$191 million). New Zealand is seeing an abrupt increase in landslide losses, driven primarily by increasingly frequent high magnitude rainfall events. NHC is urging property owners to undertake preventative maintenance and to be aware of the limitations of EQC cover.

Here be landslides - typical landslide-prone terrain in New Zealand.
Here be landslides – typical landslide-prone terrain in New Zealand.

In common with many other places, these landslide hazards represent a major challenge to New Zealand. The landscape has many dormant landslides that are being reactivated by these increased rainfall events, and many new failures are also occurring. But, generating reliable risk maps for landslides remains a major challenge. This needs to be a major research focus in the coming years. It will require better understanding of triggering events (rainfall and earthquakes primarily); of the initiation processes within the slope; of runout / debris mobility; and of vulnerability and consequent losses. It is probably true to say that in all of these areas, landslide research lags behind that of earthquakes and floods, primarily because of a lack of long term investment.

In many countries, landslides are not an insured risk for this reason. On its own, this will be a major challenge that must be addressed. For those countries in which landslides are insured, we need quickly to get up to speed.

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  • The Cheekeye Debris Barrier Project Dave Petley
    In British Columbia a CAN$115 million project is almost complete to mitigate the risk posed by debris flows to the town of Squamish. Upstream of the town of Squamish in British Columbia, Canada, an extraordinary project is underway to mitigate the risk of debris flows. Known as the Cheekeye Debris Barrier Project, the scheme involves the construction of a concrete barrier that is 24 metres high across the Cheekeye Fan, designed to catch debris flows with a volume up to 2.4 million cu
     

The Cheekeye Debris Barrier Project

20 May 2026 at 08:15
A render of the completed Cheekeye Debris Barrier.

In British Columbia a CAN$115 million project is almost complete to mitigate the risk posed by debris flows to the town of Squamish.

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

Upstream of the town of Squamish in British Columbia, Canada, an extraordinary project is underway to mitigate the risk of debris flows. Known as the Cheekeye Debris Barrier Project, the scheme involves the construction of a concrete barrier that is 24 metres high across the Cheekeye Fan, designed to catch debris flows with a volume up to 2.4 million cubic metres of debris.

The project is almost complete, with hand-over expected in the summer of this year. There is an excellent article about the project on The Tyee website, which includes some very interesting images of the structure. The estimated cost of the project is around CAN$115 million. The location of the Cheekeye Debris Barrier Project is [49.79417, 1123.10878]. This is a render of the final form of the barrier (but take a look at the images of the almost completed structure too):

A render of the completed Cheekeye Debris Barrier.
A render of the completed Cheekeye Debris Barrier. Image via the District of Squamish.

This is a fascinating project that makes a great case study for teaching, not least because both the detailed design considerations and the regulatory process for approving the programme are available in detail.

In terms of the detailed design considerations, there is an excellent open access paper in the Canadian Geotechnical Journal (Lesueur et al. 2025) that provides a very comprehensive analysis of the estimation of the potential volume and mobility of the debris flows on the Cheekeye Fan, and of the considerations that went into the final deisign of the structure.

In terms of the approval process, the District of Squamish has an online archive of documents and Council minutes that extends back to 2003.

I would highlight the challenges around determining the optimal size of a barrier of this type. The team has been balancing risk against cost, following the principle as outlined in Lesueur et al. (2025):-

“The local government specifies that tolerable debris-flow risks be reduced “as low as reasonably practicable” (ALARP), defined in this project as the point where the cost of additional mitigation measures is grossly disproportionate to the benefits gained.”

Thus, the barrier is not designed to stop the maximum credible debris flow, which is 5.5 million cubic metres (more than double the design event). This is pragmatic engineering at its best, and the Cheekeye Debris Barrier Project provides the level of detail that allows the decision-making process to be fully understood.

Reference

LeSueur, P. et al. 2026. Risk-informed design of debris-flow mitigation at Cheekeye FanCanadian Geotechnical Journal62: 1-16. https://doi.org/10.1139/cgj-2023-0008

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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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Potential landslides and liquefaction from the 8 June 2026 M=7.8 earthquake offshore Mindanao in the Philippines

8 June 2026 at 07:19
Initial Pager map of landslide hazard from the 8 June 2026 earthquake offshore Mindanao in the Philippines.

Initial analyses suggest that the earthquake this morning has the potential to have triggered significant numbers of landslides and areas of liquefaction.

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

At the time of writing, the impacts of the M=7.8 earthquake that occurred offshore the south coast of Mindanao in the Philippines remain unclear. Initial reports in the local press suggest 15 fatalities so far, but as always it could be the case that there is no information from those areas most seriously impacted.

