Mount St. Helens remains the Cascades’ most likely volcano to erupt again

Of every volcano in the contiguous United States, the USGS says Mount St. Helens is the one most likely to erupt again, a ranking that has held since the mountain blew apart its own summit on May 18, 1980. The debris avalanche that morning stripped 400 meters, or roughly 1,300 feet, off the peak in a matter of minutes and left behind a horseshoe-shaped crater 2 by 3.5 kilometers across, now partly filled by a lava dome and a small glacier. As of September 16, 2025, the volcano’s official status sits at Green, or NORMAL, the calmest of the USGS alert levels.

Calm status is not the same as low priority. Mount St. Helens still carries the agency’s Very High Threat rating, and its history explains why federal monitoring in the Cascades looks the way it does today. Few American landscapes changed as fast, or as visibly, as the one around this mountain did in a single May morning, and the scientific response to that morning still shapes how every other Cascade volcano gets watched.

The morning the summit came off

A magnitude 5.1 earthquake at 8:32 a.m. triggered what the USGS’s account of the 1980 eruption calls the largest debris avalanche on Earth in recorded history, roughly 2.5 cubic kilometers of rock and ice that raced up to 23 kilometers down the North Fork Toutle River valley. A lateral blast followed within moments, flattening forest across 600 square kilometers and accelerating outward at more than 480 kilometers, or 300 miles, per hour. The eruption column that rose afterward reached more than 24 kilometers, or 80,000 feet, into the sky in under 15 minutes.

Ash from that column drifted east, plunging Spokane into darkness roughly 400 kilometers away and reaching the Great Plains more than 1,500 kilometers from the volcano; within 15 days, the plume had circled the entire planet. A USGS retrospective on the eruption’s scientific impact puts the human toll at 57 deaths, including David Johnston, a USGS volcanologist who was monitoring the mountain from a ridge nearly six miles away when the blast overran his position.

A crater still settling three decades later

Erosion has kept reshaping what the eruption left behind. A 1982 survey measured the volcano’s new maximum elevation at 2,549.7 meters, or 8,365 feet, but a 2009 lidar survey found it had dropped further, to 2,539 meters, or 8,330 feet, which the USGS attributes to continued erosion and the collapse of loose rock along the crater’s rim. A lava dome built during eruptive episodes in the 1980s, and again between 2004 and 2008, now occupies part of the crater floor alongside a glacier that has grown in the shaded, ice-friendly conditions the collapse created. Scientists still track the dome’s shape and the glacier’s slow advance as part of routine monitoring, since a renewed dome-building episode is one of the more plausible next chapters for a volcano that has already produced one this century.

Why Johnston’s death rebuilt the monitoring system

Johnston’s death became a turning point rather than only a tragedy. The USGS says the eruption exposed sharp divisions that had existed “before 1980” among scientists studying volcano hazards, monitoring, and basic volcanology, divisions the agency worked deliberately to close in the years afterward. The Cascades Volcano Observatory grew directly out of that response, eventually building a mobile-deployment program, the Volcano Disaster Assistance Program, that has since assisted with more than two dozen volcanic crises worldwide since 1986.

Congress folded that lesson into law decades later, authorizing the National Volcano Early Warning System in March 2019 to formally coordinate monitoring across every hazardous volcano in the country, with Mount St. Helens still treated as the proving ground for techniques later applied elsewhere. High-precision GPS receivers and satellite radar imaging have since replaced the tiltmeters and hand-surveyed benchmarks that were the best instruments available to Johnston’s colleagues in 1980, letting today’s scientists detect ground swelling of a few centimeters rather than waiting for visible bulging on the flank.

What keeps the “most likely” label attached

Mount St. Helens earns its ranking partly through recent behavior most Cascade volcanoes cannot match: a catastrophic eruption in 1980, a dome-building phase from 2004 to 2008, and the densest seismic network of any volcano in the range, built specifically because of that track record. The Cascades Volcano Observatory, which describes its mission as helping people “live knowledgeably and safely with volcanoes in Washington, Oregon, and Idaho,” keeps that network running continuously rather than only after signs of unrest appear.

The broader Very High Threat category Mount St. Helens shares with 17 other U.S. volcanoes comes from the same national ranking system a 2018 USGS assessment updated, one built to direct monitoring resources rather than to forecast a date. Green status today means no signal of unrest in current data, not a change to the underlying likelihood, which is exactly the distinction the ranking was designed to preserve.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.