No, Mount St. Helens isn’t erupting again. It’s just stirring up leftover ash 45 years after ‘the big one’

Strong easterly gusts swept across Mount St. Helens and nearby slopes in the southern Washington Cascades, kicking up old deposits of ash from its historic 1980 eruption. (USGS via CNN Newsource)

For a moment, it seemed like a blast from the past: a plume over Mount St. Helens on Tuesday looked like the volcano might be erupting again. But fortunately, this was not an eruption — just a wind-whipped encore decades in the making.

According to the U.S. Geological Survey (USGS), strong easterly gusts swept across the crater and nearby slopes in the southern Washington Cascades, kicking up old deposits of ash from its historic 1980 eruption, often referred to as the “big one,” and flinging them thousands of feet into the air.

The agency emphasized this is “not a sign of renewed volcanic activity.” Both the volcano alert level and the aviation colour code remain at green, the lowest setting, and activity “remains at normal, background levels.”

Images shared by the USGS and the National Weather Service in Portland showed plumes of ash drifting downwind, fueling momentary panic for anyone watching the skies. The ash was also visible on satellite and the NWS said pilot reports indicated ash had risen up to 10,000 feet (3,048 metres) in the air.

Resuspended volcanic ash isn’t unusual at Mount St. Helens. The massive 1980 eruption blasted a column of ash and gas more than 15 miles into the atmosphere and triggered a devastating landslide, killing 57 people in what was the most destructive eruption in modern U.S. history.

Pockets of that fine, powdery rock still linger today on the volcano’s flanks and inside the crater. When conditions line up — dry surfaces, no snow cover and strong winds — the deposits can be lofted again.

That’s exactly what happened Tuesday when a stubborn ridge of high pressure over the Pacific Northwest not only brought record September temperatures to Washington and Oregon, where large parts are experiencing a severe drought, but also set off dry, gusty east winds barreling across Mount St. Helens.

The impacts of resuspended volcanic ash are often not hazardous, but visibility can dip, air quality can suffer and aircraft engines can ingest volcanic grit. “There have been no significant changes in hazards at Mount St. Helens as a result of this activity,” the USGS said. Luckily, the plume should fade once winds die down.

By CNN Meteorologist Briana Waxman