The USGS Pager site is the best source of information about potential landslide impacts, bearing in mind there is a high level of uncertainty. This estimates that the area exposed to landslides is at the high end of the “significant” scale and that the population exposed to landslides lies in the 1,000 to 10,000 people range. This is the Pager landslide hazard map:-

Initial Pager map of landslide hazard from the 8 June 2026 earthquake offshore Mindanao in the Philippines.
Initial Pager map of landslide hazard from the 8 June 2026 earthquake offshore Mindanao in the Philippines. Source: USGS.

The area with the highest level of landslide hazard is remote and rural, so we may not get good information from this area for a while.

The potential for liquefaction may be even more serious, with a broad swathe having a high level of hazard:-

Initial Pager map of liquefaction hazard from the 8 June 2026 earthquake offshore Mindanao in the Philippines. Source: USGS.
Initial Pager map of liquefaction hazard from the 8 June 2026 earthquake offshore Mindanao in the Philippines. Source: USGS.

Past earthquakes have generated large liquefaction-related landslides on low angle slopes, with devastating effects. Hopefully, there won’t have been an event on this scale in Mindanao.

One final point to note is that the Philippines is just entering the typhoon season. Fortunately, Mindanao is sufficiently far south to be away from the main typhoon zone. However, these storms are so large that they can bring very heavy rainfall – see for example Typhoon Bopha in 2012. A similar event this year could have very significant consequences.

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  • How Wildfires Worsen Flood Risk Nathaniel Scharping
    Source: Water Resources Research Wildfires can increase flooding risks in and downstream of burned areas by removing vegetation and disturbing hydrologic processes. As the climate changes, the severity of both wildfires and heavy rainfall events is increasing, meaning flooding is likely to become more severe in the near future. Better understanding how, and by how much, wildfires change flood risk is important for disaster and infrastructure planning for communities around the country. Ca
     

How Wildfires Worsen Flood Risk

30 April 2026 at 12:54
A rocky stream flows through a landscape of burned trees. A mountain is visible in the background.
Source: Water Resources Research

Wildfires can increase flooding risks in and downstream of burned areas by removing vegetation and disturbing hydrologic processes. As the climate changes, the severity of both wildfires and heavy rainfall events is increasing, meaning flooding is likely to become more severe in the near future. Better understanding how, and by how much, wildfires change flood risk is important for disaster and infrastructure planning for communities around the country.

Canham and Lane used streamflow data from the U.S. Geological Survey’s National Water Information System and precipitation data from the NOAA Analysis of Record for Calibration product to identify storms and quantify their effects across seven burned watersheds in the western United States.

To make the most of the limited data on flooding in the years following wildfires, the researchers created a paired-storms framework: They identified postfire peak flows (PFPFs), defined as the five highest peak flows within 3 years of a wildfire across seven watersheds. Then, for each precipitation event causing a PFPF, they looked for storms with similar characteristics (or paired storms) that occurred before the wildfire. Storm characteristics used for pairing included the season in which the storm occurred, recent precipitation, and precipitation depth, duration, and peak intensity.

The researchers found significantly elevated peak flows after wildfires in many cases, underlining the risks to communities following wildfires and validating their approach for use elsewhere.

Altogether, the authors found 26 PFPF events, including 20 with paired storms occurring before wildfires. For 75% of the postfire storms, their peak flows were 2 or more times greater than prefire peak flows. PFPFs were most likely to happen in the first year after a wildfire and typically occurred following storms that were centered upstream of the watershed centroid, were uniform in shape, and fully covered the watershed and burned area, the authors reported. They also found some evidence that the first storm in the year immediately following a fire has a higher-than-expected chance of producing a PFPF.

Future work could look more deeply at the characteristics of storms occurring over burned areas, such as storm direction and watershed recovery, and could apply the automated methods to more burned watersheds and storm events to enhance the robustness of the work, the authors say. (Water Resources Research, https://doi.org/10.1029/2025WR040693, 2026)

—Nathaniel Scharping (@nathanielscharp), Science Writer

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Citation: Scharping, N. (2026), How wildfires worsen flood risk, Eos, 107, https://doi.org/10.1029/2026EO260133. Published on 30 April 2026.
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  • 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.
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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
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Four days of extreme rain in Indonesia killed 7% of world’s rarest great apes, study finds

10 June 2026 at 16:18

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© Photograph: Nature Picture Library/Alamy

© Photograph: Nature Picture Library/Alamy

© Photograph: Nature Picture Library/Alamy

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