On the clear, rainless morning of August 26, the Bhotekoshi-Trishuli Flood swept downstream from the Lhende Khola (also known as Bhotekoshi and Donglin Tsangpo in Tibet) near Nepal-China border, rushed through the Trishuli River and ultimately reached the Narayani (Gandaki) River at Devghat. The disaster, which has also been termed the Himalayan Tsunami, began when a rock-ice block from a glacier at Langtang Lirung broke off and fell vertically around 1800 m on to the Lhende Khola1, 3. The floods claimed over 1,500 lives and left over 6,500 injured. More than 5,500 people are still missing.
Flood zone and its source area (Source: Chand et al. 20263)
While the primary disaster subsided by the evening, secondary hazards have increased further risks throughout the Gandaki River Watershed. The deluge has reduced the stability of the toes of slopes resulting in secondary landslides in the flood-affected zone. Since further disasters in the Narayani (Gandaki Basin) can further damage the major highways, monitoring of the whole basin is of utmost concern.
The disaster has questioned the way we monitor our Himalayan region. Previously, the major focus was on slowly retreating glaciers and increasing glacier lakes, but monitoring permafrost loss, discontinuities, and possible structural failures of the bedrocks should also be prioritized. Also, the fact that scientific community and policy makers could not apply the lessons learnt from the 2012 Seti Gandaki Flood, 2021 Chamoli (Uttarakhand) disaster, and the 2025 Blatten (Switzerland) Glacier Collapse stands out as one of the greatest tragedies.
Bhotekoshi-Trishuli Disaster, 2026
Bhotekoshi-Trishuli Disaster, 2026
What we know till date
Pre-Event Phase
August 14 – August 25, 2026 (12 days prior)
Seismic Precursors
EarthScope and regional seismic networks (including the Kakani (KKN) station in Nuwakot, and local school-based Raspberry Shake networks) detect small, isolated precursory seismic events1. Scientists recognize “repeating” signals suggesting a gradual slip along the failure plane of the Langtang-Lirung massif.
August 23–25 (3 days prior)
Temparature Records
Temperature records from Potsdam’s TRON station NPA6 (~20 km from the source area) show rapid morning warming cycles, which act as a key driver of frost cracking and cryospheric slope instability1.
August 25 (1 day prior)
Peak Temperature Records
High-altitude temperatures peak at nearly 30°C (86°F) at station NPA6, compounding weeks of intense warming, permafrost degradation, and glacier mass loss1.
Beginning of the Catastrophe: The Avalanche (August 26, 2026)
04:37 AM
Sharp Increase in Seismic Precursors
A sharp increase in small seismic precursor detections begins, escalating dramatically in the final four hours leading to the collapse.
08:20 AM
Minor Seismic Record
A minor seismic precursor is recorded near the Rasuwagadhi border area, later calculated as equivalent to a magnitude 2.6 tectonic event2.
08:37 AM
The Failure
A colossal rock-ice avalanche breaks off between 5,200m and 3,800m asl on the northern side of the Langtang Lirung massif. The collapse zone (~2.26 km²) and adjacent eroded area (~2.93 km²) mobilize an estimated 142 million m³ of material3. Regional and teleseismic wave analysis puts the total collapsed volume even higher—estimating between 197 and 492 million m³. DMG registers the massive ground failure as a magnitude 4.4 ML (Richter scale) seismic event2. The USGS also originally reports it as tectonic M4.4 earthquake, but later corrects it as a magnitude 5.2 landslide-generated seismic event1.
08:40 AM
Debris reaches the Lhende River
The high-speed debris flow strikes the Lhende River at 2,900m asl, initiating a downstream flood wave and briefly blocking the river with snow, ice, and rock3.
One kilometer downstream from the Gyirong (Kerung) border, the Rasuwagadhi stream gauge records a final water level of 1.62 meters before sending any warning2. The station had the warning level of 6 m and danger level of 7 meters. The flood velocity at this point has been calculated to be over 180 km/hr.
Flood Propagation and Downstream Impact
08:44 AM (7 mins post-collapse)
@Gyirong (Kerung)
The flood wave arrives at the Tibetan side of the Gyirong (Kerung) customs.1
08:50 AM (13 mins post-collapse)
@Syabrubesi (9 km downstream from Gyirong border)
The surge reaches Syabrubesi, where the river-gauge records a water level rise to 3.8 meters (warning level: 5.5 meters) before the station is swept away.
