Grenada
Flag
Location
12.12°N, 61.67°W
Area
344.00 sq km
Capital
Saint George’s
Timezone
Eastern Caribbean (UTC-4)
Population
113,570 (2021 est.)
Full Country Name
Grenada
Geography
Grenada and its dependencies lie north-west of Trinidad and Tobago and south of Saint Vincent and the Grenadines. Grenada consists of the island of Grenada itself plus six smaller islands which lie to the north of the main island .The rugged mainland is the most southerly of the volcanic islands within the Lesser Antilles arc and home to spectacular volcanic features including the Grand Etang Crater Lake. Mt. St. Catherine rises to 910 m Grenada’s highest point. Grenada’s topography is dominated by a generally north-south trending mountainous spine that gives way to narrow coastal plains. Several small rivers provide drainage to these volcanic peaks which experience significant rainfall. A tropical climate supplies the island with 3,500 mm of yearly precipitation at the higher elevations and 1,500 mm closer to sea level giving rise to the island’s overall lush appearance. North-easterly trade winds moderate the island’s day time temperatures to an average of 29˚C year round.
Country Facts
Approximately 113,570 persons live on three main islands: Grenada, Carriacou and Petit Martinique with most living on Grenada. People are referred to as Grenadian. English is the official language with Grenadian creole also spoken. Currency used: Eastern Caribbean Dollar (XCD).
Disaster Management
In the event of an earthquake, volcanic eruption or tsunami the National Disaster Management Agency is the official authority in Grenada.
National Disaster Management Agency
Fort Frederick
Richmond Hill
St. George’s
Grenada
Tel: +1 473-440-0838
Email: nadma@spiceisle.com
Website: http://www.gov.gd/departments/nadma.html
Grenada is the most southerly island in the Lesser Antilles arc. Its basement consists of folded Eocene to Miocene volcanic-sedimentary units which are overlain by an approximately 900 m thick sequence of Miocene to Holocene volcanic rocks (Arculus 1976). The oldest rocks belong to the Tufton Hall Formation comprising well-bedded sequences of calcareous shales, siltstones and sandstones that contain foraminiferal fauna dated as Upper Eocene to Lower Oligocene in age (Martin-Kaye 1961). This formation also contains tuffaceous horizons and thin limestone layers, generally surrounding the northern dome centres. The presence of allochthonous volcanic minerals and tuffaceous horizons indicate that igneous activity was already taking place in the Eocene and probably continued into the Oligocene (Arculus 1973). The Miocene to recent volcanic rocks have been divided into a number of volcanic centres which are described below.
Geology Map of Grenada
Northern Domes Centre
The north edge of Grenada encompasses Mt William, Mt Rodney, Mt Alexander, Mt Craven and Levara Hill centres all representing what is left of andesitic domes. This is the oldest volcanic activity (Miocene) on the island. No summit craters remain, but Arculus (1973) suggests that the generally circular distribution of these domes may be attributed to the massive infilling of a pre-existing crater. The rock types exposed in the area range from basalt to dacite and are mostly weathered. The volcanic history of this area appears to be one in which local eruptions of basalt and andesite lavas were initially interspersed with periods of explosive activity that culminated in the intrusion of domes (Arculus 1973).
South East Mountain Volcanic Centre
The South East Mountain was also active during the Miocene (≈10 Ma). The area is composed of andesite domes (Mt Lebanon), lava flows and pyroclastic flow deposits that radiate from the South East Mountain. The lava flows are so closely intermixed and weathered that it is difficult to distinguish between the different compositions on a map. These flows range in composition from basalt to dacite, although there is a predominance of basalt compositions at the surface. The distal ends of the lava flows overlie and appear to pass through reworked volcaniclastic deposits that form a coastal sheet extending around the southern and eastern coasts of Grenada. Evidence of the contact between the lava flows and the reworked deposits is the presence of a red lateritic soil which contrasts with the grey weathered appearance of the reworked volcaniclastic deposits.
Mt. Sinai-Mt Maitland-Mt Moritz Volcanic Centre
Located in the west of South East Mountan, this centre is generally agreed to have become active during the Pliocene. The centre of activity appears to have been located somewhere in the vicinity of Mt. Maitland and Mt. Sinai. Two main areas are created by the St. John’s River, which flows from NE to SW and separates Mt. Maitland from Mt. Moritz. The path of the St. John’s River may be fault controlled, and the steep northern faces of Mt. Maitland and Mt. Sinai may represent eroded fault scarps. Mt. Sinai is the highest of these centres (~ 703 m), and elevation decreases westwards. The sequence of activity appears to have involved emission of a series of mainly basaltic lava flows and pyroclastic deposits during the Upper Pliocene to Lower Pleistocene. Andesitic and dacitic material is found only as fragments in reworked volcanics interlayered with some of the lava flows.
