Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters - by Dr. George Pararas Carayannis

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Eruptive Processes of Stratovolcanoes of the Lesser Antilles (Islands of Montserrat, Martinique, St. Vincent and Grenada) - Mechanisms of Flank Failures and Tsunami Generation

George Pararas-Carayannis

Excerpts from presentation at the 2004 National Science Foundation Tsunami Workshop in San Juan, Puerto Rico , and from recent paper published in the Journal of Tsunami Hazards, Volume 22, Number 2. 2004 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 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 also triggered earth tides, earthquakes, or simply by gravitational instabilities. Mechanisms, resulting in flank failure processes of volcanoes and their potential for tsunami generation - in general - were presented separately. More specifically, the following report evaluates recent volcanic eruption mechanisms of active stratovolcanoes of the Lesser Antilles in the Eastern Caribbean. Specifically discussed and analyzed are the eruptive processes at work for Soufriere Hills, Mt. Pelée, Soufriere and Kick'em-Jenny, as well as the time history of major specific eruptions that resulted directly or indirectly in tsunami generation in recent times.

Eruptive Processes of Stratovolcanoes of the Lesser Antilles Islands (Montserrat, Martinique, St. Vincent and Grenada) - Mechanisms of Flank Failures and Tsunami Generation

 

Soufriere Hills Volcano on Montserrat Island

The Soufriere Hills, located on the southern part of Montserrat Island, is a very active, primarily andesitic stratovolcano (Rowley1978), which is the predominant type of explosive volcano in the world. Its present elevation is 915 m. The first known historical eruption was in 1995. Since then there have been several more eruptions in the late 1990s (Hooper and Mattioli, 2001). The volcano is presently very active. All of its eruptions have been associated with earthquake swarms , lava dome collapses, steam explosions, ash falls, pyroclastic flows and debris avalanches.

The volcano's flank instability and its potential for landslides and tsunami generation result from the composition of its magma which is very sticky and has a high content of dissolved water. In fact, eruptions appear to be linked with rainstorms and high earth tides. When the volcano erupts it tends to form a steeply sloped peak made of alternating layers of lava, block, and ash. Thus, the slopes of the volcano become unstable and susceptible to massive landslides and debris avalanches, some of which can reach the sea and generate local tsunamis. In fact several have occurred in the last few years.

Eruptive Processes of the Soufriere Hills Volcano: To understand better the tsunamigenic potential of the Soufriere Hills volcano on Montserrat, we must review further its eruptive processes. Two types of eruptive mechanisms characterize this volcano, both of which have the potential to generate local tsunamis. In both cases, magma inside the volcano is driven up by buoyancy and gas pressure, which may vary depending on its viscosity.

In one type of eruption, the volcano will explode and shoot molten rock violently into the air in the form of dense clouds of lava fragments. The larger and heavier fragments tend to fall back around the volcanic vent which may become increasingly unstable as the eruption progresses. Often, the accumulation may run down slope as ash flows, while some of the finer particles may be carried by the wind. Often, both ash and pyroclastic flows can trigger debris avalanches and larger landslides and slope failures on the volcano ( DeGraff,1988) that can generate small local tsunamis.

In the second type of eruption, the molten rock - which is lighter than the surrounding solid rock - breaks through the weaker stratigraphic layers and raises closer to the surface forming a lava dome. When the dome becomes too steep, or if pressure within builds up, it collapses and disintegrates, spewing lava and hot ash down the side of the volcano. Also, it may form a mushroom cloud of ash that can spread over the island. The collapse of such lava domes releases pressure and frequently causes subsequent massive eruptions that can also affect the volcano's flank stability, thus generating pyroclastic flows, debris avalanches, landslides and massive flank failures. In fact a combination of the above-described eruptive processes occurred during eruptions in the summer of 1995. Specifically, on July 18, 1995, Soufriere Hills had its first recorded eruption in historic times. It begun with a small phreatic eruption. Periods of intense seismic activity were associated with ejection of steam and ash, shortly after a new vent opened southwest of an old volcanic dome known as Castle Peak. The eruption culminated into a major event on August 21, 1995, when the volcano begun spouting molten ash, rock, and gas over the island, killing 19 and incinerating the capital city of Plymouth. A strong burst of steam carried a cloud of ash to an altitude of 7,000 feet. The eruption triggered several landslides that reached the sea, but there was no report of any unusual waves being generated (Mangeney et al. 1998; Calder et al. 1998).