09:20 AM
@Betrawati (36 km downstream from Gyirong border)
The Betrawati river-gauge records a water level rise to 3.55 m before it is swept away.
Department of Hydrology and Meteorology (DHM) activates its emergency alert system and broadcasts 632,295 to 679,295 SMS warning messages to downstream residents along the corridor.
09:30 – 09:50 AM
@Trishuli Bazaar and Bidur
The wave passes Trishuli Bazaar and Bidur, depositing meters of mud and thick sediment across the valley, burying agricultural land, and destroyinh multiple bridges1.
10:00 – 10:10 AM
@Belkot and Devighat
The flood wave reaches the Tadi River at Belkot and sweeps away Devighat1. Tadi records a rapid water level peak of +2.53 m at 10:10 AM.
10:20 – 10:50 AM
@Galchhi
The deluge reaches Galchhi.1
The Prime Minister convenes an emergency meeting of the National Disaster Risk Council, deploying drone teams and ordering evacuations across 15 downstream municipalities3.
At 10:50 AM, Galchhi records an extreme water level peak of +8.50 meters (representing a rise of ~9 meters in just 30 minutes)1.
11:20 – 11:45 AM
@Malekhu
At 11:20 AM, the surge reaches Furke (Malekhu), crossing its local warning threshold of 7 meters2.
At 11:40 AM, the Furke Khola Station (Malekhu) crosses its extreme danger threshold of 8 meters. Peaking at 10.48 meters2, the Furke Khola bridge is swept away, and the flood is confirmed approaching Mugling3.
01:00 PM
@Mugling
The flood wave passes Mugling, moving downstream toward the Narayani River confluence.
02:14 PM
@Kalikhola
Kalikhola (near Mugling) crosses its danger threshold of 12.1 meters, peaking at 12.35 meters.
Peak, Stabilization, and Aftermath
02:30 PM – 6:00 PM
@Devghat
At 02:30 PM to 02:40 PM, the first waves of flood reach Devghat Hydrological Station.1
At 04:00 PM, the flood peaks at Devghat at 6.57 m, with a peak discharge of 5,850 m3/s.3
The total flood volume passing Devghat is estimated at 57.4 million m³ (including 19.66 million m³ of excess water above seasonal base flow)1.
06:30 PM
The Whole Watershed
The flood begins to subside. Devghat water levels return to ~4 m as search-and-rescue (SAR) operations continue into the night3.
Secondary Hazards in the Gandaki Watershed
August 28
A New Warning
Satellite and drone imagery provided by China reveal that two new debris-dammed lakes have formed near the source area. One major lake (770m along its major axis) formed by a secondary landslide blocks the Lhende Khola river bank, and another (530m axis) sits directly below the collapsed glacier. By the morning of August 28, the Lhende Khola lake begins to overflow naturally, neutralizing the immediate risk of an outburst1.
August 28 – 30
One Landslide-dammed lake drains out
The lake formed from damming of the Lhende Khola begins draining out on August 29. It completely drains out by August 30.
The lake below the glacier needs further monitoring.
August 30
Landslide at Krishna Bhir
The Trishuli undercuts the toe of the Krishna Bhir, an old landslide that had previously been stabilized through water draining and biotechnical methods. The landslide occurs in the Prithvi Highway, severing connection of the Terai with Kathmandu.
August 31
Landslide at Syar Khola
At about 9:30 AM, a landslide occurs on the upstream of the Syar Khola, a tributary of the Budhi Gandaki River. It blocks the Khola and forms a lake. The lake drains out by the evening.
September 8
Landslide at Kimrung Khola, Kaski
At about 06:00 PM, a landslide partly blocks the Kimrung Khola in the Modi Khola Catchment. Modi Khola is a tributary of the Seti Gandaki River.
Chand, M. B., Kayastha, R. B., Adhikari, S., Pokharel, A., Moktan, B., Bajracharya, H., Basnet, U., Paudel, P. K., (2026). Rapid situation report: Bhotekoshi–Trishuli catastrophe. Youth Alliance for Environment (YAE), Kathmandu, Nepal.
Feature image: Reported Hazard Zones and Hydrological Stations along the Bhotekoshi–Trishuli–Narayani Rive Corridor in NDRRMA (2026). Rapid Damage and Needs Assessment (RDNA): Rasuwa-Bhotekoshi Flood 2026. https://ndrrma.gov.np/np/study-report/416
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