Download Frequently Asked Questions on Seismic and Volcanic Hazards in

 Frequently Asked Questions on Seismic and Volcanic Hazards in Dominica Why have we been having so many
earthquakes in northern Dominica recently?
Small earthquakes may be a sign of
volcanic unrest. They may be also lead up
to a larger earthquake or follow major
earthquakes such as the 29th November
2007
magnitude
7.3
Martinique
earthquake that occurred about 60 km to
the south of the current activity. However
the earthquakes do occur near to the
Morne
aux
Diables
volcano,
a
geologically young volcano in the north of
the island. Scientists are continuing to
analyse the earthquake data to better
understand the cause of the earthquakes.
What is the difference between volcanic
earthquakes and tectonic earthquakes?
Volcanic earthquakes are caused by the
movement of magma while tectonic
earthquakes are caused by the movement
of tectonic plates (huge slabs of rock that
make up the Earth’s crust).
Volcanic earthquakes occur as magma
makes its way to the surface of the Earth,
rising through the crust and breaking apart
the surrounding rock. Tectonic earthquakes
are caused by suddenly released energy
which has accumulated within the area
where plates meet.
Can an earthquake trigger a volcanic
eruption?
Yes. Large tectonic earthquakes can
"shake" a volcano and potentially trigger
an
eruption.
Alternatively,
tectonic
earthquakes can also stop a volcano that is
already erupting.
Should I be concerned about the recent
earthquakes we have been experiencing?
Yes, residents should ALWAYS be
concerned about seismic activity in
Dominica since it is located in the Lesser
Antilles, a subduction zone, which
generates earthquakes and volcanic
eruptions. Dominica will continue to
experience earthquakes and its volcanoes
will continue to be restless, therefore,
residents should ensure that they know how
to protect themselves during earthquakes.
Can volcanic activity in the northern part of
Dominica cause an eruption of the
volcanoes in the south of the island?
This is unlikely. Volcanoes close to each
other belong to a large system. It is the
changes within the overall system that lead
to eruptions, sometimes manifested at more
than one volcano. It would, therefore, be
incorrect to describe one eruption as being
the cause.
Can eruptions occur without warning and
destroy the entire island?
This is very unlikely. Volcanic eruptions in
the Eastern Caribbean are usually
preceded by recognizable symptoms, such
as small earthquakes, changes in gas
chemistry, and/or ground deformation
(swelling of the mountain) long before an
eruption occurs.
The UWI Seismic Research Centre
operates a monitoring system which should
enable scientists to provide sufficient
warning to the authorities prior to an
eruption so that appropriate action can be
taken.
Frequently Asked Question on Seismic Hazards in Dominica ‐ November 2009 UWI, Seismic Research Centre, St. Augustine, Trinidad & Tobago W.I. Phone: +1(868) 662‐4659 Fax: +1(868) 663‐9293 Website: www.uwiseismic.com Are all the volcanoes in the Caribbean
connected so that an erupting volcano on
one island will trigger the others nearby?
No, volcanoes in the Caribbean are not
connected and an eruption on one island
is unlikely to trigger an eruption on another.
When was the last volcanic eruption of
Morne aux Diables Volcano?
There have been no reports of historical
eruptions from Morne aux Diables.
However, research studies have dated
deposits from this volcano indicating
eruptions around 40 thousand years ago.
So how do scientists know that it is still
‘live’ or potentially active?
Morne aux Diables is still considered active
(i.e. ‘live’) because scientists continue to
detect signs of life such as occasional
volcanic earthquakes and the release of
volcanic gases around the volcano.
If Morne aux Diables were to erupt which
areas would be affected?
The entire area around the volcanic flanks
in the northern region of Dominica would
possibly be affected. This includes
Portsmouth, Savane Paille, Clifton, Penville,
Vieille Case and Hiroula Bay. A more
violent eruption could also affect Glanvillia,
Thibaud, Dos D’ane and La Source.
If a volcanic eruption eventually occurred
how long will it last?
The duration of volcanic eruptions in the
Caribbean varies considerably from a few
months (e.g. Soufrière Volcano St. Vincent,
1979) to many years (e.g. the current
Soufrière Hills eruption in Montserrat). The
average duration for a dome-forming
Caribbean-style volcanic eruption is around
2½ years.
Can earthquakes and volcanoes cause
tsunamis?
Yes, but tsunamis generated by volcanic
eruptions do not occur frequently and not
all earthquakes cause tsunamis. If you are
at the beach and you feel a strong
earthquake, however, you should move
immediately inland or to higher ground as
a tsunami may have been generated. How likely is it that a landslide from Morne
aux Diables could trigger a tsunami?
It is difficult to say but it is certainly less
likely than the possibility of a large and
potentially damaging earthquake occurring
near to the north coast of Dominica.
Where can I get more information?
Contact
the
Office
of
Disaster
Management at 448-7777 or visit the
UWI Seismic Research Centre’s web site at
www.uwiseismic.com for updates and
safety information.
Frequently Asked Question on Seismic Hazards in Dominica ‐ November 2009 UWI, Seismic Research Centre, St. Augustine, Trinidad & Tobago W.I. Phone: +1(868) 662‐4659 Fax: +1(868) 663‐9293 Website: www.uwiseismic.com