Mt Granby-Fedon’s Camp Volcanic Centre
This forms the high ground in the middle of the island and is probably a composite centre whose eruptive vents are no longer recognisable. Radiometric dating and morphological evidence indicate that this area was affected by volcanic activity in the Pliocene to Pleistocene (Briden et al. 1979). Lava flows radiate from Mt. Granby (720 m), Fedon’s Camp (820 m) and Mt. Qua Qua (760 m) and may be all part of a single composite volcanic centre (Arculus 1973). The dominant direction of lava flows is westwards. At sea cliffs and in deep river valleys exposures show a repeated alternation of basalt and andesite deposits suggesting a cyclical pattern of transition from silica under-saturated to over-saturated compositions. Generally the source of lava flows appears to shift southwards suggesting a migration of volcanism in this direction (Arculus 1973).
Mt. St. Catherine Centre
Located just south of Northern Domes Centre, this is the youngest polygenetic volcanic centre on Grenada and the only one considered to be live. Although no age dates have been obtained for this centre, it is considered to be of Pleistocene to Holocene age (Arculus 1973). The summit rises to 910 m (the highest point on the island) and is formed of deeply weathered massive andesitic lava. It consists of a 1.7 km wide, horseshoe shaped crater that is breached to the southeast. Within the crater lies a central andesite dome (213 m wide and 122 m high) surrounded by lava flows and pyroclastic flows that are mantled with scree deposits. Several domes (andesite to dacite) have grown in the summit area and some appear to be younger than the collapse of the summit crater (Geotermica Italiana 1991).
Explosion Craters
The most recent activity on the island consisted of the formation of several small craters. They are morphologically well preserved centres of basanitoid, basaltic and andesitic scoria fall and flows, which were formed during the most recent period of volcanic activity on the island. The craters have a maar to tuff ring type morphology, generally 0.5 km in diameter, their size likely depending on the amount of groundwater present during eruptions. Most are composed of silica-undersaturated alkali basalt scoria and ash along with a variety of basement and wall rock fragments. There are no lava flows associated with these craters. Devine (1995) noted that the most recent eruption produced a scoria cone near Radix valley that may be less than 1000 years old. Grenada is characterised tectonically by two conjugate fault trends ((Martin-Kaye 1969, Arculus 1976). The main one runs NNE-SSW and corresponds to the elongation of the island; the other is approximately normal to the main trend. Martin-Kaye (1969) and Arculus (1976) have suggested that the orientation of the explosion craters may be controlled by the main NNE-SSW fault trend
Seismicity in the segment of the Lesser Antilles island arc between Grenada and St. Vincent is markedly lower than along the arc to the north and to the south. Grenada is located within an area of the region that has a moderate seismic risk. There have been few earthquake swarms related to volcanic activity on the island and most felt events have been a result of activity at the submarine volcano, Kick-‘em-Jenny.
Seismicity in the segment of the Lesser Antilles island arc between Grenada and St. Vincent is markedly lower than along the arc to the north and to the south. The epicentral plots reveal that east of the arc shallow and intermediate depth events occur, with the biggest events in this area, for the instrumental period up to November 2017, in the magnitude range 5.1 – 5.5. However, on 2017/11/05, there was an even larger event, at magnitude 5.7, recorded. This may be observed in the plot showing the magnitude distribution of earthquakes in the area since 2000.
Along the arc, there exists a seismicity gap, which may be indicative of aseismic movement or a locked segment. If the latter is the reality, then there may be potential for a major earthquake in the Grenada-St. Vincent vicinity. Evidence for this may be found in the historical records, where there are accounts of felt earthquakes on 1822/12/01, and 1822/12/20 that caused significant damage in Grenada. Maximum associated intensities were MMI VIII and VII respectively. Then on 1834/11/25 there was an earthquake in the area causing a considerable amount of minor damage in St. Vincent. The maximum intensity associated was MMI VIII. Similar earthquakes, or larger, today would cause considerable damage in the area and possibly extending to other nearby islands.
