Volcanic Surveillance

Volcanic surveillance is based on the assumption that movement of molten rock or magma beneath a volcano will occur before any eruption can start. Check out a video of our scientists monitoring White Island.

  • Visual observation
  • Ground deformation
  • Chemical analysis
  • Seismic monitoring

Ground Deformation

Ground Deformation
As the magma approaches the surface of the earth, and moves into the conduit below the vent of a volcano, the pushing aside of the surrounding rocks to make way for the magma causes the ground surface to move and the volcano to swell. This rising or swelling can be detected by ground deformation surveys using levelling, triangulation and GPS surveys.

Chemical analysis

Chemical Analysis
Magma deep in the earth contains gases dissolved in it. As the magma rises to shallow levels, these gases are released and, because they are so mobile when compared to the sluggish liquid magma, they rise to the surface and are discharged through gas vents as fumaroles. The temperatures and absolute amounts of the gases and for the relative proportions of different gases give information on the state of the magma and how close to the surface it is. In some cases, notably Ruapehu, these gases emerge under a lake, and the chemistry of the lake water is then used to work out how much volcanic gas is being released

Siesmograph

Seismic Monitoring
Earthquakes commonly provide the first indication of volcanic unrest. Volcano-seismic networks are in operation around New Zealand's volcanoes in the Taupo Volcanic Zone, Taranaki, Auckland and on Raoul Island.

Volcanic Earthquakes are caused when the rocks are broken by the magma moving through them. If the rocks are relatively cool and brittle, then the earthquake will be a higher frequency than those that break hot-softer rocks.

Volcanic tremors
Are caused when the hot volcanic gases escape from the magma. As they pass through cracks on the way to the surface they cause a small ground vibration. This can be an almost continuous signal. Volcanic tremor can also be caused by the movement of molten magma.