The Eruption and Tsunamis of 26 December 1997 and 1999 and 2003: As already mentioned, the Soufriere Hills volcano either erupts by exploding and expeling lava or by dome collapse. Both types of eruption can be destructive as they can produce dangerous ash hurricanes and pyroclastic flows, trigger landslides and debris avalanches and thus generate tsunamis. Although the 1995 eruption and other volcanic processes that occurred subsequently did not generate a tsunami, apparently they weakened Soufriere Hills' flanks. This weakness contributed to the subsequent volcanic flank failures associated with the eruptions of 1997, 1999 and 2003 ­ which generated tsunamis.

Specifically, on June 25, 1997, after two years of precursory swelling and micro earthquake activity, Soufriere Hills volcano erupted again. A damaging pyroclastic flow of ash, gas, and rock killed at least ten people and destroyed nine villages. A lava dome was subsequently observed which built up steadily in the volcano's crater for over two months. On 26 December 1997, following the collapse of this lava dome, a major eruption occurred. The eruption generated ash hurricanes, which destroyed Plymouth. Both the ash hurricanes and a landslide - possibly assisted by pyroclastic flows triggered by the dome-collapse - reached the sea, along the southwestern coast of the island and generated significant tsunami waves (Heinrich et al., 1998, 1999a,b, 2001). The maximum runup of the waves was about 3m. about ten kilometers away from the source region, with inland penetration of about 80 meters. The volume of the landslide debris, which generated this tsunami, was estimated to be about 60 million cubic meters (Lander et al., 2003).

Similar debris avalanches and pyroclastic flows associated with the1999 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 the waves reached the islands of Guadeloupe and Antigua their heights attenuated considerably. Maximum runup heights were only about 50 cm.

The most recent tsunami was produced by the eruption of July 12, 2003 (local date) following a major collapse of a lava dome (Pelinovsky et al 2004; Young 2004). Pyroclastic flows and a debris avalanche reached the sea at the end of Tar River Valley on the east coast and generated this tsunami, which was reported to be about 4 meters at Spanish Point on Montserrat Island and about 0.5-1 m at Deshaies and near Plage de la Perle on Guadeloupe where it caused some damage to fishing boats.

Map of the Island of Vulcano in Italy where a 200,000 cubic meter massive flank failure on the northeast side generated local tsunami (after Imbo,1965 and Keller,1980)

In support that debris avalanches and extensive landslides of andesitic volcanoes will only generate local destructive tsunamis, is supported by the April 20, 1988 massive flank failure of the northeast flank of the volcano La Fossa on the Island of Volcano in the southern Tyrrhenian Sea, in Italy. According to modeling studies - which were based on photogrammetric techniques conducted in 1981 and 1991 - the large 1988 flank failure of La Fossa involved a mass with a volume estimated to be about 200,000 cubic meters. The mass that was detached fell into the sea for about 10 seconds. A small tsunami was generated in the bay between Point Nere and Point Luccia on the island. Maximum observed runup height of the waves was about 5.5 meters at Porto di Levante and presumably even at Monterosa on Lipari Island (Barberi, et al 1990; Lander et al. 2003).

Mt. Pelée Volcano on Martinique Island

Mt. Pelée on Martinique is a very active island-arc stratovolcano with unstable flanks made mostly of pyroclastic rocks (Smith and Roobol 1990). Its summit elevation is 1397 m. It undergoes similar eruptive processes as other Caribbean volcanoes and can also generate destructive local tsunamis by pyroclastic flows, flank failures or debris avalanches. However, what makes Mt. Pelée unique has been its unusual lava dome formations, the intensity and styles of its eruptions and the unusual and violent pyroclastic flows it can generate (Fisher and Heiken1982). The volcano has a long history of eruptions in the last 5,000 years (Westercamp and Traineau 1983). In more recent historic times the volcano erupted in 1635, 1792, in 1851-1852, in 1902- 1905 (Heilprin 1908) and in 1929-1932 (Perret 1937).

The historic record documents two extremely violent eruptions in 1792 and in 1902 - associated with numerous other phenomena that followed dome collapses ­ and by which local tsunamis were generated. The eruptive processes of Mt. Pelée and the tsunami generation mechanisms that are described in subsequent sections are based on what occurred on Martinique in May of 1992 and whatever little is known about the violent volcanic eruption of 1792.