In addition to the earthquakes that arise from tectonic processes, there may also be volcanic earthquakes associated with the submarine volcano Kick-‘em-Jenny and Mt. St. Catherine volcano. Shallow earthquakes were associated with the 2001, 2015 and 2017 Kick-‘em-Jenny eruptions. Some of those events were felt in Sauteurs, northern Grenada. The dense alignment of earthquakes, seen north of Grenada in the epicentral plot, is related to those eruptions. It is anticipated that shallow volcanic seismicity would be associated with the volcanic centres, precursory to any future volcanic activity.
Located in the northern region of Grenada is the island’s only ‘live’ volcano, Mt. St. Catherine. This volcano has not erupted in historic time, but has the potential to erupt in the future. Grenada’s other volcanoes such as Mt. Rodney and Mt. Maitland are considered ‘dead’ and are unlikely to erupt again.
Numerous explosion craters such as Lake Antoine and Grand Etang, represent the most recent volcanic activity on Grenada. These are volcanic craters formed by explosion when rising magma reacts with groundwater or lake water. Most of them are filled with water forming lakes but others such as St. George’s and Queen’s Park craters are dry and populated. They are often referred to as monogenetic volcanoes since they were formed in a single episode of volcanic activity. These are not expected to erupt again, however, new craters can develop in the future. It is not possible to say exactly where these new explosion craters will form.
Kick-‘em-Jenny is a submarine (underwater) volcano about 9 km north of Grenada. It is the only submarine volcano in the Eastern Caribbean known to have erupted in the past 500 years with the most recent eruption being recorded in April 2017. Currently, Kick-‘em-Jenny is most dangerous for ships and boats since the gases released by the volcano can lower the density of the water in its vicinity causing them to sink even if it is not erupting. It is believed that Kick-‘em-Jenny was once a small island before it collapsed into the sea. Learn more about Kick-’em-Jenny here.
Future Eruptions
Mt. St. Catherine is a ‘live’ volcano and will erupt in the future and Kick-’em-Jenny is the most active volcano in the region. An eruption from Mt. St. Catherine may result in pyroclastic flows and surges, lahars and ash fall which will likely affect villages located to the east and west of the volcano such as Grenville and Gouyave. Explosive eruptions would impact a much wider area but are considered to be less likely to occur in the near future. Future volcanic activity in Grenada is most likely to involve phreatic (steam) outbursts from fumaroles (steam vents) associated with Mt. St. Catherine volcano. However, plans should be made for the possibility of monogentic craters developing anywhere along a northeast-southwest trending zone that extends the length of the country. The UWI-SRC scientists provide advice as well as produce maps and other public information material so as to enable the public and authorities to better prepare for volcanic eruptions. Know where Mt. St. Catherine and Kick-‘em-Jenny are in relation to where you live and know what to do if an eruption occurs.
Related Resources
Potentially active volcanic centres
Mt St. Catherine volcanic centre
- 12.16°N, 61.67°W
- Elevation – 910m
- Last eruption – no records
Mount St. Catherine is the only volcanic centre that is considered to be ‘live’ (likely to erupt again) in Grenada.
Past eruptive activity
No eruptions from Mt. St. Catherine have been recorded in historic time. The only evidence of volcanic activity is the presence of numerous hot springs and periodic earthquake swarms. Based largely on field evidence Arculus (1973) proposed that the first eruptions from Mt. St. Catherine probably occurred from a region near to Plaisance and Malagon. Exposures of these early basalt flows can be found at Riviere Sallee and Mt. Ellington. The lava flows were probably widespread but were overlain by more acidic lavas ranging from andesite to dacite in composition. As the volcanic edifice built-up basalts were again erupted along with some pyroxene-phyric lavas. These latter formed the Crayfish area along with the flows found around Peggy’s Whim.
The eruptive centre migrated southwards possibly to the present location of Mt. St. Catherine. A thick sequence of andesitic and dacitic lava flows and pyroclastic flows were produced towards the northwest forming the St. Marks Mountain and the local bedrock found in the rivers. Pyroclastic flows towards the west reached to Gouyave and form the western ridge at Mt. St. Catherine. They represent the best preserved and most voluminous of these types of deposits on Grenada. At the same time andesitic and dacitic lava flows were extruded toward the east forming the eastern ridges found above St. James and Paraclete.
Activity climaxed with the partial infilling of the crater by an andesitic dome. Subsequent erosion and weathering has so altered the materials that it is difficult to correlate the pyroclastic flow deposits with those of the lava flows.
Historical eruptions
There are no historical records of eruptions on Grenada. Anderson & Flett (1903) dismissed reports of an eruption of sulphurous vapours within the harbour of St. George’s in 1867 and 1902. They suggested that these were over-dramatised reports associated with tidal waves generated by eruptions elsewhere in the Lesser Antilles.
