On January 4th of 1880, a powerful explosion was heard throughout the Caribbean Island
of Dominica.
What had just occurred was a powerful explosion equivalent in energy to the detonation of
30 tons of TNT.
Yet, this was not a purposeful explosion by miners, nor was it an industrial accident.
As instead, this blast was volcanic in origin.
As people looked around for the source, a plume of thick gray ash rose into the atmosphere,
rising to a height of 10,000 feet.
Due to the winds which were blowing to the west at the time, ash from the volcanic eruption
began to fall on a nearly 60 square kilometer section of the island, going on to coat the
landscape in half a centimeter thick of fine ash in the town of Roseau.
The next time rain fell, fresh ash was rapidly swept into the Roseau River, creating a lahar
which swept downstream all the way to the coastline.
What had just occurred from a phreatic volcanic eruption, aka a volcanic eruption that was
essentially a large steam explosion triggered by the heat of underlying magma, originating
from a section of the Morne Watt volcano's numerous hydrothermal features in a region
which is known as the Valley of Desolation.
This eruption thankfully only left behind minor damage, and registered in on the 0 to
9 volcanic explosivity index as a 2.
During the last 1 million years, the island of Dominica has been one of the most volcanically
active regions in the entire Caribbean.
As, this marks the approximate time when volcanic activity dominantly in the north of the island
suddenly moved toward the south of the island.
This caused numerous volcanic centers to pop up, creating between 3 and 7 volcanic complexes.
This number varies as some authors consider each complex to be separate, while others
consider several features deemed as separate complexes by other authors to be part of a
single complex.
These complexes have over time created an incredibly rugged and steep landscape through
the creation of numerous steep sided lava domes, hydrothermal alteration, and associated
landslides and erosion which created deep valleys.
The Morne Watt volcanic complex consists of 4 small stratovolcanoes which each contain
lava domes along with a single large hydrothermally active region which is known as the Valley
of Desolation.
These vents largely follow a natural graben or fault line on the island, meaning the specific
volcano exists not only due to subduction but also because it represents a path of least
resistance for magma to intrude into the crust at.
The Valley of Desolation contains more than a combination of a dozen fumaroles and hot
springs spread across three distinct regions.
The most notable of these hot springs is referred to as the Boiling Lake, which due to a combination
of changes in the amount of monthly precipitation and possible magmatic activity at depth, has
its water level notably vary, with a lower level potentially but not always being a cause
for concern.
The present fumaroles continuously vent volcanic gasses which include carbon dioxide and sulfur
dioxide, with these gasses being sourced at a magma chamber below which is probably at
its shallowest point still 6 kilometers deep in the crust.
The Morne Watt volcanic complex which covers 2.9% of the island has been intermittently
erupting for 460,000 years.
These eruptions did not really follow a trend but rather occurred fairly randomly at 5 different
points.
Eruptions primarily consisted of the growth of gray colored andesite lava domes.
These lava domes would then intermittently produce partial collapses, leading to the
generation of pyroclastic flows which could travel up to 5 kilometers distant in what
is known as a Merapi type vulcanian eruption.
Some highly explosive pelean style eruptions also occurred, but eruptions of this magnitude
have not occurred in more than 1,000 years.
Here is a quick overview of when the last eruption from each of the 4 stratovolcanoes
and group of hydrothermal vents within the Morne Watt complex occurred.
Overall, Morne Watt has erupted 9 times in the last 11,000 years, and 4 times in the
last 2,000 years.
Its last eruption was a very small phreatic eruption in 1997, which occurred within the
Valley of Desolation.
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