{"root":"n-XfjsAU","nodes":{"n-PdziiQ":{"type":"image","data":{"image":"r-UYZKYR"}},"n-SK506m":{"type":"storycover","data":{"type":"minimal","title":"August 2026 Nepal Trishuli Flood","summary":"Center for Land Surface Hazards (CLaSH) ","byline":"contact@geoclash.org (last updated 2 September 2026)","titlePanelVerticalPosition":"top","titlePanelHorizontalPosition":"start","titlePanelStyle":"gradient"},"config":{"isHidden":false},"children":["n-PdziiQ"]},"n-5k34sW":{"type":"navigation","data":{"links":[{"nodeId":"n-IZ9WXf"},{"nodeId":"n-I0jGyd"},{"nodeId":"n-zExJn9"},{"nodeId":"n-lrQnWA"},{"nodeId":"n-sbHqOe"},{"nodeId":"n-BA88wg"},{"nodeId":"n-wifAll"},{"nodeId":"n-0xDlGZ"},{"nodeId":"n-DN0GBR"},{"nodeId":"n-NuiSIY"},{"nodeId":"n-tb9oo8"}]},"config":{"isHidden":false}},"n-SU5rux":{"type":"text","data":{"text":"This is a live document and will be updated periodically. This StoryMap is intended to collect and share early scientific assessments of this event. We intend to provide regular updates (approximately every two days at the moment), so please check back again for more information.","type":"paragraph"}},"n-CSUaLF":{"type":"text","data":{"text":" Last updated: 19 September 2026","type":"paragraph"}},"n-bKYNPE":{"type":"text","data":{"type":"paragraph","text":"","textAlignment":"center"}},"n-xOKjG5":{"type":"text","data":{"type":"paragraph","text":"Join us at the American Geophysical Union (AGU) Fall Meeting for a newly added session: 2026 Nepal Debris Avalanche and Flash Flood","textAlignment":"center"}},"n-kgAVNL":{"type":"button","data":{"text":"Learn more about the AGU Session","link":"","alignment":"center"}},"n-IZ9WXf":{"type":"text","data":{"type":"h2","text":"1.0 Overview"}},"n-xpCNqr":{"type":"image","data":{"caption":"Upper reaches of the Lhende Khola-Bhote Koshi river system. Top: Regional overview showing Langtang Lirung, the mountain above the collapsed initiation site, and the main Trishuli River (blue). Middle: The upper reaches of the Lhende Khola River (teal) and the initiation site immediately below Langtang Lirung. The collapsed glacier and rock mass is highlighted in yellow, with the approximate flow path shown as a dashed blue line. Green circles mark small barrier lakes that formed in the aftermath of the flood. Inset shows the topographic profile of the region. Below: Satellite images of the source area acquired 2 days before and 2 days after the collapse. The annotated image delineates the approximate boundary of glacier (blue) and rock, with the entire collapsed portion in red. Approximate location: 28.292511°N, 85.530220°E. Image sources: Planet Labs PBC with 3.7 meter resolution.","image":"r-lHD1hM"},"config":{"size":"float","floatAlignment":"end"}},"n-OyU2xB":{"type":"text","data":{"type":"paragraph","text":"On the morning of August 26, 2026 (Nepal local time), a catastrophic debris flood swept through central Nepal along the Lhende Khola–Bhote Koshi/ Trishuli river system, causing significant damage across three districts (Rasuwa, Nuwakot and Dhading). The flood likely began with a large rock-ice avalanche near the Langtang Lirung and Tsangbu Ri mountain peaks. This rock and glacier collapse was observed in satellite imagery and recorded as a magnitude 5.2 seismic event (earthquake). The flood moved exceptionally fast, was sediment-laden, and extreme in scale. At Galchhi (27.7961°N, 85.0003°E), roughly 88 km downstream from the source, the Trishuli reportedly rose by approximately nine meters (28 ft) in only 30 minutes. The speed of the flood overwhelmed some of Nepal’s automatic flood-monitoring stations installed in the upper reaches of the Trishuli, sweeping them away before they could send a warning, leaving communities without any advance warning."}},"n-RW3LIq":{"type":"text","data":{"type":"paragraph","text":"As of 9:00 NPT on 1 September 2026, the National Disaster Risk and Reduction and Management Authority (NDRRMA) has reported the death toll has risen to 987, with 3,916 individuals still missing, making this one of the deadliest documented Himalayan flood events. "}},"n-lTFomU":{"type":"text","data":{"type":"paragraph","text":"Additionally, the Prithvi Highway, which serves as a key supply chain route for Kathmandu, has shut down due to a portion of the road collapsing because of the floods. The road collapsed near Krishnabhir, which also limits the access from Kathmandu to the affected region, is severely damaged and it is uncertain if/when the road will be repaired. The United National reports that parts of the severely affected districts, like Nuwakot and Rasuwa, are unable to receive assistance. "}},"n-0kNQvv":{"type":"text","data":{"type":"paragraph","text":"Initial seismic analysis estimates the avalanche contained between 197 - 492 million cubic meters of ice and rock. Even the low estimates of around 200 million cubic meters would make this the largest rock-ice avalanche ever recorded."}},"n-nUovyG":{"type":"text","data":{"type":"paragraph","text":"This event follows a previously destructive flood that struck the same Rasuwa district in July 2025, causing significant damage and raising alarms about the vulnerability of the communities and infrastructure in this valley to floods.  "}},"n-4pB0i7":{"type":"text","data":{"type":"paragraph","text":"Additionally, since the initial flood event, two lakes visible on satellite imagery have formed due to blockage of the river system by flood debris, which causes a risk of additional flooding and damages in the downstream areas, potentially worsened by the forecasted rainfall expected to arrive in the coming days. One of the lakes, measuring approximately 770 meters along its major axis, formed within the Lhende Khola River bank. The other, measuring approximately 530 meters along its major axis, formed just below the collapsed glacier. As of the morning of August 28, reports from researchers in China indicated that the lake forming along the Lhede Khola River began to overflow naturally and is no longer considered to be a significant risk.  However, seismic signals suggest more flooding along the Trishuli as recently as August 29 - as posted by Kristen Cook on BlueSky - but little is yet known about this flooding (though it seems much smaller than the devastating flood on August 26). Researchers are keeping an eye on these lakes as the situation continues to evolve, considering the potential risk for further outburst flooding. "}},"n-6BHAhV":{"type":"text","data":{"type":"paragraph","text":"
