ISLAND PROFILES
St. Lucia - Geothermal Activity
The well-known Sulphur Springs of Saint Lucia is the hottest and most active geothermal
area in the Lesser Antilles. The main area of Sulphur Springs comprises numerous
hot springs, bubbling mud pools and fumaroles (steam vents) in an area of strongly
hydrothermally altered clay-rich rock approximately 200 m x 100 m in size. Many
fumaroles have temperatures 100°C or hotter, and temperatures of up to 172°C have
been recorded. Numerous studies have been carried out over the past 50 years to
investigate the geothermal energy potential of Sulphur Springs, to date, however,
no attempt at exploitation has been made.
Sulphur Springs geothermal field. The constant emission of steam does not serve as a "safety valve" for the volcano.
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Scientists collecting gas samples at a geothermal field. Changes in gas chemistry may indicate unusual activity at the volcano.
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Geothermal systems such as Sulphur Springs form when rainwater seeps into the ground
where it is heated by hot rock. The hot water becomes buoyant, and rises back to
the surface along cracks. In some places the water is heated so much that it rises
as steam. The heat source for the Sulphur Springs geothermal system is probably
the cooling magma body responsible for the young volcanism of the Soufrière Volcanic
Centre. The diagram below illustrates this process.
Formation of geothermal systems
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Currently, activity at Sulphur Springs is concentrated on the western side of the
Sulphur Springs Road. However, extensive areas of hydrothermally altered ground
together with stunted vegetation on the eastern side of the road (i.e. on the flanks
of Terre Blanche) clearly show that this area was once active. Furthermore, the
area beneath the viewing platform, including Gabriel’s crater, does not appear on
a map of Sulphur Springs from the 1950s (Robson and Willmore 1955), indicating that
this area of activity is relatively recent. It is possible that, over time, activity
at Sulphur Springs might continue migrating to the south and west.
Such migration of activity in geothermal systems such as Sulphur Springs is quite
normal. The area should, however, be watched closely for signs of further migration,
as this may have a significant long-term impact on nearby residences and structures,
such as the viewing platform. Migrating geothermal activity into areas of steep
slopes may also increase the likelihood of landslides triggered by extensive hydrothermal
alteration. Any significant changes in the geothermal
features at Sulphur Springs
should be reported to the National Emergency Management Organisation (NEMO) and/or
the Seismic Research Unit.
There are several misconceptions regarding Sulphur Springs. For details on these
go to the Frequently Asked Questions section.
Hazards from Sulphur Springs
Scientists believe there is only a very slim chance of a magmatic eruption
from the SVC in the next 100 years. However, there are serious ever-present hazards
at Sulphur Springs of which visitors should be aware.
Hot geothermal systems such as Sulphur Springs, emit large amounts of harmful gases.
Two of the more dangerous gases are carbon dioxide and hydrogen sulphide. Breathing
air with greater than 20% carbon dioxide can cause death. The gas is heavier than
air and tends to accumulate in hollows in the ground, displacing the breathable
air. Since it is colourless and odourless, people and animals are unable to notice
that it is there and may suffocate. In areas of hot or cold soufriere people should
not enter low-lying hollows to remove dead animals in case there is a buildup of
carbon dioxide.
Hydrogen sulphide has a very strong and unpleasant smell, like rotten eggs. It is
extremely toxic. Breathing low concentrations causes headaches, fatigue, dizziness,
and irritation of the eyes and upper respiratory tract. Inhalation of hydrogen sulphide
can seriously aggravate sinus and respiratory systems and can cause bronchitis.
Other dangers at Sulphur Springs include landslides, boiling pools, and phreatic
(steam) eruptions.
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