KNMI volcanologist explains why eruptions don’t suddenly happen

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PHOTO CAPTION: Mt. Scenery

SABA–A volcanic eruption doesn’t suddenly happen: usually it is a process that evolves over a longer period of time which is accompanied by signals of the volcano’s increased activity.
Volcanologist Elske de Zeeuw-Van Dalfsen of the Royal Netherlands Institute for Meteorology (KNMI) explains why people on Saba don’t have to worry about a sudden eruption. “There are usually signals when a volcano becomes active. The data will show increased activity, and people will also observe changes, such as a sulfur smell.” Upon receiving these signals, both in data and observations, the KNMI will immediately act and analyze the situation.
De Zeeuw-Van Dalfsen gave St. Vincent as an example. Six weeks before the Soufrière volcano started showing visual signs of activity, there were multiple earthquakes and a thermal satellite image prompted the National Emergency Management Organization to visit the crater where they saw the start of a dome. Local authorities, together with the University of West Indies (UWI) Seismic Research Center, installed additional monitoring equipment. This equipment usually consists of cameras and reflectors to measure the changes (e.g. growth) of the dome from a safe distance. Samples have also been taken of the slow growing dome to analyze the geochemical composition. The UWI Seismic Research Center provides daily updates to the public.

Code green
“All sorts of measures have been taken in St. Vincent. That would also happen on Saba, if the Mt. Scenery volcano were to become active. The Saba volcano is and has been for a very long time on code green, meaning that there is no abnormal activity. There is, what we experts call, normal background activity,” said De Zeeuw-Van Dalfsen. A normal activity, for example, is the hot spring near Green Island, which has been at a constant 82 degrees Celsius.
Stepping up the monitoring of a volcano only makes sense if there is increased activity. Otherwise, there is nothing to monitor. In case Mt. Scenery would show increased activity, a team of the KNMI will immediately spring into action. Additional instruments would be installed. The team can also request assistance of experts from St. Vincent and Montserrat. Experts in the region are in close contact and assist each other in case a volcano shows increased activity. A team of Montserrat for example is currently assisting St. Vincent.
The Caribbean has a number of volcanoes. The majority have the activity status green (normal), while some are yellow (advisory): La Soufrière in Guadeloupe, Mt. Pelée in Martinique, Kick ‘em Jenny above Grenada. Only La Soufrière in St. Vincent is orange (watch). One or more volcanoes showing increased activity doesn’t mean that the others in the region will become active too. “They are not connected. They all have an individual plumbing system, so to speak,” said De Zeeuw-Van Dalfsen.

Montserrat eruption
When in the 90’ies, the Soufrière Hills volcano in Montserrat erupted, nothing happened on Saba. “People on Saba at that time occasionally smelled sulfur drifting over from Montserrat, but not much more than that. St. Vincent is much further away from Saba, so even if St. Vincent would erupt explosively, Saba won’t notice the direct effects.”
Chances of a sudden, catastrophic eruption such as Mt. Vesuvius near Pompeii, Italy in the year AD79, are extremely small. “In order for an eruption to take place, the magma needs to come up. This will be noticed by the measuring equipment and people will notice it too,” said De Zeeuw-Van Dalfsen.
In the case of the Mt. Pelée 1902 eruption in Martinique, there were clear signals in the preceding weeks. “There were indications of an imminent eruption, but they were underestimated. Now, we have much more know-how and very precise measuring equipment. We notice changes in volcanoes’ activities. In 1902, no evacuation took place in Martinique. Naturally, we would do so if this were to happen in current times.”

Evacuation
Evacuations have not taken place in St. Vincent yet, but the authorities are on high alert and the people are being constantly informed and prepared for a possible evacuation. “Geologically speaking, there is normally sufficient time for an evacuation. In general, you see a gradual increase in a volcano’s activity which can take months to years,” assured the KNMI volcanologist. The last eruption of La Soufrière in St. Vincent was in 1979.
Whether or not to evacuate the Saba population if Mt. Scenery was to show intense, dangerous activity, is not a decision that the KNMI would take. However, the KNMI does advise the local authorities about the status of the volcano. Based on this advice, authorities would then take a decision. Saba has a disaster/evacuation plan in place. The KNMI has been monitoring on Saba since the end of 2006. The KNMI website has more info about volcanoes, on Saba, but also the other islands: www.knmidc.org/volcanoes

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