Before a volcanic eruption, magma rises towards the surface. There is a reduction in pressure and therefore gases tend to escape.Increase in emissions before an eruption (but a decrease in gas emissions suggests a blocked vent)
As a result of this, sulpher dioxide and carbon dioxide emissions are continuously monitored on active or potentially active volcanoes
Escape of gases is related to supersaturation
- sulphur dioxide is the prominent volcanic gas
- gases are supersaturated in the magma - normally the solvent magma would not be able to hold such high quantities, but under high temperature and pressure they are successfully dissolved.
Fumaroles (fume-holes)
- sights of gas release on the slopes of any active volcanoes
- before an eruption fumarole activity will increase greatly
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