Volcanic hazards Spatial distribution Magnitude Frequency Regularity Predictability

Spatial distribution of the most deadly volcanic eruptions 75% of all volcanic material is erupted at constructive margins but…

Magnitude The magnitude of volcanoes is measured using the VEI scale (volcanic explosivity index). It is a logarithmic scale meaning each unit of the scale = 10 times increase in volume of material erupted.

Magnitude

2 volcanoes with the same VEI…

Frequency

Frequency VEI vs. eruption frequency: This chart shows how small, less explosive eruptions are much more frequent than large eruptions. This database includes recorded and historic eruptions that occurred between about 10,000 years ago and 1994.

Regularity

Stromboli in Italy This stratovolcano in Southern Italy has been erupting almost continuously since 1932. This make it one of the most active volcanoes in the world.

Eyjafjallajokull in Iceland Eyjafjallajokull erupted in 920, 1612, 1821 and 2010. However, Iceland experiences a volcanic eruption once every 10 years.

Mt Pinatubo in the Philippines Mt Pinatubo erupted in 1991 after remaining dormant for over 600 years. Even the indigenous Aeta highland population who inhabit the flanks of the volcano did not have any reference to a previous eruption in their oral histories. Previous eruptions are thought to have occurred around 15,000BC, 7,000BC, 4,000BC, 1900,BC and AD1500

Predictability Nowadays active volcanoes all over the world are monitored using a vast array of scientific equipment. Satellites look for infrared radiation that indicates rising magma and ground instruments measure gas emissions, ground deformation and resulting earthquake activity. Geologists use evidence from past eruptions to suggest likely eruptive scenarios and hazard maps can be constructed to indicate those areas at greatest risk. Scientists can provide reasonably accurate forecasts of impending eruptions and people can be evacuated from areas considered to be at risk. Such forecasts and evacuations were particularly successful for the Mt St Helen’s eruption in 1980 and the eruption of Mt Pinatubo in 1991, and the eruption of Soufriere Hills on Montserrat in 1997. However, governments do not always respond to scientific predictions and disasters can result. For example, in1985 despite warnings of an impending eruption with associated lahars, the government of Colombia failed to order an evacuation and 25,000 people lost their lives in the town of Armero when the volcano Nevado del Ruiz erupted. Scientists do not always get it right and sometimes eruptions that seem imminent never actually occur. This reduces the scientists’ credibility in the eyes of governments and local people and can cause problems the next time an eruption seems likely.

Deadly nature of a volcano = ?? What equation could you make to predict how devastating a volcanic eruption could be: Deadly nature of a volcano = ??