Monitoring a volcano requires scientists to use of a variety of techniques that can hear and see activity inside a volcano. The USGS Volcano Hazards Program monitors volcanoes to detect signs of change that forewarn of volcanic reawakening. To fully understand a volcano's behavior, monitoring should include several types of observations (earthquakes, ground movement, volcanic gas, rock chemistry, water chemistry, remote satellite analysis) on a continuous or near-real-time basis.
Scientists collect data from the instrument networks then analyze them to look for out-of-the-ordinary signals. By comparing the data analysis with similar results from past volcanic events, volcanologists are better able to forecast changes in volcanic activity and determine whether and when a volcano might erupt in the future. Most data can be accessed from our offices in the observatories but visits to the volcanoes, when possible, add valuable information.
Rapid advances in technology are helping scientists develop efficient and accurate monitoring equipment. These new systems are capable of collecting and transmitting accurate real-time data from the volcano back to Observatory offices, which improves eruption forecasting. It is important that instruments be installed during quiet times when volcanoes are not active so that they are ready to detect the slightest bit of volcanic stirring. Early detection gives the maximum amount of time for people to prepare for an eruption.
When a volcano begins showing new or unusual signs of activity, monitoring data help answer critical questions necessary for assessing and then communicating timely information about volcanic hazards. For example, prior to the 2004 eruption at Mount St. Helens monitoring equipment recorded a large increase in earthquake activity. Scientists quickly examined other monitoring data including gas, ground deformation, and satellite imagery to assess if magma or fluid was moving towards the surface. Based on the history of the volcano and the analysis of the monitoring data scientists were able to determine the types of magma could be moving towards the surface. This type of knowledge helps scientists figure out the possible types of volcanic activity and the associated hazards to people. Knowing the hazards helps officials determine which real-time warnings are needed to prevent loss of life and property.