Advances in science and monitoring techniques have meant that scientists have made great advances in forecasting eruptions. A number of different techniques are used to monitor changes in physical processes which may indicate increasing volcanic activity. However, due to the availability of expertise, cash and technology, only 20% of volcanoes are currently monitored, most of which are in MEDCs.
Prediction / Monitoring Techniques:
Remote Sensing
Landsat images which show the amount of energy from the sun being reflected from the earth's surface when an image is taken by a satellite, can be used to indicate environmental change and can be used to identify areas affected by an eruption. This can then be used for future hazard mapping.
Other satellite imagery can be used to predict volcanic eruptions. Infra-red images of volcanoes can be made every 15 minutes by geo-stationary satellites allowing thermal mapping to be used to detect hot spots where magma is rising to the surface, enabling a warning to be given. In 1998, the eruption of Pacya in Guatemala was detected a week before it happened by a satellite using infra-red detectors.
A heat signal was picked up indicating hot magma rising to the surface. Success in predicting eruptions in this way has been experienced in other areas as well. However, in some areas the sheer number of volcanoes combined with the poverty of the area means the technique is less useful. Where it can be used, it can however provide valuable hours or even days in which to evacuate people from areas facing an impending eruption.
Seismicity
Earthquake activity can often increase prior to a volcano as magma and gas rises. The rising magma and gas can cause vibrations and trigger earthquakes. Scientists monitoring seismicity (earthquakes activity) in volcanic areas can detect an increase in earthquakes and the type and intensity of the activity can be used to determine when an eruption is occuring.
Ground Deformation
As magma rises it can cause a change in the shape of a volcano. Changes in the ground may include subsidence, tilting, or even the formation of a bulge when the magma rises. Remember, during the lead up to the eruption of Mt St Helens a cryptodome formed on its side due to the rising magma. Tilt metres, surveying techniuqes and even satellite imagery can all be used to detect and monitor ground deformation.
Volcanic Gases
The build up of gases are one of the driving forces of volcanic eruptions and monitoring gases such as sulphur dioxide can be important in the prediction / monitoring of volcanic activity. An increase in sulphur dioxide emissions can reflect rising magma. Likewise, a sudden decline in sulphur dioxide emissions following a period of rapid increase can suggest some blockage which may result in the build up of pressure prior to eruption.
Hazard Assessment
Hazard Mapping. Being prepared for volcanic events can ensure the saving of many lives through successful evacuation. As well as careful monitoring of volcanoes and the implementation of carefully thought out evacuation plans, hazard mapping can help to determine the areas most at risk from an eruption by taking into account the behaviour and hazards associated with previous eruptions in order to help determine which areas most at risk and thus to determine evacuation zones.