Eruption Processes of Mt. Pelée - Eruptions of Mt. Pelée range in volcanic explosivity intensity from severe Vulcanian (VEI = 3) - which can occur yearly - to cataclysmic Vulcanian-Plinian events (VEI = 4) separated in time by many decades. The Peléeean eruptions - as they are now termed because of their unique characteristics - are extremely violent eruption events that often include collapses of ash columns, and unique pyroclastic flows known as "nuées ardentes" - a type of pyroclastic avalanche mixture of gas, dust, ash and other hot glowing incandescent solid particles and lava fragments - and debris avalanches containing large amounts of ignimbrites (ash flow tuffs). These unusual pyroclastic flows are usually triggered after a lava dome collapse.

The 1902 Eruption of Mt. Pelée on the island of Martinique. The destruction of the town of St. Pierre was caused by a nuée ardente. (Photograph by Heilprin, 1902).

The Eruption and Tsunamis of May 1902 ­ A previously stated, an extremely violent volcanic eruption occurred on Mt. Pelée in 1792. It is very probable that a tsunami was generated at that time as a result of a flank failure or pyroclastic flow, but there are no reports documenting it. However, the 1902 eruption and its associated unusual phenomena are well documented in the literature (Lacroix, 1904; Heilprin 1908; Fisher et al 1980). The May 1902 tsunamis were generated by a lahar and a subsequent nuée ardente of a violent eruptive phase.

In early 1902, a large dome of very viscous lava had grown on Mt. Pelée's flank near its summit, largely by expansion from within. As the lava dome grew, its outer surface cooled and hardened. There is not much information on the size of this particular lava dome, but it could have been as big as that of the Katmai volcano in Alaska, which collapsed and triggered an eruption in 1912. That dome had been circular and measured about 250 meters across and 60 meters in height. However, what was reported about Mt. Pelée's lava dome is that it had cut a large V-shaped notch through the cliffs that surrounded the volcano's summit crater. According to reports, the "notch was like a colossal gun sight pointing directly at the town of St. Pierre".

According to historic records, on May 5, 1902, a 35-meter lahar cascaded down the flank of the volcano and reached the sea. The lahar generated a local tsunami wave of about 4-5 meters in height, which killed one hundred people in St. Pierre. Subsequently, at approximately 7:50 a.m. on May 8, 1902, the pressure from within the volcano reached a critical level. Suddenly, the summit lava dome collapsed and shattered with a deafening roar, spilling loose fragments down-slope. The sudden release of pressure triggered by the dome collapse resulted in an extremely violent eruptive phase of Mt. Pelée.

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).

A large nuée ardente cascaded from the central crater for about 6 km down the south flank, at a velocity of more than 140 Km per hour. In less than one minute it struck the coastal town of St. Pierre, destroying it completely and killing 29,000 of its inhabitants. Only two people are known to have survived. According to reports (Heilprin 1908; Fisher et al 1980) the directional blast was so strong that it carried a three-ton statue sixteen meters from its mount. One-meter thick masonry walls were blown into rubble. "Supporting girders were mangled into twisted strands of metal". The heat of the nuée ardente nuee was immense and ignited huge fires. Thousands of barrels of rum that was stored in the city's warehouses exploded and burned in the streets.

There is not much direct information on the tsunami that the nuée ardente must have generated, as the immensity of St. Pierre's destruction overshadowed everything else. However, it was reported that the nuée ardente continued seaward toward the harbor where it destroyed at least twenty ships that were anchored offshore. The American sailing ship "Roraima", which had arrived only a few hours earlier, burned and all its crew and passengers perished. The steamship "Grappler" was presumably capsized by the force of the nuée ardente. However, it is more than likely that it was capsized by the wave the nuée ardente generated in the harbor.

Mechanisms of tsunami generation involving cascading volcanic gases and rapidly moving pyroclastics flows are not confined to Caribbean volcanoes or to Mt. Pelée, in particular. There is evidence that similar hot glowing avalanches of hot gas, dust, ash and pyroclastics have generated several tsunamis in the distant past in New Zealand and elsewhere around the world.

St. Vincent Island - La Soufrière Volcano

La Soufrière is an active and dangerous stratovolcano on the island of St. Vincent in the Windward Islands of the Caribbean, with a well-documented history of violent eruptions (Shepherd and Aspinall,1982). The present elevation of its summit is at 1220m. There is a lake within the summit crater. La Soufrière should not be confused with a volcano by the same name on the island of Guadaloupe.

