Mount St. Helens, located in the Cascade Range of Washington State, experienced a catastrophic eruption on May 18, 1980, which drastically reshaped the mountain’s profile. The volcano remains geologically young and highly active, making the question of when it will erupt again a constant subject of scientific inquiry and public concern. Understanding the volcano’s current status and the methods used by scientists to track its behavior offers insight into its future potential.
The Current State of the Volcano
Mount St. Helens is not currently erupting, but it is far from dormant, remaining an active part of the Cascade Volcanic Arc. The U.S. Geological Survey (USGS) and the Cascades Volcano Observatory (CVO) continuously monitor the mountain, maintaining its alert level at “Normal.” Scientists detect small, low-magnitude earthquakes occurring a few kilometers beneath the crater floor, which are considered part of the normal background seismicity. These events are associated with magma recharge, where new magma enters the plumbing system deep below the surface, keeping the volcanic system “live.”
The CVO uses a network of instruments to track the volcano:
- Seismometers
- GPS receivers
- Gas sensors
Currently, there are no significant changes in ground deformation, which would indicate swelling or bulging of the mountain, and volcanic gas emissions are barely detectable. While short-term increases in earthquake rates are common, they have historically occurred without leading to an eruption, such as sequences observed in the late 1980s and 1990s.
Forecasting the Next Eruption
The exact day or year of the next Mount St. Helens eruption cannot be predicted decades in advance, but long-term forecasting relies on understanding the volcano’s history and probability. Geological evidence shows that Mount St. Helens is the most active volcano in the Cascade Range and has a very high probability of renewed eruptive activity in the future. The volcano has had two eruptive episodes in the past three decades, including the 2004–2008 dome-building phase, which supports the expectation of future events.
The official view from the USGS is that the volcano is the most likely in the Cascades to erupt again in our lifetimes, but the next event will probably not be as catastrophic as the 1980 blast. The deep, horseshoe-shaped crater created in 1980 makes a similar large debris avalanche and lateral blast less likely now. Instead, the most probable future events will resemble the dome-building eruptions of 1980 to 1986 and 2004 to 2008, where viscous lava slowly extruded to form a dome inside the crater.
The long-term geological record indicates that the volcano typically alternates between periods of repose and periods of frequent, smaller eruptions. This high frequency of past activity suggests the possibility of renewed activity in the coming decades.
Precursors and Immediate Warning Signs
When Mount St. Helens does begin to prepare for a new eruption, scientists expect to observe a clear sequence of precursors that would provide days to weeks of warning. The most important initial sign would be a rapid increase in seismic activity, specifically an earthquake swarm, as rising magma fractures the surrounding rock. These earthquakes would become more frequent and potentially more energetic than the current background activity.
Another significant warning sign is ground deformation, which is the physical swelling or bulging of the volcano’s surface. This is measured using GPS receivers and tiltmeters, which can detect subtle changes in slope or elevation as magma or gas pressures increase beneath the surface.
Changes in the volume or composition of volcanic gases emitted from the crater would also be an indicator. An increase in gases like sulfur dioxide (\(\text{SO}_2\)) or carbon dioxide (\(\text{CO}_2\)) suggests that magma is rising closer to the surface. These measurable changes in seismicity, ground shape, and gas output would allow the USGS to issue a short-term forecast and warnings, enabling public safety measures and evacuations to be enacted.