Mount St. Helens, a prominent Pacific Northwest volcano, became iconic after its powerful 1980 eruption. Despite dramatic changes to its summit, the volcano remains a closely watched dynamic entity.
Mt. St. Helens’ Geological Activity
Mount St. Helens is a conical stratovolcano, part of the Cascade Volcanic Arc in the western United States. The formation and activity of these volcanoes are directly linked to a geological process called subduction.
Subduction occurs where the denser Juan de Fuca oceanic plate slides beneath the lighter North American continental plate. As it descends, it heats and melts, forming magma. This magma then rises towards the surface, feeding the volcanoes of the Cascade Arc. Mount St. Helens has been the most active volcano in the Cascade Range over the past 10,000 years, with its modern cone developing over the last 2,200 years. Its eruptive history has included both effusive lava flows and highly explosive eruptions.
How Volcanoes Are Monitored
Scientists employ various methods to monitor active volcanoes like Mount St. Helens. These tools provide data that help volcanologists understand the volcano’s internal state and identify changes that may signal unrest. One primary method involves using seismometers, which detect earthquakes. Magma movement beneath a volcano often triggers swarms of earthquakes, and changes in their frequency, intensity, and depth can indicate rising magma.
Ground deformation is another key indicator, measured by GPS and tiltmeters. These measurements can reveal swelling of the volcano as magma accumulates beneath the surface. Volcanic gas emissions are also closely monitored using sensors that analyze the composition and concentration of gases like sulfur dioxide and carbon dioxide. An increase in certain gases can suggest that magma is nearing the surface. Additionally, remote sensing techniques, such as satellite imagery, thermal cameras, and infrasound sensors, detect changes in heat flow or low-frequency sound waves.
Assessing Future Eruption Risk
Based on its geological history and ongoing monitoring data, Mount St. Helens will erupt again. The United States Geological Survey (USGS) identifies it as the Cascade volcano most likely to erupt within our lifetimes. Scientists interpret patterns in monitoring data to assess the potential for an eruption, looking for increased seismicity, ground swelling, and changes in gas emissions. For example, an increase in shallow earthquakes, coupled with ground swelling, often points to magma moving closer to the surface.
While these monitoring techniques provide valuable insights, predicting the exact timing or nature of future eruptions remains challenging. Volcanic systems are complex, and even with advanced tools, precise short-term predictions are difficult. Mount St. Helens has experienced periods of elevated seismic activity that have continued for years without leading to an eruption. Scientists can identify periods of heightened unrest, allowing for warnings and preparations, but the precise moment of eruption often remains uncertain until very close to the event.