The 1976 eruption of La Soufrière on St Vincent island (Photograph by Richard Fiske)

There evidence of activity on Soufrière for the last 650,000 years (Hay, 1959; Rowley1978). In recent times, major eruptions occurred in 1718, 1784,1812, 1814, 1880, 1902-03 (Anderson 1784; Anderson 1903; Flett 1902,1908; Anderson and Flett 1903; Sapper 1903; Anderson 1908, Carey and Sigurdsson 1978). In the twentieth century they were major eruptions, in 1971-72 (Aspinall et al 1972; Baker, 1972; Tomblin et al. 1972; Aspinall 1973; Aspinall et al 1973) and in 1979 (Shepherd et al 1979; Shepherd et al 1982; Barr and Heffter 1982; Brazier et al 1982; Fiske and. Sigurdsson. 1982; Graham and Thirlwall. 1981). The 1812 eruption resulted in many deaths. However, the 1902 eruption was the most catastrophic of all resulting in the loss of 1,600 lives.

Eruption Processes of Soufrière - Geologic evidence indicates that for the past 4,000 years the Soufrière volcano's eruptions have alternated between explosive episodes associated with the forceful ejection of fragmented material and pyroclastic flows to quiet effusion of slow moving lava that forms summit domes (Earle 1924; Hay 1959; Heath et al 1998). The 1979 eruption is typical of such variation. It begun quite suddenly with less than 24 hours of precursor activity. The mechanism of its subsequent explosive eruption has been well documented (Shepherd and Sigurdson 1982). The first eruptive episode was Vulcanian in character. It sent a plume of steam and tephra to a height of 20 km. and lasted a little less than two weeks (Sparks and Wilson 1982). The second episode consisted of a quiet extrusion and growth of a basaltic andesite lava dome (Huppert et al. 1982).

The Eruption and Tsunamis of May 7, 1902 - There is not much information about tsunamis generated from eruptions or flank failures of the Soufrière stratovolcano, although several must have occurred in the geologic past - and even more recently. The record shows that on May 7, 1902, a day before the most violent eruption of Mt Pelée on Martinique, tsunamis 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, the most likely source could have been air pressure waves from the violent eruption of Soufrière on that day, or pyroclastic flows and debris avalanches reaching the sea.

Coincidentally, the historic record also shows that on the same day - May 7, 1902 - the submarine communication cables from the island of Martinique to the outside world were cut. Whether these cables routed near St. Vincent Island is not known. The exact area where the cables failed is not known. Thus, it is difficult to determine what caused the cable failures and whether the sea level disturbances observed at the harbors of Grenada, Barbados and Saint Lucia had the same source. The waves could have been generated by an unknown flank failure of Mt Pelée, and the cable failures by an underwater debris avalanche. On May 5, Martinique had already experienced a destructive local tsunami generated by a lahar.

Island of Grenada - Kick'em Jenny Submarine Volcano

Kick'em Jenny is a growing submarine volcano about 8 km off the north side of the island of Grenada. It is the southernmost active volcano in the Lesser Antilles volcanic arc and has erupted frequently during the 20th Century (Smithsonian Institution, 1999). Presently, the volcano has a circular base of about 5000m, its main cone has reached a height of about 1300m above the sea floor, and its summit is only 160 m below the sea surface. The volcano is growing rapidly at a rate of approximately 4 meters per year. At this rate the volcano is expected to reach the surface and form an island in the near future ­ if there is no flank subsidence or cone collapse.

Kick'em Jenny's first recorded eruption occurred in 1939, but many unreported eruptions must have occurred prior to that date. Since 1939 there have been at least twelve or more events. Most of the historical eruptions were documented by acoustic measurements, since submarine volcanoes generate strong acoustic signals that are recorded by seismographs. Known eruptions occurred in 1939,1943, 1953, 1965, 1966, 1972, 1977, 1988, and in1990. The better-known events are those that occurred in 1943, 1953, 1965, 1966, 1972 and 1974. The last major eruption occurred in 1990. Earthquake swarms in late 2001 indicated renewed activity. The latest eruption occurred on March 15, 2003.

In 2003, during a survey of Kick 'em Jenny, an inactive underwater volcano was discovered about 3 km away. It is, now known by the name of Kick'em Jack. Its summit elevation is 190 m below the sea surface.

The Eruption and Tsunamis of 1939 and 1974: According to historical accounts and eyewitness reports from northern Grenada, the July 24, 1939 eruption of Kick'em Jenny was major and lasted for at least 24 hours. The eruption ejected a cloud plume above the sea surface. Furthermore at the peak of the eruption, the cloud plume rose 275 meters above the sea surface (Tilling, 1985; Univ. of West Indies, 2001). The eruption generated numerous tsunami-like waves of short period. These waves had maximum amplitudes of about 2 meters in northern Grenada and the southern Grenadines, but were almost imperceptible when they reached the west coast of the Barbados.

