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Introduction

Volcanic Hazards
Lava Domes & Pyroclastic Flows Page 7
Pyroclastic Surges & Ashfall Page 8
Bombs, Lahars, P-M Eruptions Page 9
Monitoring & Forecasting Page 10
Earthquakes, Ground Def Page 11
Gas & Water, Gravity Page 12

Scientists

Emergency Managers

The Media

Appendices
Communication During Volcanic Emergencies
An Operations Manual for the Caribbean

Associated terms:
COSPEC
FTIR

The escape of magmatic gases from beneath the surface is monitored by measuring changes in the amount and composition of gases being released at fumaroles and seeping into the atmosphere from the soil. The rise of magma may be reflected in greater concentrations of sulphur dioxide (SO2) in fumaroles, or radon and helium in soil gases. Once a volcano is active, the SO2 concentration in any gas plume from the vent can be determined using a Correlation Spectrometer (COSPEC). Other gases may be detected using a newer method known as Fourier Transform Infrared Spectroscopy (FTIR). Magmatic gases may also be detected in water from springs and wells.



Associated terms:
Microgravity
Gravimetry
Gravity meter
Gravimeter

The movement of magma below and into a volcano changes the distribution of mass and density beneath the surface, which in turn modifies the local pull of gravity. The magnitude of the change is tiny - a few tens of millionths of the average strength of the Earth's gravity - and can only be detected by very sensitive instruments called gravimeters or gravity meters. The local pull of gravity is also affected by ground swelling, so to be meaningfull gravity measurements must be combined with techniques capable of accurately measuring surface deformation.

Fig 10. Microgravity monitoring