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Tsunamis
of Volcanic Origin in the Lesser Antilles Islands of the Caribbean
George Pararas-Carayannis
Excerpts
from presentation at the 2004 National Science Foundation Tsunami
Workshop in San Juan, Puerto Rico , from other papers published
in the Journal of Tsunami Hazards, http://www.STHJOURNAL.ORG
and from
other publications and review of the literature.
 INTRODUCTION
Earthquakes, volcanic
eruptions, volcanic island flank failures and underwater slides
have generated numerous destructive tsunamis in the Caribbean
region. Convergent, compressional and collisional tectonic activity
caused primarily from the eastward movement of the Caribbean
Plate in relation to the North American, Atlantic and South American
Plates, is responsible for zones of subduction in the region,
the formation of island arcs and the evolution of particular
volcanic centers on the overlying plate. The inter-plate tectonic
interaction and deformation along these marginal boundaries result
in moderate seismic and volcanic events that can generate tsunamis
by a number of different mechanisms.
The active geo-dynamic
processes have created the Lesser Antilles, an arc of small islands
with volcanoes characterized by both effusive and explosive activity.
Eruption mechanisms of these Caribbean volcanoes are complex
and often anomalous. Collapses of lava domes often precede major
eruptions, which may vary in intensity from Strombolian to Plinian.
Locally catastrophic, short-period tsunami-like waves can be
generated directly by lateral, direct or channelized volcanic
blast episodes, or in combination with collateral air pressure
perturbations, nuess ardentes, pyroclastic flows, lahars, or
cascading debris avalanches. Submarine volcanic caldera collapses
can also generate local destructive tsunami waves.
Volcanoes of the
Eastern Caribbean Island Arc (Web graphic of West Indies University)
Volcanoes in the Eastern
Caribbean Region have unstable flanks. Destructive local tsunamis
may be also generated from aerial and submarine volcanic edifice
mass edifice flank failures, which may be triggered by volcanic
episodes, lava dome collapses, or simply by gravitational instabilities.
The following brief report describes recent volcanic episodes
in the Eastern Caribbean and the tsunami or the tsunami-like
waves which were generated. More specifically, the report reviewa
recent volcanic eruptions of the Soufriere Hills volcano on Montserrat,
of Mt. Pelée on Martinique, of Soufriere on St. Vincent
and of the Kick'em Jenny underwater volcano near Grenada.
RECENT
TSUNAMIS OF VOLCANIC ORIGIN IN THE LESSER ANTILLES REGION
In recent times, Soufriere
Hills on Montserrat, Kick'em Jenny near Grenada, Soufriere of
St. Vincent, and Mt. Pelée on Martinique, are volcanoes
in the Lesser Antilles region that have generated local tsunamis
by renewed volcanic activity and associated flank failures and
landslides (Lander et al 2002). Given the degree of violent volcanic
activity and the flank instabilities of stratovolcanoes in the
region, it is believed that the occurrences of tsunami waves
have been under-reported in historical records, probably because
the effects of such sea level disturbances were either localized
or were overshadowed by greater catastrophes caused by violent
volcanic eruptions The following is a brief overview of some
of the reported historical tsunami events.
Montserrat
Island Tsunamis 
The recent historic
record documents several tsunamis at Montserrat Island. Earthquakes
in the area generated some of these, while others were generated
by pyroclastic flows of the Soufriere Hills stratovolcano, by
debris avalanches, and by major flank failures and landslides.
Also, the coastal geomorphology of the eastern part of Montserrat
near the Chance Peak of the Soufriere Hills volcano indicates
that massive landslides must generated local tsunamis in the
distant past. According to the more recent historic record, an
earthquake in the region on September 13, 1824, resulted in a
remarkable rise and fall of sea level at Plymouth. Another major
earthquake near Antigua, reportedly triggered landslides into
the sea in Antigua, Montserrat and Nevis Islands. However, most
of the noteworthy tsunamis were generated recently as a result
of renewed activity of the Soufriere Hills volcano.
Debris avalanches
and pyroclastic (lava) flows associated with the 1999 eruption
of the Soufriere Hills volcano on the island of Montserrat reached
the sea and generated a tsunami. (Photo: Montserrat Volcanic
Observatory)
 On December 26, 1997, following
a major eruption of Soufriere Hills a landslide - assisted by
pyroclastic flows - reached the sea along the southwestern coast
of the island and generated significant tsunami waves. (Heinrich
et al., 1998, 1999a,b, 2001). Maximum runup of the waves, about
ten kilometers away from the source region, was about 3m, with
inland inundation of about 80 meters. Similar debris avalanches
and pyroclastic flows associated with a 1999 eruption of Soufriere
Hills reached the sea and generated another local tsunami. The
height of the waves in the immediate area ranged from12m
but attenuated rapidly. By the time they reached the islands
of Guadeloupe and Antigua the maximum runup heights were only
about 50 cm. The most recent tsunami occurred on July 12, 2003,
following a major collapse of a lava dome (Pelinovsky et al 2004).