Eruption Processes of Kick'em-Jenny: The underwater topography of the sea floor north of Grenada indicates that Kick'em Jenny comprises of three small craters and two lava domes ­ all of which probably share the same magmatic chambers.

Two-minute topography of the sea floor north of the island of Grenada, showing the geomorphology of the calderas, cones and domes, generally known as the Kick'em Jenny volcano (web graphic)

As most of the Caribbean volcanoes, Kick'em Jenny has had both violent and effusive eruptive episodes. Eruptions of the volcano have been associated with magmas, which have ranged in compositions from basalt to basaltic andesitic. Thus, gently extruded submarine pillow lavas and domes as well as tephra and other pyroclastics from minor phreatomagmatic explosions, are present in submarine deposits around the volcano.

Flank instability: The distribution and orientation of pyroclastic deposits on the sea floor, primarily to the west side of Kick'em Jenny, indicate that many volcanic eruptions must have occurred that have been lateral or channelized blasts, possibly following the collapse of lava domes. Furthermore NOAA surveys in 2003 demonstrated the presence of deposits from a debris avalanche. The geomorphology of the sea floor indicates that this debris avalanche extends west for 15 km and perhaps as much as 30 km from the volcano, into the Grenada Basin (Sigurdsson et al 2004). Also, earlier multibeam surveys of the sea floor discovered the existence of an arcuate fault escarpment - of yet unknown age - to the east of the active cone. Because of its shape and length, this escarpment cannot be related to caldera subsidence and collapse. Its configuration and the overall geomorphology of the sea floor suggest that a larger scale subsidence or volcanic mass edifice collapse occurred in the distant past. It also suggests that Kick'em Jenny volcano might have been at or above sea level in the past.

Overall, the volcano's present rapid upward growth towards the surface of the sea is indicative of active vertical summit eruptions and the build up of a cone by deposition of pyroclastics. However, the flanks of this cone must be very unstable and subject to collapses and the generation of future debris avalanches, which could slow the volcano's, present rate of growth. Additionally, hydromagmatic explosions associated with future eruptions could also result in greater flank.

Bathymetry and distribution of volcanic deposits from eruptions of Kick'em Jenny volcano (Web graphic at http://volcano.und.edu/vwdocs/volc_images/north_america/kick.html)

instability and might also slow down the rate of growth. Future major eruptions can be expected to be more violent and to eject sizeable columns above the sea surface to heights much greater than those of the 1939 and 1974 events. Major future eruptions can be expected to have considerably higher plume clouds, because of the greater strength of hydromagmatic episodes as the summit approaches the sea surface and the inclusion of a higher content of molecular water ­ in the form of superheated steam - along with ejected tephra and other fine pyroclastic materials.

Assessment of the Tsunamigenic Potential of Future Eruptions of Kick'em Jenny:

The frequency of Kick'em Jenny's eruptions and the volcano's rapid growth toward the sea surface have raised concerns that future eruptions will generate tsunami waves with far reaching destructive effects on Caribbean islands and along the coast of Venezuela. Earthquake swarms in late 2001 added to concerns that Kick'em Jenny will again have a major eruption.

Although there is a good probability that several eruptions will occur in the near future ­ and in fact the latest occurred on March 15, 2003 - the potential tsunami risk from a future eruption has been highly exaggerated by the introduction of speculative and highly unrealistic "worst case" scenarios. Kick'em Jenny is not Krakatau and does not pose the purported potential tsunami danger that has been misreported by the media. Kick'em Jenny is a much smaller volcano than Krakatau and has much smaller crater dimensions and magmatic chambers. The tectonic interactions that have produced this volcanic center in the Caribbean are substantially different than those of Krakatau, which erupted in 1883 and generated a destructive tsunami, which killed nearly 37,000 people in Indonesia
(Pararas-Carayannis, 2003). Kick'em Jenny's magmatic geochemistry is substantially different. Its magma composition ranges from mainly basalt to basaltic andesite. At the present stage of its development, Kick'em Jenny volcano's small dimensions and geochemistry prevent eruptions of Vulcanian or Plinian intensity or extremely massive volcanic edifice collapses. The following is a realistic analysis of Kick'em Jenny's tsunamigenic potential and future risks.

