Caribbean at risk of tsunami
April 23rd, 2009
Detailed view of the c. 1 million tonne block, being undercut by wave erosion, on the northern margin of Morne aux Diables volcano. Tension cracks on the inland side of the block are clearly visible.
Up to 30,000 residents and tourists could be under threat from a newly discovered tsunami risk in the Caribbean, according to experts in disaster risk management.
The heavily populated coast of Guadeloupe will have little warning if a tsunami is
triggered by the collapse of a volcano on the nearby island of Dominica.
A team of geologists, led by Dr Richard Teeuw from the University of
Portsmouth, have discovered that a flank of the volcano Morne aux Diables
("Devils' Peak") shows signs of collapse and if so, a million-ton chunk of rock
could crash into the sea, producing tsunami waves up to almost 3 metres (10
feet) high.
Such a rock fall could also weaken three million tones of
rock upslope, potentially resulting in much larger landslides and waves of up to
five metres.
Dr Teeuw said: “It’s not a case of if this landslide
and tsunami will happen, but when. The trigger will probably be a major
earthquake, occurring after the heavy rain and coastal erosion of the hurricane season. It could happen in a hundred years or it
could happen next week.
“Guadeloupe is a densely populated island
with popular tourist beaches, many of which are wide with low angle gradients,
which leads to ‘tsunami run-up’ and increased wave heights. In places, there is
no protection from coral reef which otherwise might absorb some of the tsunami
wave
energy.
“There would be damage to property and if people were on the
beach then there could be loss of life. This part of the world is
well-prepared for hurricane hazards, but is relatively unprepared for the rapid
impact of a tsunami.”
The vulnerable area of rock was left exposed
several thousand years ago when the flank of the volcano collapsed into the sea.
Dr Teeuw will study the seabed for evidence of an ancient tsunami next year.
Since the original collapse, coastal erosion has undercut cliffs along the
over-steepened margin of the volcano, leaving the remaining flank of the volcano
unstable.
Dr Teeuw and colleagues made their discovery after
carrying out geomorphological surveys backed up by 3-D images from Google Earth
which show clearly visible tension cracks. The results convinced them that they
were looking at a serious landslide and tsunami hazard.
The
Guadeloupe archipelago is about 50 kilometres north of Dominica and tsunami
waves would hit its shores within minutes of the volcano’s collapse, giving
little chance to warn people on the coast.
The
island of Dominica has the highest concentrations of potentially active
volcanoes in the world. The area is regularly exposed to hurricanes and
occasional severe seismic activity.
Dr Teeuw and his team of students
and geoscientists will return to Dominica this summer, part-funded by the Royal
Geographical Society, for further geomorphological surveys, to better understand
the probable size of the various landslide zones on the flanks of Morne aux
Diable.
A further survey is planned for 2010, when the seafloor
along the margin of the volcano will be examined, allowing better estimates of
the likely tsunami hazard. Examining the age of the sediment on the seabed will
also help to determine when past coastal landslides occurred.
Dr Teeuw said: “The earthquake associated with the ancient
flank-collapse of Morne aux Diables volcano was probably much larger than any
experienced around Dominica in historical times. If so, that has serious
implications, raising the possibility of rare, but catastrophic, tsunami waves
in the Caribbean region.”
Dr Teeuw wants to raise awareness about
potential tsunami hazards to emergency planners, disaster managers and the
people of Guadeloupe and Dominica to help reduce their vulnerability and the
risk of disaster.
He made the discovery while supervising student
research projects around Morne aux Diables volcano and his work,
published in the newsletter of the American Geophysical Union (Eos, 90 (10),
81-82).
Source: University of Portsmouth
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