SABA–A volcanic eruption does not suddenly happen: usually it is a process that evolves over a longer period of time accompanied by signals of the volcano’s increased activity.
Volcanologist Elske de Zeeuw-Van Dalfsen of the Royal Netherlands Meteorological Institute KNMI explains why people on Saba do not 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 sulphur smell.” On receiving these signals, both in data and observations, the KNMI will immediately act and analyse 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 Organisation to visit the crater, where they saw the start of a dome.
Local authorities, together with The University of West Indies (The UWI) Seismic Research Centre, installed additional monitoring equipment, which usually consists of cameras and reflectors to measure changes, such as growth of the dome, from a safe distance. Samples have also been taken of the slowly-growing dome to analyse the geochemical composition. The UWI Research Centre provides daily updates to the public.
“All sorts of measures have been taken in St. Vincent. That would also happen in 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. 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. If Mt. Scenery were to show increased activity, a KNMI team would spring into action immediately. 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 if a volcano shows increased activity. A team from Montserrat, for example, is currently assisting St. Vincent.
The Caribbean has a number of volcanoes. The majority have green activity status (normal), while some are on yellow advisory, such as La Soufrière in Guadeloupe, Mt. Pelée in Martinique and Kick ’em Jenny above Grenada. Only La Soufrière in St. Vincent is on orange watch.
One or more volcanoes showing increased activity does not 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.
When the Soufrière Hills volcano in Montserrat erupted in the 1990s, nothing happened in Saba. “People in Saba at that time occasionally smelled sulphur drifting over from Montserrat, but not much more than that. St. Vincent is much farther away from Saba, so even if St. Vincent erupted explosively, Saba wouldn’t notice the direct effects.”
Chances of a sudden, catastrophic eruption such as Mt. Vesuvius near Pompeii, Italy, in the year 79AD, 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 eruption in Martinique in 1902, 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.”
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 were to show intense, dangerous activity, is not a decision 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 in Saba since the end of 2006. The KNMI website
www.knmidc.org/volcanoes has more info about volcanoes in Saba, but also the other islands.
Bron: Daily Herald