At least 95 people are dead and 54 Americans are among the 579 reported missing after a devastating flash flood and landslide in Nepal, a disaster that experts warn could be replicated at any time by Washington state's Mount Rainier.
The natural disaster on Wednesday is believed to have been triggered by an avalanche or glacier collapse that sent a chunk of ice roughly 2,000 feet wide falling thousands of feet into the Lhende Khola river valley along the border between Nepal and Tibet.
The massive ice shard mixed with water, rock and debris to create a sudden and powerful surge of muddy floodwater that rushed into the Bhote Koshi River and devastated the Rasuwa district of Nepal.
Surveillance cameras from the scene of the disaster captured the moment when waves taller than local buildings swept through the streets, decimating structures and washing away crowds of people who were caught outdoors.
Pacific Northwest lahar risk
Scientists say the events in Nepal serve as a grim warning for the Pacific Northwest, where experts fear a similar massive disaster could take place at any time.
Mount Rainier, considered one of America's most dangerous volcanoes, is an active, heavily glaciated stratovolcano looming over more than 3.3 million people. It threatens cities such as Seattle, Tacoma and Yakima in Washington, as well as Portland, Oregon.
More than 60,000 residents live within the volcano's lahar danger zone. Lahars are fast moving rivers of water, rock, mud and debris that behave like wet concrete and bulldoze everything in their path within 15 minutes.
Crucially, these deadly torrents can occur with or without a volcanic eruption. Scientists have warned that landslides, heavy rainfall, melting glaciers or even small earthquakes could destabilize part of Mount Rainier, unleashing a deadly cascade through the surrounding river valley.
US Geological Survey warnings
The US Geological Survey has named the volcano one of its highest priorities in terms of threat potential, despite Mount Rainier not producing a significant eruption in more than 1,000 years.
"The volcano is not 'due' for an eruption and we do not see any signs of a potential eruption at this time," the USGS has previously said. Scientists have found no signs of a volcanic eruption taking place, though a recent false alarm at the volcano appeared as strange tremors for 72 hours.
However, the agency noted that a devastating lahar could arrive without warning. They cite the Electron Mudflow of 1500 AD, which was caused by a landslide on the west flank of the volcano.
Studies of the west flank have warned that this area remains vulnerable to a future large scale collapse that would send mudslides down multiple river paths.
Communities in the path
The resulting mudflow could hit communities such as Orting, before continuing toward Sumner and Puyallup. It could also travel south toward the town of Ashford and areas near Alder Lake.
Computer models from the USGS showed the mudflow would reach homes and visitor areas inside Mount Rainier National Park in about five minutes, and reach towns outside the park in as little as 15 to 60 minutes.
The USGS set up a lahar detection and warning system on Mount Rainier in 1998. The system uses sensors buried in the ground and tripwires along key river valleys that sense the vibrations of an approaching lahar and automatically alert emergency centers.
The agency upgraded the system between 2015 and 2021 with 14 new modern stations to transmit data in real time, cover additional river drainage areas, and use better technology such as seismometers and cameras to spot lahars earlier. Still, the resulting devastation could come too fast for residents to react in time.
Evacuation drills
The danger of lahars in Washington has become so alarming that emergency officials now conduct massive evacuation drills designed to prepare residents for a disaster many experts believe is inevitable.
On April 23, more than 45,000 students and staff from over 20 schools participated in one of the world's largest lahar evacuation exercises, practicing evacuations to higher ground while emergency officials tested warning systems.
"It is necessary to be aware of the natural warning signs of an approaching lahar: ground rumbling accompanied by a roaring sound like a jet or locomotive," the USGS warned in a statement.
The most critical piece of advice officials give is to move to higher ground as soon as a siren sounds or the signs of a lahar are felt. This could mean abandoning cars and running on foot in areas where roads and highways become blocked with traffic.
The deadliest modern lahar in the United States struck during the 1980 eruption of Washington's Mount St Helens, when the collapsing north flank of the volcano and scorching pyroclastic flows rapidly melted glacial ice.
The resulting torrents of mud and debris surged more than 60 miles through the Toutle and Cowlitz river valleys, destroying 27 bridges, more than 200 homes and 195 miles of roads. That disaster contributed to a total death toll of 57 people.
Similar devastation was seen internationally when a village on the Indonesian island of Java was inundated by a lahar following the eruption of the Semeru volcano in 2022.
