Recording the frequency and strength of volcanoes, as they are a frequent sign of an impending eruption.
Tiltmeters can identify small, subtle changes in the landscape, as 'swelling' can show an eruption will occur.
For example, the bulge that appeared on the northern side of Mount St Helens.
GPS (Global Positioning Systems) use satellites to detect movement of as little as 1mm.
The change in surface temperature can been seen on satellite images.
Digital cameras placed on the rim of craters can photograph events relatively safely.
Monitoring sulphur dioxide levels in the gas emitted - there is an increased amount of sulphur dioxide in vent gases before an eruption.
Robots called 'spiders' are used to monitor changes - the past frequency of eruptions, the gaps between them; the pattern of lava flows; ash movements and lahars can tell us about how the volcano is likely to behave.
Monitoring volcanoes is essential because it allows people to prepare for an eruption by organising the evacuation of people and arranging supplies.
Prediction and Planning for Future Eruptions: UN Recommendations for Surveillance
Regional network of seismographic stations that should be set up in populated risk areas.
Portable seismographs and tiltmeters should be available for an volcanoes showing signs of activity
Trained volcanologists should be made available to interpret events.
Detailed histories of volcanoes should be produced, but not all volcanoes have a cycle.
Detailed maps should be produced to show deposits of lav and pyroclastic materials from previous eruptions; these could show areas at risk.
Periodic measurements of possible changes in temperature and pressure within the volcano. Chemical analyses of fumaroles and hot springs could indicate a variation from the norm.
Infrared photos could show a build-up in temperature and any possible swelling/bulging of the cone.
Emergency procedures, including evacuation procedures should be established for all communities.
These procedures are easier to adopt in:
MEDCs with greater wealth and technology.
Areas where the expected frequency of the event is high.
In risk areas with high population densities.
Vent: The opening - usually central and single - in a volcano, from which magma is emitted. Lahars: These secondary effects of a volcanic eruption are mudflows, resulting from ash mixing with melting ice or water.