The Bottom, Saba -The Department of Seismology and Acoustics of the Royal Netherlands Meteorological Institute (KNMI) has been working on Saba for several years to monitor the dormant volcano Mount Scenery. The monitoring of a volcano is best done using multiple techniques to assess the state of activity.
One way to monitor is through a so-called Global Navigation Satellite System (GNSS). In January 2018, the KNMI installed the first GNSS at St. John’s, followed by a second installation at the Juancho Yrausquin Airport in February 2019. Both instruments are operating as expected and data are automatically sent to the KNMI in the Netherlands every hour, using a transmission facilitated by SATEL.
The GNSS instruments have to be regularly maintained to ensure their continued operation. The instruments are subject to the harsh environmental conditions: the chloride ions in the air from the evaporated sea salt in ocean spray and the high temperatures speed up the reaction time, corroding even stainless steel. A GNSS instrument measures the distortion of the earth’s surface, making it possible to see whether the surface swells or deflates.
A second way to monitor is through temperature sensors. In January 2018, a temperature sensor was installed at the hot spring opposite Green Island. This sensor takes a measurement every 20 minutes and stores the data locally. The measurements form a time series which gives more detailed information about temperature changes of the hot spring and is compared to the single measurements that have already been taken.
If the volcanic activity changes, the temperature of the hot spring can increase. There will also be more fumes, said KNMI volcanologist Elske de Zeeuw-Van Dalfsen of the Department Seismology and Acoustics. She asked people to let the KNMI know through the safety coordinator of the Public Entity Saba when they notice fumes or any other possible volcano related activities.
The last visit of the KNMI to the hot spring was in February 2019. Improvements were made to the installation, which includes temperature probes that are buried in the ocean bed and covered with rocks to keep them in place, and data loggers, small yellow cases mounted on the rock above the spring and housed in a black case to protect it against the elements. Due to the high surf activity, it remains to be seen how long the temperature probes and their cables will survive. A more rugged installation is planned for the future.
The third monitoring instrument is the seismometer. The KNMI has installed three seismometers on Saba: in The Bottom, St. John’s and Windwardside. A fourth seismometer will be reinstalled shortly at the airport after the instrument has been repaired. Seismic instruments are important because they record the vibrations of the earth. If a volcano becomes active, the seismic vibrations will intensify, explained De Zeeuw-Van Dalfsen. KNMI representatives visit Saba on a regular basis.
The seismic network is designed to monitor the seismicity in the Caribbean Netherlands region and the seismic signals preceding or accompanying the volcanic activity of Mt. Scenery. The Quill on St. Eustatius is also being monitored. Furthermore, the seismic network contributes to the detections of earthquakes in the region, which may generate tsunamis. The seismic network has been gradually expanded since 2006.
The current monitoring network of Saba is in development. The goal is to enhance the monitoring capability. Future improvements include 1) the installation of a seismic station in the north west area of Saba, 2) the placing of another GNSS station on the island and 3) installing a more durable temperature sensor which transmits data in real-time to monitor the hot spring on Saba.
The first scouting for potential sites to fulfill point 1) was done in early 2018. One potential site was identified, but because there are no power or communication facilities available at the location, installation will be more complex and will require solar panels and a battery as well as a way to transmit data to KNMI. More investigations are needed to successfully complete this task in an affordable way.
Setting up a monitoring network requires time, effort, and finances and can be complicated in areas that are not in close proximity to the monitoring agency, in this case KNMI. Continued support, financially and scientifically, as well as from the local government and populace, is required to sustain such a network, stated De Zeeuw-Van Dalfsen who together with her colleague Reinoud Sleeman published a comprehensive article about the monitoring network of Mount Scenery and The Quill in the August 2018 edition of the scientific magazine Geoscience. The Dutch government has a task to secure people’s safety in the Caribbean Netherlands, and this means making investments in a solid monitoring system of Mount Scenery.
To enable the observation of changes in geophysical parameters and to ensure timely warning, a monitoring network needs to be operational even when volcanic activity remains at background levels. More specifically, it is crucial to establish a monitoring network before any activity takes place. Despite the fact that sustaining such a network in tropical conditions remains a challenge, it is the only way to ensure that potential future volcanic activity is detected in advance, benefiting the safety of the local populations.
Saba consists of the stratovolcano with multiple andesitic domes on the flank of Mount Scenery. The most recent eruption may have taken place around 1640. And, even though Mount Scenery is officially a dormant volcano, it is possible that it becomes active. An example of a dormant volcano suddenly becoming active is Montserrat’s Soufrière Hills which erupted in 1997 after some 350 years of dormancy. That is why monitoring remains important.