"}},"n-X1oyyo":{"type":"image","data":{"image":"r-PfURI5","caption":"Overview of the source area from satellite imagery taken on 28 August 2026. Imagery shows two lakes forming after the initial debris flow near the source area.  One lake formed within the Lhende-Khola River bank. Approximate location: 28.332916°N, 85.482467°E. just below the collapsed glacier. Approximate location: 28.292884°N, 85.510942°E. Image sources: Planet Labs PBC."}},"n-s4OQ1H":{"type":"text","data":{"type":"paragraph","text":"
"}},"n-G4oO8B":{"type":"video","data":{"video":"r-8J9m7q","thumbnail":"r-PMycKU","caption":"Drone video of the Lhende Khola debris dam and lake. Shared by Chengdu University of Technology (CDUT), credit CCTV."}},"n-I0jGyd":{"type":"text","data":{"type":"h2","text":"2.0 Impacts along the flooding corridor"}},"n-gTV6Ge":{"type":"text","data":{"type":"paragraph","text":"The flood entered Nepal through the Lhende Khola-Bhote Koshi river system near Rasuwagadhi (28.2774°N, 85.3777°E) and traveled downstream into the Trishuli River, affecting  Rasuwa and Nuwakot districts most severely, but Dhading, Gorkha and Chitwan districts are also significantly affected. "}},"n-DhlFgf":{"type":"text","data":{"type":"paragraph","text":"Timure (28.2555°N, 85.3702°E), near the Nepal–China border, was the first and one of the worst-hit settlements. Much of Timure Bazaar was swept away, together with homes, shops, and hundreds of vehicles near the customs checkpoint. The adjacent border and customs area also suffered severe damage."}},"n-rUHFg5":{"type":"image","data":{"image":"r-RIoNzo"}},"n-arqjmm":{"type":"image","data":{"image":"r-j9BNQx"}},"n-iGSrfZ":{"type":"swipe","data":{"contents":{"0":"n-rUHFg5","1":"n-arqjmm"},"caption":"Pre- and post-flood imagery from the upper reaches of Bhote-Koshi river including the town of Timure. Image sources: Vantor Open Data Program (2026), CC BY-NC 4.0 (available here)."}},"n-dycYNz":{"type":"text","data":{"type":"paragraph","text":"Farther downstream, Syabrubesi (28.1633°N, 85.3344°E) experienced extensive damage to houses, hotels, shops, roads, and public infrastructure, while the road link north toward the Nepal–China border was cut. "}},"n-JLw6Bz":{"type":"image","data":{"image":"r-fao3nl"}},"n-7xrdxb":{"type":"image","data":{"image":"r-0ARdUq"}},"n-hRKEo2":{"type":"swipe","data":{"contents":{"0":"n-JLw6Bz","1":"n-7xrdxb"},"caption":"Pre- and post-flood imagery from the upper reaches of Bhote-Koshi river including the town of Syabrubesi. Image sources: Vantor Open Data Program (2026), CC BY-NC 4.0 (available here)."}},"n-XghKLt":{"type":"text","data":{"type":"paragraph","text":"Mailung (28.0718°N, 85.2070°E) and Betrawati (27.9731°N, 85.1860°E) also reported damage to homes, roads, and farmland. "}},"n-B7rDln":{"type":"text","data":{"type":"paragraph","text":"In Nuwakot, the flood devastated settlements along the Trishuli corridor, including Trishuli Bazaar (27.9226°N, 85.1490°E) and Devighat (27.8625°N, 85.1141°E), burying buildings and agricultural land beneath mud and debris and destroying several bridges. Subsequent field reporting described extensive destruction in Trishuli Bazaar, Dhunge Bazaar, and Devighat. Damage to roads and bridges significantly disrupted access to affected communities."}},"n-94prYf":{"type":"text","data":{"type":"paragraph","text":"The flood also damaged the Trishuli and Devighat hydropower stations, contributing to disruptions in electricity generation and distribution. At the nearby 25-MW Nuwakot solar power plant, three generating blocks and the main substation were reportedly swept away or destroyed. The Independent Power Producers’ Association of Nepal (IPPAN) reports 12 hydropower projects were affected by the flood.  Among the missing are nearly 900 workers in these hydropower projects, including students engaged in summer internships. Rescue efforts are still underway at the Upper Trishuli plant and a more detailed breakdown updated on 1 September can be found here . "}},"n-gthusJ":{"type":"text","data":{"type":"paragraph","text":"Farther downstream in Dhading, Baireni Bazaar (approximately 27.800°N, 84.990–84.995°E) experienced comparatively localized inundation and mud deposition. Floodwater entered houses and deposited thick sediment across parts of the market, but current reports do not indicate destruction on the scale documented farther upstream. Residents subsequently began removing mud and recovering belongings from affected homes."}},"n-izR47L":{"type":"text","data":{"type":"paragraph","text":"As of 9:00 NPT on 1 September 2026, the National Disaster Risk and Reduction and Management Authority has reported the death toll has risen to 987, with 3,916 individuals still missing. Additionally, bodies have been recovered downstream including in Chitwan, Newalparasi East and West and as far as in the Uttar Pradesh district of India. These figures remain provisional as search, recovery, and identification efforts continue."}},"n-GkQO2V":{"type":"text","data":{"type":"paragraph","text":"An estimated 4,689 buildings were in the flood-affected zone and a total of 41 bridges have been washed away. "}},"n-efFbz5":{"type":"text","data":{"type":"paragraph","text":"The International Charter “Space and Major Disasters” has been activated to support satellite-based impact mapping. It is still unclear who had warnings about the flood before it arrived, and when – an important question in resilience to future such events.  "}},"n-B2EQrT":{"type":"text","data":{"type":"paragraph","text":"Photos and visual documentation: Aerial and ground photographs of damage along the Bhote Koshi–Trishuli corridor are available in OnlineKhabar’s flood photo gallery. A before-and-after Planet Labs satellite-image comparison is available through this report."