Tsunami Generation from Submarine Explosive Eruptions: Even a major explosion at a peak phase of Kick'em Jenny's eruption would be expected to generate tsunami-like waves, not as a single event but spread over a period of 24 hours or more. The periods of these waves will be relatively short and will range from 1-4 minutes at the most. Because of the short periods and wavelengths, the wave heights will decay rapidly with distance. As in 1939, the waves from future eruptions will be of significance along the north coast of Grenada and along the western coasts of Isla de Ronde and Isla Calle (Grenadine Islands), and possibly Tobago, St. Vincent and Barbados, but not anywhere else in the Caribbean. This conclusion is further supported by the numerical modeling studies that were conducted at the Los Alamos National Laboratory (Gisler et al 2004). Specifically, numerical simulations of Kick-'em Jenny's explosions with the same 3-D compressible hydro code used for asteroid impacts - and injecting as much as 20 kilotons of thermal energy at the apex of Kick'em Jenny's volcanic cone, confirmed that only short period tsunami-like waves can be generated and that the waves will attenuate rapidly away from the source. Accordingly, it is concluded that explosive eruptions do not couple well to water waves. The waves that are generated from such eruptions are turbulent and highly dissipative, and don't propagate well.

At the present time, the depth of Kick'em Jenny's summit and the hydrostatic pressure above it dampen the energy of eruptive explosions - although both the 1939 and 1974 events were violent enough to break through the sea surface. As the volcano keeps on growing towards the surface, the hydrostatic column pressure above the eruptive vents will decrease significantly. Future eruptions can be expected to be more explosive. However, even such future eruptions will only generate waves of short period and their heights will decay rapidly,

 

Morphology of Kick'em Jenny volcano and of an extensive slope failure of unknown age. (NOAA multibeam submarine survey)

 

Tsunami Generation from Submarine Crater Collapses: Even if one or all of Kick'em Jenny's three small craters collapse, no major waves will be generated. For example, when the summit of the submarine volcano Loihi collapsed in Hawaii during the summer of 1996, the wave that was generated was of short period and decayed very rapidly (Mader 2004). The cavity generated by the Loihi collapse was 1000 meters wide and 300 meters deep, which is much greater than any potential cavity that could be expected from collapses of any or all of Kick'em Jenny's craters. The fact that the top of the Loihi cavity was at 1050 meters depth while the top of Kick'em- Jenny's main crater is at 160 meters will not be much of a factor in tsunami wave generation, since the waves will be of short periods and will behave as shallow waves.

Tsunami Generation from Submarine Volcanic Dome Collapses: Similarly, submarine dome collapses on Kick'em- Jenny will probably trigger major eruptions ­ perhaps lateral blasts - with the associated pyroclastic flows and debris avalanches. However, it is expected that the volume of the ejecta and gases will be relatively small and that any resulting tsunami-like waves that will be generated will not be greater than those generated by the 1939 or 1974 eruptions.

Tsunami Generation from Future Subaerial Volcanic c Collapses, Flank Failures and Massive Volcanic Edifice Failures: When Kick'em Jenny breaks through the sea surface and begins to build in height, it is expected that its eruptions will be more violent and that its flanks will be even more unstable than they are now. As with other active Caribbean volcanoes, waves may be generated by violent eruptive episodes, from caldera and dome collapses, from pyroclastic flows, landslides, flank failures, debris avalanches or even massive volcanic edifice failures. However the tsunami waves will be of relatively short periods (1-4 minutes at the most). Although the waves may be significant locally, they will decay rapidly away from the source area.

Worse Possible Scenario: Based on the pattern of Kick'em Jenny's eruptive activity, a "worst case scenario" at the present time would be a repeat of the 1939 eruption but at the shallower depth of the present summit. The waves from the 1939 event were about 2 meters in northern Grenada and the southern Grenadines but substantially lower on the west coast of the Barbados. A large violent eruption similar to the 1939 event, at the present depth of summit, can be expected to generate waves with a probable maximum runup of about 3 meters in Northern Crenada and the Grenadines, and as much as 1-2 meters along the west coast of the Barbados, Trinidad, and St. Vincent. The wave heights along the nearest coastline of northern Bonaire and Venezuela may be up to 1 meter at the most. When the volcano breaks through the surface of the sea, the probable maximum runup could be as much as 4 meters on Northern Grenada and as much as 2 meters along the west coast of the Barbados, Trinidad, and St. Vincent.

CITED REFERENCES AND OTHER PERTINENT BIBLIOGRAPHY

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