Volcanoes can be monitored by considering the seismic activity and the amount of gases being released. Infrared cameras can also be used to detect magma movement.

A logarithmic scale where the energy release is proportional to the scale of the event. Each unit of increase on the scale equates to approximately 30 times the increase in energy, mainly felt through vibration.

A qualitative scale which measures the impact of the event. The scale has 12 points. At each point there is a description which increases in severity through to total destruction.