}},"n-zExJn9":{"type":"text","data":{"type":"h2","text":"3.0 What caused the flood? "}},"n-GsgnvL":{"type":"text","data":{"type":"paragraph","text":"Initial reports treated a U.S. Geological Survey (USGS) magnitude 4.4 seismic signal near the Nepal–China border as a possible tectonic earthquake and a potential trigger for the flood. However, subsequent USGS analysis reclassified the same signal as a magnitude 5.2 landslide event and they have since determined that the shaking was likely generated by a landslide initiating near 28.271°N  85.515°E. This interpretation is consistent with satellite, video, and field-based evidence suggesting that a massive ice–rock avalanche  occurred above the high-altitude Lhende Khola catchment. "}},"n-zVpw57":{"type":"text","data":{"type":"paragraph","text":"Initially, it was assumed that the initial massive ground failure created debris that temporarily blocked the river to form a lake*, and then released a debris-laden flood downstream. However, more recent seismic analysis of the event as well as detailed reconstruction of flood downstream arrival timing (see above) suggests that damming and release of lake water did not likely contribute significantly to this event because the timing of the initial failure (i.e. the ice-rock avalanche) from seismic records is only seven minutes before the arrival of the flood waters in the nearby community of Gyirong, which is not enough time to have constructed a significant lake in the highland region. Instead, melting of ice and frozen sediment/rock in the initial debris flow and avalanche runout has been attributed to the initiation of the flood. Higher resolution satellite imagery from Planet Labs also shows a large portion of the collapsed region was bedrock with some glacier/ice (see annotated figure).  "}},"n-kqJIS1":{"type":"text","data":{"type":"paragraph","text":"The USGS also observed a second seismic event occurring approximately 3-hours later, which generated energy equivalent to a M4.2 earthquake, but it is not well understood yet how the second seismic source has contributed to the sequence of the avalanche and flood-related events. Details of the collapse and how it initiated the flood are likely to come into sharper view over time as more evidence is assembled."}},"n-gGo72T":{"type":"text","data":{"type":"paragraph","text":"*This hypothesized lake would have been a precursor to the newly formed ones mentioned above that formed substantially after the ice-rock avalanche and are visible today on satellite and drone imagery. "}},"n-9v6AJa":{"type":"image","data":{"image":"r-5BWlOq"}},"n-oJuYVb":{"type":"image","data":{"image":"r-6lYQD0"}},"n-gGb3v1":{"type":"swipe","data":{"contents":{"0":"n-9v6AJa","1":"n-oJuYVb"},"caption":"Images of pre- and post-glacier collapse. Left image is from 25 August 2026 and right image is from 28 August 2025. Both images are annotated with approximate extent of edge of the glacier. Approximate location: 28.292511°N, 85.530220°E. Image sources: Planet Labs PBC with 3.7 meter resolution."}},"n-uPKde7":{"type":"image","data":{"image":"r-LXv6XE","caption":"Annotated source region highlights the collapsed portion in red. Rock is highlighted in gray and glacier ice section in blue. Note these annotations were done using satellite imagery. Approximate location: 28.292511°N, 85.530220°E. Image sources: Planet Labs PBC with 3.7 meter resolution."}},"n-Zny7vp":{"type":"text","data":{"type":"paragraph","text":"Temperature data from nearby climate stations installed by University of Potsdam show the region has been very warm in the past weeks and months. In addition to the high temperatures across the network, station NPA6 (located approximately 20km from the source area, at 85.28567°N, 28.23455°E) shows rapid temperature increases in the morning in the three days prior to the event, which aligns with the timing of failure (8.37AM Nepal time). These quick temperature swings are a key driver for frost cracking and glacial instability. Bodo Bookhagen (Professor at Uni-Potsdam, Germany) notes that these rapid temperature swings are not evident in the other network sites, indicating this was likely a local event. "}},"n-0EO2cg":{"type":"text","data":{"type":"paragraph","text":"This article provides more information about the climate context of this event:  What we can and cannot say about climate change and the Nepal disaster. We expect more work to emerge in coming weeks and months along these lines, given the increasing concern about cryosphere-related disasters in the face of climate change. "}},"n-6O6YAj":{"type":"image","data":{"image":"r-y9MKTo","caption":"Temperature record from TRON station NPA6 (elevation 2500m / 8200ft) located ~20km from the source area. Temperatures in the months preceding the event (indicated with red dashed line) were high, peaking the day before the event at nearly 30°C (86°F). In the three days prior to the event, temperatures peaked in the morning. Figure source: Bodo Bookhagen, University of Potsdam, TRON network. "}},"n-fwj1io":{"type":"image","data":{"image":"r-W8thzm","caption":"Rate of temperature change from TRON station NPA6 (elevation 2500m / 8200ft) located ~20km from the source area. The three days prior to the event show the highest rate of change recorded in the preceding three months, with these rapid fluctuations occurring in the morning hours, the same time as the collapse and subsequent rock-ice avalanche.  Figure source: Bodo Bookhagen, University of Potsdam, TRON"}},"n-lrQnWA":{"type":"text","data":{"type":"h2","text":"4.0 Flood analysis"}},"n-I46Nxw":{"type":"text","data":{"type":"paragraph","text":"By pairing satellite imagery and elevation models with real-time gauge data, CCTV footage, and local reports, we can map out how the flood wave moved downstream and where it hit hardest. Keep in mind that all arrival times, speeds, and damage assessments here are preliminary and will likely be updated as more data comes in. Before and after satellite images can also be used to quantify the inundation of the flood. "}},"n-q28Ahf":{"type":"image","data":{"image":"r-pspeLp","caption":"Flood propagation and impacts on major settlements during the 26 August 2026 Bhote Koshi–Trishuli flood. (a) Flood corridor, estimated arrival times, and preliminary impact classification of major settlements. Colors in (a) and (b) categorically distinguish successive reaches used for reach-scale calculations; they do not encode propagation speed. Settlement impact classifications are based on government situation reports, news coverage, community reports, and available photographs. Panel (a) background imagery: Sentinel-2C, acquired on 12 August 2026. (b) Longitudinal