Scientists have mapped disaster danger zones across Alaska and Washington state, warning that collapsing mountainsides could unleash tsunamis and mudflows similar to Nepal's recent tragedy.
Researchers monitoring unstable slopes in the United States say thawing frozen ground and retreating glaciers leave coastal areas and river valleys vulnerable to sudden rockslides and volcanic debris flows.
Wednesday's deadly flash flood in Nepal was likely triggered when an enormous chunk of glacier broke away and plunged thousands of feet into the valley below, according to an initial scientific assessment.
More than 360 people have died and more than 1,400 remain missing across Nepal and Tibet following Wednesday's disaster. The United States Geological Survey identified a glacier collapse and debris flow that produced a seismic signal initially mistaken for an earthquake.
In Nepal's Nuwakot district, muddy flood waters overwhelmed a town located along the confluence of the Trishuli and Tadi rivers. Scientists noted that the disaster illustrates a hazard cascade, where a single mountain collapse sets off widespread destruction far downstream.
Marten Geertsema, an adjunct professor of earth sciences at Simon Fraser University in Canada, warned that similar mechanisms threaten parts of North America. "Alaska has much of the same ingredients for hazard cascades that occur in Nepal and surrounding countries," Geertsema told the Daily Mail.
Geertsema explained that thawing frozen ground can weaken mountainsides over time, while retreating glaciers remove the ice masses that previously supported steep rock slopes.
Alaska Landslide and Tsunami Risk
In Alaska, retreating glaciers bring deep seawater closer to unstable mountainsides, allowing falling rock to unleash powerful waves into coastal inlets. Geertsema noted that rock slides plunging into deep water bodies can generate extremely high localized tsunamis.
Geertsema and 13 other scientists warned in 2020 that an unstable slope at Barry Arm, located in Alaska's Prince William Sound about 30 miles northeast of Whittier, could collapse into the water and trigger a catastrophic tsunami. At the time, researchers considered a landslide-generated tsunami likely within 20 years.
Alaska's latest monitoring update reports no signs of large-scale active movement at Barry Arm, although experts note that smaller failures could still trigger localized tsunamis. Geertsema added that despite improvements in monitoring technology, events such as landslide tsunamis remain frustratingly difficult to predict.
Historical Alaska Tsunami Events
Scientists point to several historical incidents in Alaska to demonstrate the destructive power of landslide-generated waves. At Taan Fiord in October 2015, a landslide sent water surging 633 feet up nearby slopes, stripping forest from eight square miles of land, though no injuries were reported.
Earlier, at Lituya Bay in July 1958, an earthquake triggered a rockslide that forced water 1,720 feet up a mountain ridge. The resulting tsunami destroyed a cabin and a lighthouse, killing two people aboard a fishing boat.
More recently, at Tracy Arm on August 10, 2025, another mountainside collapse sent water surging nearly 1,600 feet up the opposite slope, stripping vegetation from the inlet walls without causing any fatalities.
Mount Rainier Volcanic Mudflows
In Washington state, researchers monitor a different type of threat at Mount Rainier, an active, heavily glaciated stratovolcano located roughly 60 miles from Seattle. Looming over more than 3.3 million people in the Seattle-Tacoma metropolitan area, Rainier features slopes heavily covered in glaciers and unstable volcanic rock.
Experts say these conditions create the ideal setup for volcanic mudflows known as lahars. These powerful mixtures of water, rock, mud, and debris resemble churning wet concrete as they rush downstream, and some can begin even without a volcanic eruption.
More than 90,000 people are estimated to live within mapped danger zones for Mount Rainier lahars. Computer models suggest a large mudflow could reach residential areas outside Mount Rainier National Park within 15 to 60 minutes of starting, depending on the location.
Scientists warn that three Washington towns could be devastated within minutes if a massive volcanic mudflow suddenly roars down Mount Rainier during an eruption. A mudflow could strike Orting before continuing downstream toward Sumner and Puyallup, or travel south toward Ashford and areas near Alder Lake.
Lahar Warnings and Historical Impacts
The United States Geological Survey has previously stated that Mount Rainier is not due for an eruption and we do not see any signs of a potential eruption at this time. However, the agency cautioned that devastating lahars can occur without warning, citing the Electron Mudflow of 1500 AD caused by a massive landslide on the volcano's western flank.
Recent studies of Rainier's western flank warn that the area remains vulnerable to a future large-scale collapse that could send mudslides rushing down multiple river paths. To mitigate the risk, the USGS established a lahar detection and warning system on Mount Rainier in 1998.
The warning network relies on buried ground sensors and tripwires along key river valleys to detect vibrations from approaching mudflows and automatically alert emergency operations centers. Between 2015 and 2021, officials upgraded the system with 14 modern stations that transmit real-time data, cover additional river drainages, and use advanced seismometers and cameras to spot lahars earlier.
Despite these technological upgrades, scientists acknowledge that destruction from a fast-moving lahar could occur too quickly for residents to react in time. The deadliest modern lahar in the United States occurred during the 1980 eruption of Mount St. Helens, when a collapsing north flank and pyroclastic flows rapidly melted glacial ice.
That torrent surged more than 60 miles through the Toutle and Cowlitz river valleys, destroying over 200 homes, 195 miles of roads, and 27 bridges. Today, the hazard in Washington is considered so severe that emergency officials regularly conduct massive evacuation drills to prepare residents for a disaster many experts believe is inevitable.
