Disaster Management Options for Volcano Hazards

Introduction: The Challenge of Volcanic Forecasting

Currently, there are many options for forecasting volcanic natural disasters such as eruptions and explosions. None of the current methods are accurate enough to predict a volcanic event every time or quickly enough to allow for the evacuation of nearby populations. This is problematic given that so many volcanic areas are densely populated. These include the Alban Hills south of Rome, Italy; the "Ring of Fire" in the Cascade Mountains of the northwestern United States; and the Tungurahua volcano in Ecuador (Choi, 2004; Kerr, 2003). To make matters worse, few volcanoes around the world are well monitored—or monitored at all (Mileti, 1999).

While current methods are not perfect, they offer detection in many cases. If they are implemented and better understood, new developments may emerge that can more reliably predict volcanic events and save the lives of those living near such natural hazards.

Mileti (1999) suggests that there are two main factors in volcanic disaster warning and prediction: "forecasting explosive events and assessing volcanic hazard" (p. 185). Methods to detect whether a volcanic hazard exists are generally more accurate than methods that attempt to predict an explosive event (Kerr, 2003; Mileti, 1999). Assessing a volcanic hazard simply means determining whether a volcano is still active and should be monitored for possible future activity. This assessment is more difficult with volcanoes that have large caldera systems and that do not erupt frequently (Kerr, 2003; Mileti, 1999). Predicting where and when an explosive eruption event will occur is considerably harder. Yet, knowing when and how a volcano will erupt is the most important issue in volcanic forecasting because it has the potential to save lives. Most current forecasting methods look for confirmation that fresh magma—liquid rock—has traveled into chambers in the upper crust, approximately three to six miles below the earth's surface (Kerr, 2003).

Seismic and Electromagnetic Monitoring

Seismic monitoring is one of the most common ways to track volcanic activity (Choi, 2004; Mileti, 1999). Seismometers monitor earth movement, including the earthquakes and tremors that sometimes indicate volcanic activity such as underground magma movement (Choi, 2004). Though seismic activity is often successfully linked to volcanic events, not all seismic events indicate a coming eruption (Kerr, 2003). For this reason, seismometer readings do not always provide accurate predictions (Choi, 2004).

Seismic tomography is a related method that uses tremor activity and seismic waves to "image" the underground workings of a volcano. Because seismic waves travel at different speeds through magma than through solid rock, recording an earthquake from several different monitoring stations in the same area can illuminate where volcanic magma chambers are located. This information, in turn, can help predict where eruptions might occur (Kerr, 2003).

Electromagnetic monitoring can also be used in conjunction with seismic monitoring and tomography. By using strainmeters buried deep in the earth around a volcano, a "long-period seismic event" (LP) can be detected and monitored (Kerr, 2003). This monitoring approach allows scientists to make better predictions for volcanoes that are regularly active.

Ground Deformation and Geochemical Monitoring

Ground deformation monitoring uses satellite and aerial images, as well as topographic data, to assess whether the area around a volcano is bulging or swelling from built-up magma and gases (Kerr, 2003). Magma and gases accumulating just below the surface before an eruption can cause a bulge many miles in diameter. Because these swells are so large, they cannot be detected by the naked eye (Kerr, 2003). Satellite-borne radars alert volcanologists when such bulges appear. The satellites monitor global positioning system (GPS) devices on the ground, using triangulation to determine whether the surface is deforming. However, the absence of a bulge does not rule out an impending eruption, so this method is only useful in certain cases and where a volcano is already well-monitored (Kerr, 2003).

Geochemical monitoring involves observing changes in gases associated with volcanic movement. Watching inactive volcanoes for gas emissions can serve as a precursor to eruption (Choi, 2004). Sulfur dioxide, carbon dioxide, and other gases escaping from the earth signal the movement of magma underground, sometimes indicating that an eruption is imminent (Choi, 2004; Kerr, 2003). The instrumentation used to monitor escaping gases is not ideal, however; it is both unwieldy and fragile, making it ill-suited for field monitoring outside of laboratory conditions (Choi, 2004). Additionally, Kerr (2003) notes that gas observation can be misleading, since both increases and decreases in gaseous activity can signal a coming eruption.

References

Choi, C. (2004). Volcanic sniffing. Scientific American, 291(5), 22–24.

Kerr, R. A. (2003). High-tech fingers on Earth's erratic pulse. Science, 299(5615), 2016–2019.

Mileti, D. S. (1999). A reassessment of natural hazards in the United States. Washington, D.C.: National Academies Press.