topographic profile along the rock–ice avalanche pathway and downstream channel, together with elevation ranges within ±5 and ±10 km of the mapped river centerline, derived from the Copernicus GLO-90 DSM. Numerical labels show the estimated mean flood-wave propagation speed for each reach. Propagation speeds were estimated from along-channel distances and arrival-time constraints provided by time-stamped CCTV footage, Nepal Department of Hydrology and Meteorology (DHM) river-gauge records, and eyewitness reports; speed ranges reflect uncertainty in arrival times. (c) Relative water-level changes at DHM stations on 26 August. Relative levels are referenced to each station’s first valid 00:00 Nepal Time (NPT) observation and therefore do not represent absolute stage; reported levels also do not account for sediment content in flow. Devghat records a mixed Narayani River signal that cannot be attributed solely to the Trishuli flood. All information here, including arrival times, propagation speeds, and impact classifications, are preliminary and may be revised as additional evidence becomes available."}},"n-UOFlFv":{"type":"text","data":{"type":"paragraph","text":"The flood, travelling at upwards of 164 km/hr (102 miles/hr), reached the town of Timure in approximately 16 minutes from the time of the initial collapse of the glacier and destroyed the upstream Rasuwagadi stream gauge before it could send an emergency warning. The flood destroyed three stream gauges (Rasuwagadi, Syabrubesi, and Phalakhu at Betrawati) and the most upstream stream gauge that remained operational, Galachi, which is located more than 80km downstream, recorded a water height of 8.5 meters (27.9 feet). Further downstream at Devghat, NDRRMA estimated a flood volume of 57.4 million cubic meters, approximately 19.96 million cubic meters above base flow. "}},"n-Kkoijb":{"type":"image","data":{"image":"r-H8qexD","caption":"Mapping of inundated areas due to flooding along the hardest-hit reach of the Trushuli River. Mapped extent of the flood is determined by before and after event Sentinel-2 imagery. Imagery Source: Copernicus Sentinel data 2026, from   Copernicus Data Space Ecosystem."}},"n-JEeFNm":{"type":"text","data":{"type":"paragraph","text":"Using satellite imagery to estimate the extent of inundation in the valley and news reports to estimate the flow velocity, we can estimate the flood discharge (how much water was moving through the channel at any given point) and bed shear stress (how much force was being exerted against the riverbed). These are important characteristics for understanding flood behavior and impact. While the results are still very preliminary estimates, we expect some features to be meaningful. For example,  there is a sharp reduction in channel slope at roughly 10km from the source, which produces a transition in the flood’s behaviour.  In the initial kilometers along the Lhende Khola and upper Bhote Kosi River, above Timure, the flood is in an extremely erosive, high-energy regime, capable of mobilizing massive boulders and stripping bedrock. The flood then transitions to a lower-energy regime dominated by downstream sediment transport and deposition. Delineating this energy transition makes it possible to constrain where the flood accumulated and evacuated the greatest volume of debris, as well as the transport distances over which this material continued to drive bank destabilization, channel bed incision, and widespread sediment deposition downstream."}},"n-ElLW9a":{"type":"image","data":{"caption":"Channel Geometry, Flood Discharge, Slope, and Boundary Shear Stress Derived from the 8-m NASA HMA DEM. This calculations required several notable assumptions. First, the inundation area was mapped by identifying the largest cross-sectional extent of flood debris visible on satellite images and was then discretized into perpendicular segments along the length of the channel spaced 100 m apart. For each segment, volumetric discharge was calculated by multiplying the cross-sectional channel area below the segment (determined from the 8-m NASA HMA DEM) by the speed of the flow (determined from the timing of flood arrival in towns reported in various online media; see above). Where available, upper and lower estimates of flow velocity were used to bound the discharge estimate. We assume a hyperconcentrated flow regime for the entire length of the flood originating from the confluence of the glacial valley with the Lhende Khola, which appears to mark the transition between debris avalanche and flood. We note that this may not be a valid assumption for the river section upstream of Timure, where the debris concentration was likely higher due to the proximity to the ice/rock avalanche.\n(a) Elevation Profile: raw minimum bed elevation (min(Z)) along the river bed measured every 100 meters from the NASA HMA 8 m DEM (2017 imagery). A rolling 5-node minimum is applied to track the lower boundary envelope and bypass artificial DEM void spikes. A Savitzky-Golay filter then smooths the profile to provide a continuous topographic baseline (2 km smoothing). (b) Cross-Sectional flow Area (m2) across the middle line of the surface flood extent measured at 100 m intervals. (c) Discharge Volumetric discharge (Q=A×V) mapped across speed segments. It computes minimum and maximum discharge bounds rendered as a shaded uncertainty band using the range of velocity estimates for each river segment, along with a mean discharge profile expressed in Sverdrups (1 Sv=106 m3/s). (d) Channel slope (S=∣dz/dx∣). (e) Bed shear stress using τ=ρgHS, where ρ=1500 kg/m3 (hyperconcentrated flow density) for maximum shear stress (τmax using maximum depth Hmax =WSE−Zmin ) and mean shear stress (τmean using hydraulic mean depth Hmean =A/Top Width), converted to kPa.","image":"r-LF5vAJ"}},"n-sbHqOe":{"type":"text","data":{"type":"h2","text":"5.0 Seismic and other geophysical records"}},"n-9uDpv8":{"type":"text","data":{"type":"paragraph","text":"Seismometers provide unique information about landslides and major floods in remote regions by providing precise locations and timing of processes which happen quickly enough that satellites do not observe them directly. Several researchers have been producing and sharing seismic records from this event, which are helping