Future Eruptions & Conclusion
Based on the geologic record, future eruptions in Grenada may involve activity at Mt. St. Catherine as well as a number of as yet defined monogenetic volcanic centres. Single explosive eruptions from monogenetic volcanic centres similar to those found at Grand Etang and Lake Antoine are possible. There appears to be a poorly defined linear trend to the location of these centres and it is most likely that activity of this type in the future will follow this trend. Specific hazard maps for these types of eruptions cannot be drafted before the actual onset of eruptive activity since the location of such centres cannot be predicted.
In terms of magmatic eruptions, the most likely event will be an effusive dome-building eruption from Mt. St. Catherine the only live volcano on the island. This eruption is likely to develop in a very similar manner to the 1995 eruption of the Soufriere Hills volcano on Montserrat. The potential impact of hazardous volcanic activity on the island may necessitate evacuation of vulnerable communities on the eastern flank of the volcano and provision for further evacuation should the eruption continue.
Three scenarios have been defined for Mt. St. Catherine. It is possible that these may occur as single independent events or they may be simply different stages in the evolution of a volcanic crisis. Scenarios are described in detail in the Volcanic Hazard Atlas of the Lesser Antilles Grenada chapter.
The integrated volcanic hazard maps developed by the SRC should be used by emergency management officials to draft contingency plans for the various scenarios that have been described. One of the key elements in future preparedness must be continuation of the volcano monitoring programme. This will allow authorities to be forewarned of an impending crisis and provide them with sufficient time to fine-time plans which should now be drafted.
Hot springs associated with Mt. St. Catherine are present at Hapsack Hall, Tufton Hall (St. Mark’s), Mt. Ellington, Peggy’s Whim, River Sallee, and Lavez Chaud. Most are sulphurous and they emit hot water at temperatures 50° C. Since the first records were made of these hot springs the temperatures appear to have decreased (Table 2). Most of the springs issue from massively jointed igneous rock. At River Sallee the bedrock is obscured by sulphurous material while at Peggy’s Whim the basement rock is indurated mudflow deposits. In 1985 a field visit to Mt. St. Catherine confirmed areas of geothermal activity in the upper tributaries of the St. Mark’s River in the Tufton Hall Estate ([Shepherd, 1985 #34]). This site is located on the northeastern side of the Mt. St. Catherine volcano and is characterized by ground alterations that were more extensive in the northern tributary. Here the rocks were transformed into yellowish-white material by the actions of hot geothermal water and sulphurous gases. A visit to the area in April 2002 revealed that the region is still hydrothermally active with small fumarolic vents with yellow-brown sulphur deposits (Robertson 2002). Temperatures of the ground in the area ranged from 35.7°C – 41.0°C at the time.
Prefeasibility studies conducted in Grenada noted the presence of several thermal springs in ravines radial to the central volcano, young phreatic explosion craters and one small solfatara on Mt. St. Catherine (Date, 2015). The subsea volcano Kick-em-Jenny lies only 5 miles of Grenada’s north coast which suggests that the zone between it and central northeastern Grenada may be geothermally prospective. In 2015, a comprehensive geothermal survey was completed by Jacobs New Zealand. The results of the surveys provided good indications that the thermal activity in Grenada is of a mature high-temperature geothermal system centered in the area of Mt. St. Catherine with temperatures ≥240°C. The results of the magnetotelluric study conducted in Grenada indicated resistivity patterns typical of a high-temperature geothermal reservoir covering a small area of 4 km2 and a larger area of 8 km2. Urzua et al (2015) recommended that exploration drilling be pursued. However to refine the proposed boundaries of the field and composition of the reservoir, he recommended further infill magnetotelluric (MT) survey of up to 50 stations and a detailed field exploration programme in the area of Belair Estate along with a gravity survey of at least 200 stations to identify the interface of the Mount Saint Catherine volcanic sequences and the Tufton Hall formation.
Arculus, R J. 1973. “The Alkali Basalt, Andesite Association of Grenada, Lesser Antilles.”PhD, University of Durham.
Arculus, R J. 1976. “Geology and geochemistry of the alkali basalt—andesite association of Grenada, Lesser Antilles island arc.” Geol Soc Am Bull 87 (4):612-624.
———. “Mineralogy and Petrology of Grenada, Lesser Antilles Island Arc.” Contributions to Mineralogy and Petrology 65 (1978): 413-24.
