How to predict a volcanic eruption
Every year some 60 volcanoes erupt around the world and some of them erupt as often as every day such as Kilauea and Stromboli in Hawaii. Most of the eruptions are luckily enough quite weak, but every now and then there are devastating eruptions that kill thousands of people such as the eruption of Ruiz, Colombia, in 1985 which killed over 25 000 people .
The size of a volcano eruption is very difficult to measure as there are many things that need to be taken into account, such as what type of volcano it is, its volume, plume height and other observations made during an eruption. Volcanologists use an eruption magnitude scale to be able to compare the size of various eruptions. The scale is called the Volcanic Explosivity Index (VEI). The VEI scale has nine steps starting at 0.
A volcano eruption of grade 0 is non-explosive and has a plume height of less than 100 m. A grade 1 eruption has a gentle explosion and a plume height between 100 and 1000 m. Eruptions of grade 0 and 1 are very common and occur daily. Explosive eruptions of grade 2 with plume heights of 1-5 km occur weekly and severe eruptions of grade 3 with plume heights of 3-15 km occur about once a year. Grade 4 eruptions happen about every ten years and they are described as cataclysmic, with a plume height of 10-25 km.
Eruptions of grade 5, 6, 7 and 8 all have plume heights higher than 25 km. The eruption at Mt St Helens in Washington State, which killed 61 people and thousands of deer and other animals in 1980, was a paroxysmal eruption of grade 5. Grade 5 and colossal grade 6 eruptions occur about once in a 100 years. And super-colossal eruptions of grade 7 happens about once in a 1000 years.
Mega-colossal eruptions of grade 8 such as the one in Yellowstone 640 000 years ago happens about once in 10 000 years. The world’s highest concentration of geysers and other thermal features found in the Yellowstone area is evidence that the volcano is still active but according to scientists the area should still be safe to visit as there are many ways to predict a potential eruption.
The first signs of an oncoming eruption are usually ground movement and ground deformation in the surrounding area of the volcano. Before an eruption magma rises and as it pushes its way upwards it causes the ground to tremble and deform. The ground close to active volcanoes is measured and monitored by scientists in order to spot any changes that could mean the onset of an eruption.
Cracks in the ground can let gases out and any unusual gas emission is another sign of eruptive activity. Scientists use correlation spectrometers to measure any changes to the gas composition.
As it is usually too dangerous to put any instrument near the crater of an active volcano satellites are used to monitor and measure infrared radiation. Any sudden changes in heath activity can be a sign of an oncoming eruption.
The groundwater can also give clues to an oncoming eruption. Changes to the groundwater temperature, the stream-flow and sediment transportation and lake levels are studied by scientists.
Even if it is possible to spot the signs of an oncoming eruption, it is still very difficult to predict when an eruption will take place. Depending on the volcano, scientists will get anything from a few days up to a few months notice.
The best way to stay safe is of course to avoid areas with eruptive activity but as the flanks of volcanoes often tend to have fertile soil lots of people around the world live under the threat of an eruption. Evacuation plans have been developed for these areas and radio messages will be sent out to warn and guide people in case of an emergency. FEMA provides good information about what areas are at risk and what to do if a disaster should happened.