fill in the gaps of our understanding of the cause of this event from satellite images. "}},"n-pPodyB":{"type":"text","data":{"type":"paragraph","text":"Large mass movements like ice/rock avalanches and massive debris floods can generate seismic signals comparable in size to moderate earthquakes on faults. For example, in July 2025, a landslide in Taiwan recorded a  M4.9 signal and formed a landslide-dammed lake on the Matai’an River. Similarly, in August 2025, a landslide in Tracy Arm, Alaska registered as a  M5.4 seismic event and generated a local tsunami in the fjord. The August 2026 Trishuli Nepal event fits this same pattern. "}},"n-A0TGD5":{"type":"text","data":{"type":"paragraph","text":"EarthScope, the US NSF National Geophysical Facility, has posted information about both near- and far-field records from the Trishuli event. "}},"n-bVdXBV":{"type":"text","data":{"type":"paragraph","text":"The KKN station, located on the edge of the Kathmandu Valley, is providing some of the most widely reported seismic records. An example including the hours before the event is shown from Marianne Karplus (UT El Paso) below:"}},"n-eu3TGY":{"type":"image","data":{"image":"r-eNn6yv","caption":"Seismic signals recorded at Kakani Station (KKN) of the National Earthquake Monitoring and Research Centre (NEMRC) in Nepal, ~15 km northwest of Kathmandu (latitude 27.8, longitude 85.279, elevation: 2042 m) and ~60 km from the location of the landslide and glacial collapse near Langtang Lirung peak. Top panel shows the unfiltered signal starting Aug. 26, 2026 at 08:37:10 NPT (“zero time” of landslide and glacial collapse) for 300 seconds. Middle panel shows the signal for 24 hours before and 6 hours after the landslide. Note there may be precursory seismic activity recorded in the hours before the landslide and glacial collapse. Bottom panel shows the seismic spectrogram, filtered from 0.005-25 Hz for 24 hours before and 6 hours after landslide. "}},"n-0vloYG":{"type":"text","data":{"type":"paragraph","text":"Other records are emerging from additional instruments, including Raspberry Shake seismometers, many of which are deployed in schools through the Seismology-at-School program in Nepal. One of these records, processed by EarthScope engineer Christopher Calvelage, is shown below (right) along with the KKN record."}},"n-khfMGW":{"type":"image","data":{"image":"r-vLy0Dp","caption":"Examples of seismic records emerging from this event. The KKN station (left) is ~58 km from the location of the landslide that initiated the flood, and about 20 km from the river channel. The AM.R3B1E (Raspberry Shake) is ~50 km from the landslide but ~40 km from the river. "}},"n-96lMbf":{"type":"text","data":{"type":"paragraph","text":"These seismic records also show that there were small precursory events prior to the main collapse. Using data from KKN and a handful of Raspberry Shake instruments near Kathmandu, Christopher Calvelage has shown that events start as isolated detections a couple of days apart approximately 12 days before the main collapse and increase about 4 hours before the moment of failure. Interestingly, repeaters are visible for up to 12 days before the main landslide, suggesting repeated slip along the failure plane."}},"n-DBrtau":{"type":"image","data":{"image":"r-GoNkQb","caption":"To look for events that might have preceded the landslide, we choose four small events leading up to the collapse that were used as templates for a template matching workflow. We search for detections from August 1st-26th on stations NK.KKN, IO.EVN, and a handful of Raspberry Shake instruments near Kathmandu. (a) shows the full detections history, with an increase in events in the days prior to the event. Filled in purple dots have higher correlation with the templates (large, taller unfilled circles), and small unfilled circles have a lower correlation. Bottom panel shows the number of detections per hour. Shaded purple region is shown in panel b. (b) final 7 hours before the collapse, highlighting the increase in small events prior to collapse. Bottom panel shows the number of detections per 15 minutes. Note: due to the limited available data locating the precursor events is not possible and thus not every detection is a true precursor to the collapse. Figure source: Christopher Calvelage, Earthscope. "}},"n-unGw6M":{"type":"text","data":{"type":"paragraph","text":"Using the regional and global seismic stations, it is also possible to estimate the volume and mass of the landslide. Using the regional stations only, the volume is estimated to be between 284 - 492 million cubic meters, and using the global teleseismic stations results in an estimated volume of 197-349 million cubic meters – that is equivalent to approximately 100,000 - 200,000 olympic swimming pools worth of material that collapsed. This is within a similar range of the findings out of DPRI in Kyoto. If these preliminary estimates are correct, this would be the largest rock-ice avalanche ever recorded. To put this into context, the 2021 Chamoli rock-ice avalanche displaced 27 million cubic meters. Researchers are still working to understand what these records are telling us about how this event happened - though we expect estimates like this to be revised in the coming days and beyond. Look back here in the coming days for more updates."}},"n-uruD8I":{"type":"image","data":{"image":"r-IDpEU0","caption":"By inverting long period signals at both more regional stations and stations at teleseismic distances (panel a) using Green’s functions from two Earth models to get a range of estimates, it is possible to estimate the mass volume of the landslide. This yields a complex force history function (panel b) with a maximum force ranging from 1.1 - 2 x 1012 N. We then convert the maximum force to volume via the empirical relationships from Ekstöm & Stark, 2013 and Chao et al., 2016. Assuming a bulk density of 2200 kg/m3, the regional and teleseismic solutions give 284-492 and 197-349 Mm3 respectively (panel c). Figure source: Christopher Calvelage, Earthscope. "}},"n-BA88wg":{"type":"text","data":{"type":"h2","text":"6.0 Recent similar events and the rapidly changing landscapes of the Himalaya"}},"n-VNnuXt":{"type":"text","data":{"type":"paragraph","text":"High-mountain “water towers” are rapidly changing landscapes. Warming is accelerating glaciers mass loss and permafrost thaw, while shifts from snow to rain and more erratic precipitation are altering runoff patterns and destabilizing rock and ice slopes. The past decade has seen multiple events like this, at unprecedented and frightening frequency."