ISLAND PROFILES
Grenada - Kick `Em Jenny Hazards
Kick 'em Jenny is the source of a number of potential dangers. The most immediate
and frequent danger is to marine vessels in the vicinity of the volcano during eruptions
and during the 'quiet' periods between eruptions. The volcano lies directly beneath
one of the main inter-island shipping routes and the area is popular both with recreational
sailors and fishermen. For this reason Kick 'em Jenny is carefully monitored and
a 1.5km exclusion zone around the summit of the volcano is currently in place. Although
scientists continue to stress the improbability of an eruption generating a tsunami
(a giant sea wave) this hazard also remains of great public concern.
Ballistic Projectiles
If Kick 'em Jenny erupts, it might throw hot rocks up through the water
column into the air above the surface of the sea. Such rocks could travel as far
as 5km from the volcano, and would pose a great danger to nearby ships or boats.
Any ship which happened to be over the vent of Kick 'em Jenny during the
1939 eruption
would certainly have been destroyed.
In September 1952 a Japanese research ship was passing over the active Myojinsho
volcano in the Pacific Ocean south of Japan when that volcano erupted ripping the
hull apart. All 31 people on board were killed. This volcano is similar to Kick
'em Jenny but of a slightly less violent type.
This picture shows an eruption from a submarine vent off the south coast of Iceland in 1963 which eventually led to the formation of Surtsey Island. This picture closely resembles the description of the 1939 eruption of Kick 'em Jenny. An eruption such as this one would present a clear hazard to shipping.
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Lowered Water Density
Submarine volcanoes release large quantities of gas bubbles into the water,
even in quiet times between eruptions. This can lower the density of the seawater
above the vent. This is very dangerous to shipping, because boats entering a zone
of lowered water density will lose buoyancy and may sink.
Tragedy of the Island Queen
One of Grenada's worst maritme tragedies may have resulted from just this
phenomenon. On the 5th August 1944, the wooden schooner Island Queen, with over
60 people on board, disappeared between Grenada and St. Vincent. At the time it
was thought that a German or allied submarine had torpedoed the boat. These theories,
however, cannot easily explain the total lack of debris after the boat's disappearance.
However, if a boat sinks because of lowered water density everything would sink.
Kick 'em Jenny had, in fact erupted the year before (1943) and it is highly likely
that it was still actively degassing in 1944, without any signs at the sea surface
of such activity.
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A degassing submarine volcano can lower the
water density above the volcano. This possibility
of lowered water density above the volcano is an
ever-present hidden hazard.
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Tsunamis
In addition to the vulnerability of the shipping industry many people are also concerned
about sea waves or tsunamis. While it is probable that large explosions or landslides
at Kick 'em Jenny could generate tsunamis, the threat from tsunamis has been largely
over exaggerated. Not all eruptions at Kick 'em Jenny will generate tsunamis and
not all tsunamis will be large.
Studies show that the worst eruption that Kick 'em Jenny is capable of under any
circumstances might generate a wave with an amplitude of 10m in open waters at a
distance of 10km from the vent. Waves of this amplitude could be generated only
if the volcano began to erupt in water depths of less than about 130m. Currently
the depth to the vent is 268m.
Prior to recent bathymetric measurements it was thought that Kick 'em Jenny was
growing steadily towards the surface and thus approaching depths at which previous
workers (e.g. Smith and Shepherd 1996) had suggested that eruptions could become
more explosive. Thus in addition to direct hazards caused by volcanic activity,
such as water disruptions and ballistic projectiles over the volcano, there was
some speculation that the probability of an eruption-generated tsunami was increasing.
However, with the re-evaluation of previous surveys showing clearly that the volcano
is not growing towards the surface, together with the results of the most-recent
survey which revealed that the vent region of the volcano (the crater floor) is
268m below sea level, the likelihood of a tsunamigenic explosive eruption is now
considerably lower (see figure below). Eruption-generated tsunamis may, of course,
become a more significant hazard if Kick 'em Jenny does begin to grow closer to
the surface.
The best-studied example of underwater dome growth in the West Indies occurred at
the Soufriere volcano in St. Vincent in 1971. On that occasion a dome began to grow
at the bottom of the 175 metre deep crater lake in early October 1971 and reached
the surface in late September. By analogy with this episode we would expect a period
of one to two months of steady eruption before Kick 'em Jenny grows into the violently
explosive range of depths.
For a detailed study of the potential effects of eruptions of Kick 'em Jenny, particularly
its potential for generating tsunamis, go to the bibliography section of this site.
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This figure shows that Kick 'em Jenny would need to grow a considerable amount (approximately 138m) before it could potentially produce explosive eruptions which may trigger tsunamis. Scientists do not know how long this growth could take.
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