Volcanic Surveillance is based on the assumption that movement of molten rock or magma beneath a volcano will occur before any eruption can start and this movement of magma is detectable using various methods. Volcanologists use many techniques to monitor an active volcano; some of the main techniques are:
- Visual and Cameras — The cheapest way of monitoring a volcano is just by looking at it!
- Seismic Monitoring — Seismic monitoring is the most widely used of the 'holy trinity' of volcano monitoring methods – seismic, deformation and geochemistry. Worldwide, almost all monitored volcanoes have some kind of seismic monitoring system and it is usually the first technique applied when scientists begin to monitor a volcano.
- Ground Deformation — One of the key techniques used in volcano surveillance is monitoring ground deformation.
- Chemistry — As the molten material (magma) rises to shallow levels, gases are released and they rise to the surface.
- Gas — When molten material (magma) moves into a volcano it gives off volcanic gas emissions, sulphur dioxide (SO2), carbon dioxide (CO2) and hydrogen sulphide (H2S) which are measured regularly at our volcanoes. There are several techniques which include measurement done from an aircraft and on the ground. The four primary techniques, two airborne and two ground-based are outlined below.
- Crater Lakes — When volcanic craters cool down after major eruptions, they often fill with water to form crater lakes. Some are cool, just filled by rain water, while others are warm or hot and remain connected to the volcanic plumbing. The colour of crater lakes varies markedly according to the temperature and chemistry of the water, and the type and concentration of particles suspended within it.