Arculus, R.J., and E.B. Curran. “The Genesis of the Calc-Alkaline Rock Suite.” Earth and Planetary Science Letters 15 (1972): 255-62.
Arculus, R.J., and N. Shimizu. Rare Earth Elements in a Suite of Basanitoids and Alkali Olivine Basalts from Grenada, Lesser Antilles. Vol. 73: Carnegie Institute Washington Year Book, 1974.
Briden, J. C., D. C. Rex, A. M. Faller, and J. F. Tomblin. 1979. “K-Ar Geochronology and Palaeomagnetism of Volcanic Rocks in the Lesser Antilles Island Arc.” Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 291 (1383):485-528. doi: 10.2307/75166.
Brown, G.M., J.G. Holland, H. Sigurdsson, J.F. Tomblin, and R.J. Arculus. “Geochemistry of the Lesser Antilles Volcanic Island Arc.” Geochimica et Cosmochimica Acta 41 (1977): 785-801.
Cawthorn, R.G., E.B. Curran, and R.J. Arculus. “A Petrogenetic Model for the Origin of the Calc-Alkaline Suite of Grenada, Lesser Antilles.” Journal of Petrology 14, no. 2 (1973): 327-38.
Date, A.W.2015. The Eastern Caribbean Energy Interconnection Grid Feasibility study, Proceedings World Geothermal Congress 2015, Melbourne Australia
Devine, J 1995. “Petrogenesis of the basalt-andesite-dacite association of Grenada, Lesser Antilles island arc, revisited.” Journal of Volcanology and Geothermal Research 69:1-33.
Earle, K.W. Geological Survey of Grenada and the (Grenada) Grenadines. St. George, Grenada: Government Printing Office, 1924.
Geothermic Italiana, S.r.l. “Reconnaissance Study of the Geothermal Resources of the Republic of Grenada – Final Report.” 126: Latin American Energy Organization, 1981.
GRC Bulletins (https://geothermal.org/about.html)
Graham, A.M. “Genesis of the Igneous Rock Suites of Grenada.” PhD, Edinburgh University, 1980.
Harrison, J.B. The Rocks and Soils of Grenada and Carriacou. London: Waterlow & Sons, 1896.
Hawkesworth, C.J., R.K. O’Nions, and J. Arculus. “Nd and Sr Isotope Geochemistry of Island Arc Volcanics, Grenada, Lesser Antilles.” Earth and Planetary Science Letters 45 (1979): 237-48.
Huttrer. G.W. 2000. Geothermal Activity Status in the Volcanic Caribbean Islands, Proceedings World Geothermal Congress 2000, Kyushu- Tohoku, Japan.
Huttrer. G.W, La Fleur. J, 2015. The Eastern Caribbean Energy Interconnection Grid Feasibility study, Proceedings World Geothermal Congress 2015, Melbourne Australia
Martin-Kaye, P.H.A. “Progress Report No. 12.” Windward Islands: Geological Survey, 1961b.
———. “A Summary of the Geology of the Lesser Antilles.” Overseas Geology & Mineral Resources 10, no. 2 (1969): 172-206.
Ollier, C.D. “Maars. Their Characteristics, Varieties and Definition.” Bulletin of Volcanology 31 (1967): 45-73.
Robson, G.R., and J.F. Tomblin. Catalogue of the Active Volcanoes of the World Including Solfatara Fields. Part 20: West Indies. Rome: International Association of Volcanology, 1966.
Robertson R. and David J. (2002): Ground deformation network on Grenada Sapper, K. “Ein Besuch Der Insel Grenada.” Zentbl. Mineral. Geol. Paleont. (1903): 182-86.
Shepherd, J. B. “Internal Report on the Geological Activities in the Mt. St. Catherine Area. Unpublished Report: Seismic Research Unit, St. Augustine. Trinidad.” 1985.
Sigurdsson, H., J.F. Tomblin, G.M. Brown, J.G. Holland, and R.J. Arculus. “Strongly Undersaturated Magmas in the Lesser Antilles Island Arc.” Earth and Planetary Science Letters 18 (1973): 285-95.
Thirlwall, M. F., and A. M. Graham. “Evolution of High-Ca, High-Sr C-Series Basalts from Grenada, Lesser Antilles – the Effects of Intra-Crustal Contamination.” Journal of the Geological Society of London 141, no. MAY (1984): 427-45.
Urzua. L et al,. 2015. Grenada geothermal surface exploration, Proceedings 37th New Zealand Geothermal Workshop Taupo, New Zealand.
