Chapter 13 Volcanism
In 2005 USGS geologist Chris Newhall made a list of the six most important signs of an imminent volcanic eruption. They are as follows:
- Gas leaks — the release of gases (mostly H2O, CO2, and SO2) from the magma into the atmosphere through cracks in the overlying rock
- Bit of a bulge — the deformation of part of the volcano, indicating that a magma chamber at depth is swelling or becoming more pressurized
- Getting shaky — many (hundreds to thousands) of small earthquakes, indicating that magma is on the move. The quakes may be the result of the magma forcing the surrounding rocks to crack, or a harmonic vibration that is evidence of magmatic fluids moving underground.
- Dropping fast — a sudden decrease in the rate of seismicity, which may indicate that magma has stalled, which could mean that something is about to give way
- Big bump — a pronounced bulge on the side of the volcano (like the one at Mount St. Helens in 1980), which may indicate that magma has moved close to surface
- Blowing off steam — steam eruptions (a.k.a. phreatic eruptions) that happen when magma near the surface heats groundwater to the boiling point. The water eventually explodes, sending fragments of the overlying rock far into the air.
With these signs in mind, we can make a list of the equipment we should have and the actions we can take to monitor a volcano and predict when it might erupt.
Assessing Seismicity
The simplest and cheapest way to monitor a volcano is with seismometers. The University of Utah Seismograph Stations (UUSS) operates the Yellowstone Seismic Network, and earthquake data are transferred from Yellowstone to the UUSS in real time using a radio and satellite telemetry system. UUSS scientists analyze the earthquake data and report information out via their website.
The United State Geological Survey operates 5 volcano observatories in the U.S., and monitors volcanic activity worldwide. Volcano monitoring and research conducted at five U.S. volcano observatories advances our understanding of active volcanism and its impacts, and enables the USGS Volcano Hazards Program to provide information about and warnings of volcanic activity in the United States. Each observatory is assigned a geographic area of responsibility and issues formal notices of activity for volcanoes in those regions. The observatories and their partner organizations operate real-time volcano monitoring networks, disseminate forecasts and notifications of significant activity, assess volcano hazards, conduct scientific research into volcanic processes, and work with communities to prepare for volcanic eruptions. The seismic networks operated by the USGS (and partners) allow geologists to determine the exact location and depth of the seismic activity so that they can see where the magma is moving.
Detecting Gases
Water vapor quickly turns into clouds of liquid water droplets and is relatively easy to detect just by looking, but CO2 and SO2 are not as obvious. It’