Monitoring the flux of SO2 is critical to fully understand the current state of an active volcano. Increases can indicate the injection of a new batch of volatile-rich magma, which in turn can lead to an increase in the explosivity of the volcano. On-the-other-hand, a reduction in flux may indicate increased sealing of the system, which might result in explosive decompression.

1. Aerial - most accurate since wind speed can be measured in the plume and the measurement is taken at a close distance. Plane flies below plume with instrument pointing up.
2. Land traverse - when wind direction allows it, a vehicle traverse can be made below the plume.
3. Fixed measurement - this is the least accurate since there are large geometrical errors, however, often it is the only available method. It is more convenient for taking repeating measurements to measure total volumes released in explosive events.

Ideally these measurements should be carried out at least once per week. During 2007, two scanning stations will be installed to enable continuous data to be collected.

Measuring SO₂ release from explosions