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Volcanic eruptions are unpredictable - however, scientists can monitor volcanoes to estimate when they are likely to erupt. Scientists can use a variety of techniques to do this, such as:

• seismometers - used to measure earthquakes occurring near an eruption
• tiltmeters and GPS satellites - these devices monitor any changes in landscape - volcanoes tend to swell near an eruption
• monitoring gases escaping from a volcano using robots called Spiders -- often there is an increased release of sulphur dioxide near an eruption, as the magma gets closer to the surface
• measuring temperature - volcanoes become hotter when magma starts to rise through the main vent
• looking at the past history of eruptions - scientists can identify patterns of activity