La Soufriere eruptions continuing to decline-scientist
La Soufriere volcano is showing a declining pattern of eruptions, but at the same time, there is more steam being observed coming from the summit.
Scientists monitoring the volcano have said the steam may be because we are in the rainy season and the added precipitation may be interacting with magma at the summit, and creating phreatic eruptions.
These eruptions occur when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from 500 to 1,170 °C) causes near-instantaneous evaporation of water to steam, resulting in an explosion of steam, water, ash, rock, and volcanic bombs.
Lloyd Lynch, lead Scientist monitoring the volcano gave this observation on Wednesday during an update on NBC Radio’s Eyeing La Soufriere program.
Lynch, who is attached to the University of the West Indies Seismic Research Unit (UWI-SRC), explained that they have observed periodic bursts of a high level of steaming occurring on average every 30 minutes.
“We don’t know if it is being caused by water due to rainfall, but this is why it is important to have improved monitoring at the crater so we can correlate…,” Lynch noted, while also explaining that an increase in seismic activity is about high frequency vibrations, but from his experience this looks like steaming.
He noted that they have also seen a slight increase in seismicity, “very slight on average…we have been recording less than 10 earthquakes…over the last 24 hours they were 11, slight increase there,” he said on Wednesday.
Gas monitoring done on Tuesday returned 352 tonnes per day, the previous figures were 290 tonnes and before that, 500 tonnes.
“…So there is some fluctuation overall, an average about 550 tonnes. So the last two readings were below average ,so there is some decline there if you look at the short term average,” Lynch said adding that without all the monitoring equipment being installed it is hard to monitor accurately what is happening.
“What is important in monitoring is to maintain a high level of surveillance and have a system working at all time,” Lynch said.
He said one of the parameters they usually monitor on the volcano is ground swelling, because as new magma comes to the surface, it causes the ground to swell and the level of swelling, in most cases, is not enough for one to discern with their eyes.
He said further that they are hoping to install instruments called tilt-meters at the geothermal site at Bamboo Range, at the Richmond Vale Academy and at the summit, when it is safer.
A tilt-meter is a sensitive inclinometer designed to measure very small changes from the vertical level, either on the ground or in structures. They can record angular changes of the order of micro radians.
Explaining how a tilt-meter works, Lynch said,“…if you consider a long steel rod, half a mile long, and you lift it to put a 10 cent underneath…the angle at the other end is small but it can detect it, it is very sensitise…”.
Lynch noted that during the earlier phases of the eruption, he liaised with the manufacturers of the tilt- meter and they donated three. He said one cost between US$11,000/US$12,000, so the Unit was very fortunate to get the donation.
Lynch said also that they will soon have helicopter support which will give them a chance to do close up monitoring including cameras, a tilt-meter and a seismic station at the summit.
“We need to do more close up monitoring,” he stressed, while reminding that a lot of equipment were destroyed during the eruptions.
He said as we move further into the rainy season, they expect changes in the wind pattern and the level of precipitation, and this will influence what they see from the volcano.
Lynch noted that a change in wind pattern is likely to change the intensity of the gas that a particular area is exposed to.
He added also that the water table will rise and with the volcano still having hot material at the top, they expect the water table will interact with the hot material and that will create phreatic eruptions once there is sufficient level of water interaction, and if the timing of the interaction is sufficient.