}},"n-7bxxoc":{"type":"text","data":{"type":"paragraph","text":"A previous flood in 2025 on the Trushuli River was initiated by a different mechanism than happened last week. In that earlier event, sudden release of water from a glacial dam (i.e. a glacial lake outburst flood or GLOF) was the cause of the flood. "}},"n-g2ltPa":{"type":"text","data":{"type":"paragraph","text":"Five years ago, another devastating event which is closely comparable occurred in a neighboring river basin (the Melamchi and Indrawati Rivers), where a destructive, sediment-laden flood struck and caused severe damage to settlements, roads, bridges, and important infrastructure, including the Melamchi Water Supply Project that would deliver fresh water to Kathmandu. However the cause of the Melamchi Flood was not related to a glacial collapse. This event showcases that such extreme floods can start with a combination of monsoon rainfall, rain-on-snow, and lake breach. The erosion volume by this event is up to 75 million cubic meters, leaving the river corridor downstream choked by sediment by meters. As in the present, the impacts extended beyond the initial flood wave through sediment remobilization."}},"n-YlLIkL":{"type":"text","data":{"type":"paragraph","text":" The 2021 Chamoli disaster in the Indian Himalaya, where a massive rock-ice avalanche generated a destructive flood and wiped out downstream infrastructure, illustrates how sudden a cryospheric slope failure can initiate a devastating hazard cascade. Combining climatic and hydrologic forcings can also create erosive, sediment-charged floods. "}},"n-Jzs36K":{"type":"text","data":{"type":"paragraph","text":"In detail, each event has had different triggers - but they have shared in common their devastating consequences, as well as their origin at the high elevations of the Himalaya where change is happening especially rapidly. These extreme floods threaten the growing population in mountain communities. Road building, hydropower development, tourism, and settlement expansion place more people and assets in narrow, hazard-prone valleys; demographic growth and land-use change can therefore amplify losses."}},"n-f11QTd":{"type":"image","data":{"caption":"Recent major floods in the Himalayas color coded by their initiation cause and sized based on the number of deaths and missing persons. The current estimates of missing and casualties from the 2026 Trishuli flood (as of 18 September 2026) marks this as one of the deadliest Himalayan floods on record.","image":"r-BIq7z8"}},"n-wifAll":{"type":"text","data":{"type":"h2","text":"7.0 Paleo-flood events in the Trishuli"}},"n-E86Dbq":{"type":"text","data":{"type":"paragraph","text":"While this Bhote Koshi - Trishuli flood was devastating, the affected valley preserves a record of past, catastrophically large flood events. Large, rounded boulders line the Trishuli valley and other high Himalaya-draining rivers are the legacy of past extreme flood events. In the Trishuli and adjacent Sun Koshi valley, fluvially transported boulders exceeding 5 m in diameter are common. The lithology of most of these boulders does not match the local geology, but rather rock units that outcrop tens of kilometers upstream. In a 2020 study, Huber and others determined boulder-emplacement timing and estimated paleo-flood magnitudes based on boulder size. They show that most boulders in the Trishuli and Sunkoshi were last mobilized and came to rest about 5000 years ago in flood events that far exceed typical monsoon discharges by one to two orders of magnitude. Images and videos from this Trishuli flood suggest this was a larger event, moving larger boulders than the flood event that impacted the valley ~5000 years ago (please note it has not been confirmed these are boulder but also have the possibility of being large, dirty chunks of ice). "}},"n-XQoz2q":{"type":"text","data":{"type":"paragraph","text":"Put another way, this 2026 Trishuli flood is the largest flood event to impact the Trishuli valley in 5000 years. Huber and others suggest that drying in the regional climate of the Himalaya between 5 and 4 thousand years ago, during the Early Holocene Climate Optimum, may have affected glacier dynamics, resulting in catastrophic flooding of both the Trishuli and Sun Koshi valleys. This interpretation has clear parallels with the 2026 Trishuli flood in the context of today's warming climate. "}},"n-34uJnI":{"type":"image","data":{"image":"r-Vc6ui2","caption":"Images of boulders within and lining the Trishuli Valley and paleo-flood estimates compared to historical discharge records from nearby stream gaging stations (Huber et al., 2020)."}},"n-0xDlGZ":{"type":"text","data":{"type":"h2","text":"8.0 What others are seeing"}},"n-CkYrXB":{"type":"text","data":{"type":"paragraph","text":"This is not an exhaustive list but is an attempt to pull together rapid scientific analyses of this event (we are trying to keep this updated with relevant links or additional material). Please contact us at contact@geoclash.org if you would like us to link to your analyses here."}},"n-4oQCyb":{"type":"text","data":{"type":"bullet-list","text":"

  • Hydraulic models of the flood in the headwaters:

    • "}},"n-Ti8496":{"type":"text","data":{"type":"paragraph","text":"Note that these infer travel times of the flood pulse similar to those described in Section 2 above"}},"n-nfB37m":{"type":"text","data":{"type":"bullet-list","text":"
  • The climate change context:  What we can and cannot say about climate change and the Nepal disaster 
  • Kinematic flood wave reconstruction and inundation analysis: Bhote Koshi Flood 2026: A Reconstruction from Open Satellite Data
  • 3D numerical model of the flood from Johan Guame, ETH Zurich, SLF Davos: https://www.instagram.com/reels/Dc-YyUmNS_h/
  • Guo et al., (Accepted) Progressive entertainment transformed a high-elevation ice-roc avalanche in Nepal into the 26 August debris flow in Gyirong, Xizang. https://www.sciengine.com/doi/10.1360/CSB-2026-1255.
