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 suface 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 (see below).
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 valauble hours or even days in which to evacuate people from areas facing an impending eruption.
See also the USGS overview of Remote Sensing for Monitoring Volcanoes
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. For further information see the USGS overview of Monitoring Volcano Seismicity
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. For more information on the techniuqes used, see the USGS overview of Monitoring Volcano 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. For more information on the measuring of gas emissions, see the USGS overivew of Monitoring Volcanic Gases
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.
This is an example of a Hazard Zonation map for Mount St Helens - it comes from the USGS's report on Volcanic-Hazard Zonation for Mount St Helens, Washington, 1995 (USGS) - the report considers areas that are most likely to be at risk (known as hazard zones) during future eruptions. The zonation takes into account experience during previous major eruptions such as the 1980 eruption as well as monitoring of changes in the volcanoes hydrology, topography and geology.
See USGS - Volcano Hazard-Assessment Techniques.
Research into volcanic risk and hazard management can help in a number of ways, but the messages don't always work, for example due to distrust in information sources or public apathy resulting from long periods of inactivity by some volcanoes. This poster explores the dangers of volcanoes, why lives are still lost, how research can help and why messages of warning / prediction don't always work.
Follow Up Links:
Wikipedia - Volcano Prediction - a comprehensive account of general principles and methods of volcano prediction / monitoring
Discovery Channel - Monitoring and Predicting Volcanoes
USGS Cascades Volcano Observatory - Volcano Monitoring Overview
Deadly Shadow of Vesuvius - Can we predit Eruptions?
Prediction of Danger - methods and instructments of monitoring
Volcanoes - Can we predict Volcanic eruptions?
Volcano Monitoring Techniques
USGS Overview - Volcano-Monitoring Techniques
Key Term Check:
Remote Sensing - the use of satellite imagery to detect clues of volcanic activity which are beyond the normal range of human revision, using ultra-violet, infra-red and microwave sensors. As well as tracking eruption clouds, thermal-sensing can be used to detect hot features on volcanoes which can indicate areas where magma is rising closer to the surface.
Ground Deformation - this refers to changes in the slope / shape of a volcano which can indicate the rising / build of magma. (think about the cryptodome which grew on the North flank of Mount St Helens prior to its eruption in 1980)
Hazard Mapping - a technique used to map out areas most at risk during future eruptions and the likely hazards (this mapping is based on experiences during past eruptions)
Seismicity - this simply refers to earthquake activity (which frequently preceeds / accompanies volcanic eruptions).
Photo courtesy of USGS
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