America’s Deadliest Volcano Sparks Alerts as Ash Fills Skies

A dangerous cloud of volcanic ash rising from Mount St Helens has prompted urgent aviation warnings.

A SIGMET, or significant meteorological alert for aviation, was issued late Thursday and remained in effect into early Friday after satellite images and webcams showed an ash plume drifting northwest from the Washington State volcano, south of Seattle.

The ash climbed to around 12,000 feet above sea level, creating a potential risk for aircraft operating in the region.

The warning initially sparked concern that volcanic activity could be returning at the site of one of the deadliest eruptions in US history.

Webcam images from the US Geological Survey (USGS) showed clouds of ash surrounding the volcano, giving the appearance that Mount St Helens had suddenly become active again.

Officials later clarified that strong winds had lifted old ash from the ground rather than an eruption producing fresh material.

Mount St Helens erupted catastrophically on May 18, 1980, sending an ash plume 2.5 miles into the atmosphere.

The disaster killed 57 people and destroyed more than 200 homes, cementing the volcano’s reputation as America’s deadliest.

A high-pressure weather system over the Pacific Northwest generated powerful winds across the Cascade Mountains. Those winds stirred decades-old ash on Mount St Helens and carried it thousands of feet into the air.

“This phenomenon is not the result of recent volcanic activity and occurs during times of high winds and dry, snow-free conditions in the Mount St Helens region,” the agency said.

“No eruption is in progress, and Mount St Helens remains at Aviation Color Code Green and Volcano Alert Level Normal.”

It added that resuspended volcanic ash should be treated as hazardous because it can damage aircraft and pose risks to human health.

The Cascades Volcano Observatory issued an aviation notice at 1.01pm local time Thursday after webcam footage indicated that the ash had reached an estimated 12,000 feet above sea level and was moving northwest.

A revised volcanic ash advisory followed at 5.48pm.

A separate SIGMET was active from 7.37pm until 11.36pm, warning pilots about hazardous ash in the airspace around Mount St Helens.

While no eruption was taking place, specialists cautioned that the airborne ash could still endanger aircraft and affect human health.

Volcanic ash is especially hazardous because it is made up of tiny, sharp-edged particles of rock and volcanic glass, unlike the soft residue left by a typical fire.

If sucked into a jet engine, the abrasive particles can cause serious damage and, in extreme circumstances, lead to a complete loss of engine power.

The particles can also irritate the eyes and lungs, reduce visibility and damage machinery, according to the USGS.

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While the USGS assured the public that Mount St Helens is not erupting, the volcano gave the nation a scare in June 2024 when it began rumbling.

Scientists detected 350 earthquakes over five months. Most of these – more than 95 percent – have been less than magnitude 1.0 and are too small to be felt at the surface.

The largest quake felt at the volcano, located in southwestern Washington, about 50 miles northeast of Portland, Oregon, was a magnitude 2.0 on May 31, 2024.

There are fears the earthquakes could lead to another massive explosion reminiscent of the 1980s eruption.

In 2025, the number of earthquakes recorded per week reached a peak of 38 events per week, mostly happening around 4.6 miles below the crater floor.

Specialized equipment has detected that magma has been flowing through chambers deep underground, causing the volcano to recharge. A surge in quakes was also recorded in 2023.

‘Short-term increases in earthquake rates are common at Mount St Helens and are considered part of background seismicity,’ experts at the Cascades Volcano Observatory said in a statement.

‘The last two periods of elevated seismicity (in 2023 and 2024) represent the largest short-term increase in earthquake rates since the last eruption ended in 2008.’

However, similar sequences involving even more quakes broke out in 1988 to 1992, 1995 to 1996, and 1997 to 1999. None of these directly triggered an eruption.

The quakes were thought to be caused by pressurization of the magma transport system, which in turn was triggered by the arrival of additional magma, a process called recharge.

Magma gradually bubbles through the lower crust and builds up in a reservoir around 2.5 to six miles below sea level. ‘Recharge’ events break out when magma enters this reservoir, causing quakes.

‘There have been no significant changes in other monitoring parameters (ground deformation, volcanic gas or thermal emissions) and no change in hazards at Mount St. Helens as a result of this activity,’ the Observatory concluded.

However, in 1980, small earthquakes were recorded at the site just before the deadly eruption.

The volcano exploded sideways and sent an enormous landslide of a super-heated mix of ash, rock fragments and gas flowing downslope. 

The ash and gas then rose, blocking the sun, turning the sky completely dark.

Destructive mudflows, also known as lahars, swept up homes and trucks as officials closed bridges and stalled railroad track operations.

Most of the debris from the seismic event turned westward, down the North Fork Toutle River and formed a mound of deposit.

The total avalanche volume equaled a measurement of one million Olympic-sized swimming pools.

Trees were also blown to the ground or scorched by the brutally hot lava, leaving the once-dense forest virtually empty.

The volcanic ash fell like snow throughout Washington, Idaho and western Montana. Officials had to close highways for weeks and airlines canceled more than 1,000 flights.

In the days following the devastation, an estimated 540 million tons of ash drifted up from the structure and settled over a total of seven states.