  • Parajuli, Nawaraj. Khatiwada, Durga. 26 August 2026. Scientific Investigation of the 26 August 2026 Rasuwa Ice–Rock Avalanche and Subsequent Flash Flood in the Nepal–China Transboundary Himalaya using Satellite Imagery, DEM Analysis, Seismic Evidence and Geospatial Methods. https://www.parajulinawaraj.com.np/HGR/events/rasuwa-2026/index.html
    • "}},"n-Ok3RQP":{"type":"text","data":{"type":"bullet-list","text":"

  • Wang, T., Sassa, S., Yang, W. et al. 2026. Precursor of a powerful large glacier landslide causing tsunami floods in the 26 August 2026 Nepal disaster. Landslides. https://doi.org/10.1007/s10346-026-02842-6.

    • "}},"n-KvkEwK":{"type":"text","data":{"type":"bullet-list","text":"

  • Numerical simulation of the avalanche from Antoine Lucas, IPGP: https://www.linkedin.com/in/antoine-lucas-b66ab613/

    • "}},"n-DN0GBR":{"type":"text","data":{"type":"h2","text":"9.0 Call for action/preparations"}},"n-ZMVxyL":{"type":"text","data":{"type":"paragraph","text":"Nepal Finance Minister Swarnim Wagle has estimated total reconstruction costs between $4 billion and $5 billion."}},"n-RrJbuY":{"type":"text","data":{"type":"bullet-list","text":"
  • Fundraising: https://pmdrf.nchl.com.np/
  • Mapping effort: https://tasks.hotosm.org/explore?campaign=2026+Nepal+Floods&omitMapResults=1
    • "}},"n-7NfUjr":{"type":"text","data":{"type":"paragraph","text":"Coordinates are approximate settlement-center locations in WGS84, compiled from GeoNames and OpenStreetMap place records. They should not be interpreted as flood-impact boundaries."}},"n-NuiSIY":{"type":"text","data":{"type":"h2","text":"10.0 Related Links"}},"n-h8nV7L":{"type":"text","data":{"type":"numbered-list","text":"
  • ICIMOD. “Major flash flood sweeps through Nepal’s Rasuwa District.” August 26, 2026.
  • International Charter Space and Major Disasters. “Flood Sin Nepal—Activation 1052.” August 26, 2026.
  • The Kathmandu Post. “Nepal flash flood leaves extensive destruction along the Bhotekoshi–Trishuli corridor.” Updated August 26, 2026.
  • OnlineKhabar English. “Which towns and settlements were worst affected by the Rasuwa flood?.” August 26, 2026.
  • Nepal Police. “Rasuwa flood: 95 deaths so far.” August 26, 2026; updated 7:14 PM NPT.
  • The Kathmandu Post. “Update: Rasuwa flood death toll climbs to 95 as dozens remain missing.” Updated August 26, 2026, 9:05 PM NPT.
  • OnlineKhabar English. “In pictures: Rasuwa flood leaves trail of destruction from Rasuwagadhi to Bidur.” August 26, 2026.
  • Hindustan Times. “Satellite images show Nepal before and after devastating flash floods.” August 26, 2026.
  • Associated Press. “At least 160 killed and hundreds missing after flash floods in Nepal and China.” August 26, 2026.
  • USGS. “M 5.2 Landslide - 55 km NW of Kodǎri, Nepal” Accessed August 26, 2026.
  • Shugar, D. “LinkedIn post: The cause of the horrific floods in Nepal.” August 26, 2026.
  • The Kathmandu Post. “Ice avalanche, debris lake may have triggered Bhotekoshi flood.” August 26, 2026.
  • OnlineKhabar English. “What caused the Rasuwa flood? Experts point to possible glacial lake outburst.” August 26, 2026. 
  • https://nirajbhusal.github.io/rasuwa-flood-bulletin/?lang=en
    • "}},"n-tb9oo8":{"type":"text","data":{"type":"h2","text":"More from CLaSH"}},"n-Iz8JDI":{"type":"text","data":{"text":"Interested in learning more about CLaSH's rapid response activities, please check out our events page for details on our rapid response work.","type":"paragraph"}},"n-QQoSe3":{"type":"button","data":{"text":"CLaSH rapid response activities","link":"","alignment":"center"}},"n-yeYDMy":{"type":"text","data":{"text":"","type":"h2"}},"n-5VWsnv":{"type":"text","data":{"text":"This research was supported by the Center for Land Surface Hazards (CLaSH), funded via National Science Foundation Cooperative Agreement