Mount St. Helens Volcanic Ash Triggers Aviation Warnings

A dangerous cloud of volcanic ash was detected billowing from Mount St. Helens, prompting urgent aviation warnings. A SIGMET, a serious aviation weather alert, was issued late Thursday and extended into Friday as satellite imagery and webcams captured a plume of ash drifting northwest of the Washington State volcano.

The volcanic ash cloud rose as high as 12,000 feet above sea level, posing a potential hazard to aircraft. Images from the U.S. Geological Survey's (USGS) webcams monitoring the volcano showed plumes of ash engulfing the formation, creating the impression of renewed activity.

However, officials stressed that powerful winds associated with a high-pressure weather system over the Pacific Northwest had swept up old volcanic ash from the ground. These winds, blowing across the Cascade Mountains, stirred up decades-old ash from Mount St. Helens, sending it thousands of feet into the atmosphere. "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 USGS stated. "No eruption is in progress, and Mount St. Helens remains at Aviation Color Code Green and Volcano Alert Level Normal."

The Cascades Volcano Observatory issued an official aviation notice at 1:01 p.m. local time Thursday after webcam footage showed ash reaching an estimated 12,000 feet above sea level. A separate SIGMET warning was in effect from 7:37 p.m. until 11:36 p.m., alerting pilots to hazardous ash in the skies near the volcano.

Volcanic ash is particularly dangerous to aircraft as it consists of tiny, jagged fragments of rock and volcanic glass. If ingested into a jet engine, these 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.

Mount St. Helens experienced a major eruption on May 18, 1980, which sent a plume of ash 2.5 miles into the sky. That eruption resulted in 57 fatalities and the destruction of more than 200 homes, earning it the moniker America's deadliest volcano. The 1980 eruption's ashfall caused widespread disruption, with highways closed for weeks and over 1,000 flights canceled.

While the current ash event is not indicative of a new eruption, the volcano has shown signs of increased activity. In June 2024, scientists detected 350 earthquakes over five months, most of which were less than magnitude 1.0. The largest quake felt at the volcano was a magnitude 2.0 on May 31, 2024. In 2025, the number of recorded earthquakes per week peaked at 38 events, occurring approximately 4.6 miles below the crater floor.

Specialized equipment has detected magma flowing through chambers deep underground, causing the volcano to recharge. A surge in quakes was also recorded in 2023. Experts at the Cascades Volcano Observatory noted that short-term increases in earthquake rates are common at Mount St. Helens and are considered part of background seismicity. The periods of elevated seismicity in 2023 and 2024 represent the largest short-term increase in earthquake rates since the last eruption ended in 2008.

Similar sequences of quakes occurred between 1988-1992, 1995-1996, and 1997-1999 without triggering an eruption. These quakes were thought to be caused by the pressurization of the magma transport system, triggered by the arrival of additional magma. Recharge events occur when magma enters a reservoir around 2.5 to six miles below sea level.

"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, the USGS noted that small earthquakes were recorded at the site just before the deadly 1980 eruption.