There was another explosive eruption of the La Soufriere Volcano in St Vincent shortly before midnight last night, on a day that pyroclastic flows reached the sea on the island’s west coast.
And the scientists have noted a change in the seismic activity, with what was described as “long period earthquakes” increasing in numbers.
Long period earthquakes are produced by vibrations generated by the movement of magma within the volcano, when pressure within increases and the surrounding rock fails, creating small earthquakes, a precursor to a large eruption.
The La Soufriere has been eruptive since last Friday, with a warning that it could go on for months.
Entire towns and villages in the northern Red Zone of St Vincent have been evacuated ahead of the ashfall that has destroyed buildings and the agriculture, with an estimated 16,000 people having moved to safer areas and housed in State shelters and private residences.
A humanitarian relief effort is underway.
No deaths or serious injuries have been recorded, and credit for the early warning and evacuation advice has gone to The UWI Seismic Research Unit monitoring the activity on the volcano since it awoke last December and began spewing lava and building a dome.
The team noted overnight that Seismic activity changed with the explosive activity at 6:30 am on Tuesday morning, the anniversary of the 1979 eruptions of the La Soufriere which were smaller and less destructive.
The scientists said that prior to Tuesday morning’s explosion, long-period earthquakes had been increasing in number, accompanied by larger seismic tremor which was followed by over three hours of smaller continuous seismic tremor, lasting seconds to minutes.
This explosion produced the dreaded pyroclastic flows that reached the sea at the mouth of the Wallibou approximately six kilometres from the volcano, and the ash column rose as high as 20 kilometres.
The pyroclastic flows reached the sea in every valley extending from Larikai to Wallibou on the island’s west coast.
The scientists are warning that more explosive eruptions, pyroclastic flows and ashfall can be expected over the next few days.
The pyroclastic flow
Pyroclastic flows are super heated, ground-hugging flows of ash and debris can travel at speeds of hundreds of metres per second, reaching many tens to hundreds of kilometres from the source, typically following valleys.
With rock fragments ranging in size from ash to boulders that travel across the ground at speeds greater than 80 kilometres per hour, pyroclastic flows knock down, shatter, bury or carry away nearly all objects and structures in their path. The extreme temperatures of rocks and gas inside pyroclastic flows, between 200°C and 700°C, can ignite fires.
Nothing can survive.