NSF-2425607.","type":"paragraph"}},"n-1Fjvv1":{"type":"attribution","data":{"content":"https://www.geoclash.org","attribution":"contact@geoclash.org"}},"n-CZOBLs":{"type":"credits","children":["n-yeYDMy","n-5VWsnv","n-1Fjvv1"]},"n-XfjsAU":{"type":"story","data":{"storyTheme":"r-Sb19Id"},"config":{"coverDate":"first-published","isSocialIconsHidden":false,"shouldHideSimilarItems":true,"scriptEmbedDomains":[],"isScriptEmbedEnabled":false,"storyLocale":"en"},"children":["n-SK506m","n-5k34sW","n-SU5rux","n-CSUaLF","n-bKYNPE","n-xOKjG5","n-kgAVNL","n-IZ9WXf","n-xpCNqr","n-OyU2xB","n-RW3LIq","n-lTFomU","n-0kNQvv","n-nUovyG","n-4pB0i7","n-6BHAhV","n-X1oyyo","n-s4OQ1H","n-G4oO8B","n-I0jGyd","n-gTV6Ge","n-DhlFgf","n-iGSrfZ","n-dycYNz","n-hRKEo2","n-XghKLt","n-B7rDln","n-94prYf","n-gthusJ","n-izR47L","n-GkQO2V","n-efFbz5","n-B2EQrT","n-zExJn9","n-GsgnvL","n-zVpw57","n-kqJIS1","n-gGo72T","n-gGb3v1","n-uPKde7","n-Zny7vp","n-0EO2cg","n-6O6YAj","n-fwj1io","n-lrQnWA","n-I46Nxw","n-q28Ahf","n-UOFlFv","n-Kkoijb","n-JEeFNm","n-ElLW9a","n-sbHqOe","n-9uDpv8","n-pPodyB","n-A0TGD5","n-bVdXBV","n-eu3TGY","n-0vloYG","n-khfMGW","n-96lMbf","n-DBrtau","n-unGw6M","n-uruD8I","n-BA88wg","n-VNnuXt","n-7bxxoc","n-g2ltPa","n-YlLIkL","n-Jzs36K","n-f11QTd","n-wifAll","n-E86Dbq","n-XQoz2q","n-34uJnI","n-0xDlGZ","n-CkYrXB","n-4oQCyb","n-Ti8496","n-nfB37m","n-Ok3RQP","n-KvkEwK","n-DN0GBR","n-ZMVxyL","n-RrJbuY","n-7NfUjr","n-NuiSIY","n-h8nV7L","n-tb9oo8","n-Iz8JDI","n-QQoSe3","n-CZOBLs"]}},"resources":{"r-UYZKYR":{"type":"image","data":{"resourceId":"679fab49-e994-4a76-bc6b-a42713f7625a.jpeg","provider":"item-resource","height":1950,"width":2600}},"r-lHD1hM":{"type":"image","data":{"resourceId":"75f62a49-30ad-4c1b-bb1b-b93634d7bb04.jpeg","provider":"item-resource","height":5000,"width":3388}},"r-PfURI5":{"type":"image","data":{"resourceId":"sTRQhmWGTnfp1_uO8k0_G.jpg","provider":"item-resource","height":3100,"width":4384}},"r-8J9m7q":{"type":"video","data":{"resourceId":"CPKx_KEF1Kokq2xsgOAxo.mp4","provider":"item-resource"}},"r-PMycKU":{"type":"image","data":{"resourceId":"1YO9O4avdJMXeWQm8xjDU.jpeg","provider":"item-resource","height":720,"width":1280}},"r-RIoNzo":{"type":"image","data":{"resourceId":"cde938e6-d20c-448a-a861-d352fb2d2480.jpeg","provider":"item-resource","height":2480,"width":3507}},"r-j9BNQx":{"type":"image","data":{"resourceId":"Fu1In2bsfnAY__WO5okuU.png","provider":"item-resource","height":2480,"width":3507}},"r-fao3nl":{"type":"image","data":{"resourceId":"f4d0fcb9-c053-48c8-8101-e1091f8fbb11.jpeg","provider":"item-resource","height":2480,"width":3507}},"r-0ARdUq":{"type":"image","data":{"resourceId":"9bac2152-731e-4705-ab1d-aa043300e8c8.jpeg","provider":"item-resource","height":2480,"width":3507}},"r-5BWlOq":{"type":"image","data":{"resourceId":"18cd7e62-3716-446a-9c6e-6a08274c3f01.jpeg","provider":"item-resource","height":3100,"width":4383}},"r-6lYQD0":{"type":"image","data":{"resourceId":"ce363079-48b4-4412-9911-293204a40573.jpeg","provider":"item-resource","height":3100,"width":4383}},"r-LXv6XE":{"type":"image","data":{"resourceId":"TZZ4kQr7MtRlDE0aAwlJT.jpg","provider":"item-resource","height":4929,"width":4929}},"r-y9MKTo":{"type":"image","data":{"resourceId":"C9Yq0JF-27ZsTFsOFUVzW.png","provider":"item-resource","height":2700,"width":4200}},"r-W8thzm":{"type":"image","data":{"resourceId":"EEy-TLLxvd_0LxZcxx6gB.png","provider":"item-resource","height":2700,"width":4200}},"r-pspeLp":{"type":"image","data":{"resourceId":"0d287415-a971-4eb9-a6f3-861e11e4cdc8.jpeg","provider":"item-resource","height":5000,"width":3358}},"r-H8qexD":{"type":"image","data":{"resourceId":"tiFYL_LFENjwqLDd-lSJW.png","provider":"item-resource","height":970,"width":1643}},"r-LF5vAJ":{"type":"image","data":{"resourceId":"7d8aeb4e-db35-4048-8d51-4e1ed829d172.jpeg","provider":"item-resource","height":5000,"width":4362}},"r-eNn6yv":{"type":"image","data":{"resourceId":"QQpFngI_OKwPPJHDry6V4.jpg","provider":"item-resource","height":1006,"width":1728}},"r-vLy0Dp":{"type":"image","data":{"resourceId":"doLGN377fIlPvnjkgLSuq.png","provider":"item-resource","height":1869,"width":2975}},"r-GoNkQb":{"type":"image","data":{"resourceId":"RvuzkL2x7XBNplIdCnVsy.png","provider":"item-resource","height":1152,"width":1311}},"r-IDpEU0":{"type":"image","data":{"resourceId":"bZNlxxE4mjiJpYSJUdC45.png","provider":"item-resource","height":650,"width":1854}},"r-BIq7z8":{"type":"image","data":{"resourceId":"iQ4A_yygg9qkYwgxjO37u.jpg","provider":"item-resource","height":1351,"width":2401}},"r-Vc6ui2":{"type":"image","data":{"resourceId":"d2NGSY_rJ8NkUawkYFFFs.png","provider":"item-resource","height":2400,"width":3000}},"r-Sb19Id":{"type":"story-theme","data":{"themeId":"summit","themeBaseVariableOverrides":{},"themeItemId":"b09f8c5713454a2b9ada9af9bb3efa29"}}}}