CVO dismantles Mount St. Helens’ VALT seismic station after 18 years in service.
Crater Glacier’s mass of rock and ice getting a little too close to this Mount St. Helens monitoring station.
While VALT will be missed for sentimental reasons, plans are underway to install a replacement on the crater floor away from the reach of Crater Glacier. No gaps in monitoring are anticipated.
VALT: The early days
The volcano monitoring station formerly known as VALT was installed in 2006 on Mount St. Helens’ crater floor. It was called VALT because a vault-like structure about the size of a large doghouse was built into the rocky deposits to protect the state-of-the-art (at that time) broadband seismometer from environmental variables such as temperature and humidity.
VALT joined a network of 13 permanent stations operating within 12 miles (20 km) of Mount St. Helens. The network collected seismic data during the 2004-08 lava-dome-building eruption that included rockfall, lahars (volcanic mudflows) and snow avalanches, plus bursts of more than 500 events, tremor-like signals, long-period (low-frequency) earthquakes, and regular, localized, small-amplitude drumbeat earthquakes, as semisolid magma spines pushed toward the surface.
Crater Glacier advances toward VALT
During the 2004-08 eruption, the emerging lava spines split Crater Glacier in two, shoving the ice up against the enclosing crater walls. This caused the separate arms of ice to surge around the east and west sides of the lava domes, moving as much as 4.5 feet per day. The arms merged in the spring of 2008 to completely encircle the lava domes. After the eruption ended, the glacier’s wide terminus continued to advance northward across the crater floor a rate of about 1 foot per day, headed toward VALT.
VALT: Crater Glacier looming
After the eruption ended in 2008, VALT remained, collecting data as seismicity at Mount St. Helens returned to pre-eruption levels. Over the next 16 years, it withstood snow, ice, rain, wind, and baking heat, detecting rockfalls, earthquakes, and the steady advance of Crater Glacier. As the distance between Crater Glacier and VALT decreased, it was clear a demobilization plan was needed. Anxious about damage to the station from the advancing glacier and hazards to people working at the site, a CVO field team dismantled VALT on June 6, 2024.
VALT II coming soon
Plans are underway to install a replacement on the crater floor away from the reach of Crater Glacier. No gaps in monitoring are anticipated.
The seismic network at Mount St. Helens now includes over 20 permanent stations, a network that is much more robust than that when VALT was installed. Technology has advanced to where a vault-like structure isn’t required, and seismometers today are buried in the ground. Broadband technology is still state-of-the-art, providing scientists with intricate data about what’s happening beneath this active volcano.
View Mount St. Helens station locations and data from the Pacific Northwest Seismic Network and learn more about Mount St. Helens’ eruptive history.
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