Prediction of Hazard Events (AQA A Level Geography)

• Volcanic eruptions occur with varying frequency and regularity depending on the type of volcano and its location
• Shield volcanoes tend to be found at constructive plate margins and are typified by high frequency, low magnitude eruptions
• Stratovolcanoes tend to be found at destructive plate margins and are typified by low frequency, high magnitude eruptions

Diagram of a shield volcano

Diagram of a stratovolcano

• Some volcanoes erupt more frequently and regularly than others
• Mount Stromboli in Italy usually erupts every 20-40 minutes
• Mount Pinatubo in the Philippines had not erupted for around 500 years before its eruption in 1991
• Scientists study the geological history of volcanoes (e.g. eruptions and gas emissions) to try to predict when the next eruption might occur
• Volcanic eruptions can occur with few warning signs and do not necessarily follow historical patterns

• There are warning signs before most volcanic eruptions
• Volcanologists (scientists who study volcanoes) monitor changes using GPS, tilt meters, satellites, seismometers and gas detection
• Signs of an eruption include:
• Magma rising which can be detected by heat sensors and satellites
• Ground deformation as rising magma causes bulges
• Increased emissions of sulphur dioxide and other gases
• Increased seismic activity caused by magma movement detected by seismometers

Methods of monitoring volcanoes