A pyroclastic flow reached the sea and generated a tsunami, which
was reported to be about 4 meters on Montserrat and about 0.5-1
m at Guadeloupe.
Travel time chart
of the tsunami generated by the 1999 debris avalanche at Montserrat
Island.
Pyroclastic flow
from the 2003 eruption of Soufriere Hills volcano on Montserrat
reaching the sea.("Copyright Montserrat Volcano Observatory/Government
of Montserrat and British Geological Survey; photo used by permission
of the Director, MVO")
Martinique
Island Tsunamis
  Mt Pelée on Martinique
is another active stratovolcano with unstable flanks composed
primarily of pyroclastic rocks. As such, it must have generated
numerous tsunamis in the distant geologic past. The first reported
violent eruption of Mt Pelée occurred in 1792. The record
does not indicate whether the eruptions caused flank failures
on the island or generated tsunamis. Such events could have occurred
but not reported. Even the recent historic record is unclear.
For example, there are reports of observed sea level agitations
on Martinique in 1767, but it is not known whether these were
tsunami waves generated by a distant earthquake or an island
flank failure.
Mt. Pelée's
eruption of May 8, 1902 killed 29,000 people and destroyed the
city of St. Pierre. Local destructive tsunamis were triggered
by a lahar, a nuée ardente nuee and by flank failures.
(Photograph by Heilprin taken on May 26, 1902)
Devastation of
the town of St. Pierre on Martinique Island by a Nuee Ardente
of the 1902 eruption of Mt. Pelée. (Photograph by Heilprin,
1902).
On 30 November 1823
an earthquake in the area generated a tsunami, which caused damage
to St. Pierre Harbor. In 1824, another earthquake near St. Pierre
was probably responsible for a very "high tide" that
reportedly grounded several ships in the harbor.
In the spring of 1902,
Mt Pelée began erupting again. According to historic records,
as the summit eruptions intensified, the water of the Etang Sec
crater lake heated to near boiling point. On May 5, the crater
rim broke, and extremely hot water cascaded down River Blanche.
The hot water, mixed
with loose pyroclastic debris and mud, formed a massive 35-meter
high lahar that reached a speed of about 100 kilometers
per hour. The hot volcanic mudflow buried everything in its path.
Near the mouth of River Blanche, north of St. Pierre, it hit
a rum distillery and killed 23 workers. The lahar continued into
the sea, where it generated 4-5 meter tsunami waves, which flooded
the low-lying areas along the waterfront of St. Pierre. Subsequently,
on May 8, 1902, a catastrophic nuée ardente cascaded for
about 6 km down-slope from the central crater of the volcano,
at a velocity of more than 140 Km per hour, destroying completely
St. Pierre, and killing 29,000 of its inhabitants. According
to the historic record there were only two survivors one
in a prison dungeon. There is not much information on the tsunami
that the nuée ardente must have generated, as the immensity
of St. Pierre's destruction overshadowed everything else.
St. Vincent
Island Tsunamis
There is not much
information about tsunamis generated from eruptions or flank
failures of the Soufriere volcano on St. Vincent Island, although
several must have occurred. The historic record shows that the
volcano erupted violently in1718, 1812, 1902, 1971-1972 and in
1979. The 1902 eruption was the most catastrophic and killed
1,600 people. The record shows that, on May 7, 1902, a day before
the most violent eruption of Mt Pelée on Martinique, tsunami
like disturbances of up to 1 meter were reported for the harbors
of Grenada, Barbados and Saint Lucia. Although the origin of
these waves is not known with certainty, the most likely source
could have been pyroclastic flows reaching the sea from the violent
eruption of Soufriere volcano on St. Vincent. Alternatively,
the sea level disturbances could have been generated by an unreported
flank failure of Mt Pelée, which was also erupting at
that time. The historic record documents that on May 7, 1902
the submarine communication cables from Martinique to the outside
world were cut.
Grenada
Island Tsunamis
 Kick'em Jenny is an active and
growing submarine volcano about 8 km off the North side of the
island of Grenada, which erupted frequently during the 20th Century
(Smithsonian Institution, 1999). There have been several local
tsunamis generated by these eruptions. The volcano's first recorded
eruption reportedly occurred in 1939, but undoubtedly there were
many unreported occurrences before that date. Since 1939 there
have been at least ten more eruptions. The better known are those
that occurred in 1943, 1953, 1965, 1966, 1972 and 1974. The 1974
eruption was major. The last known major eruption occurred in
1990.
Volcanoes of Grenada
(USGS graphic)
The 1939 and 1974
eruptions ejected columns above the sea surface. At the peak
of the July 24, 1939 eruption - which lasted more than 24 hours
- a cloud rose 275 meters above the sea surface (Tilling, 1985;
Seismic Research Unit Website, Univ. of West Indies, 2001). The
event was witnessed by a large number of people in northern Grenada.
Kick'em Jenny's 1939 eruption also generated a series of tsunami-like
waves, which had amplitudes of about 2 meters in northern Grenada
and the southern Grenadines. The waves probably reached the west
coast of the Barbados, but were not noticed as their heights
had attenuated significantly.
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