St. Kitts

Geography

The island of St. Kitts is located in the northern region of the Lesser Antilles. It is 174 square kilometres in size and has a population of 34,983. The main part of the island has a mountain range that runs northwest through the centre of the island. The higher mountain slopes are densely vegetated by rainforest. The foothills gently slope from the base of the mountain range to the coast and are largely covered by sugar cane. Mt. Liamuiga is the most northwesterly mountain and is the highest peak on the island at 1155 m (3792 ft). In contrast, the topography and vegetation of the Southern Peninsula is dramatically different. It consists of numerous low, rounded hills that reach a maximum height of 319 m (1047 ft), but are generally much lower and are separated by flat, low-lying areas and salt ponds. Vegetation is sparse with dryland grasses, low shrubs, cacti and yucca. The sharp contrast in both the topography and the vegetation from the north of the island is in part due to the older age of the rocks and the lower annual rainfall in the south. The capital of St. Kitts is Basseterre, located 12 km southeast of the summit of Mt. Liamuiga.

Country Facts

St. Kitts has a population of approximately 34,983 people with a large number living in the capital city, Basseterre. The population is predominantly of African descent with some British, Portuguese and Lebanese. People are referred to as Kittitian. English is the official language. Currency used: Eastern Caribbean Dollar (XCD).

Disaster Management

In the event of an earthquake, volcanic eruption or tsunami the National Emergency Management Agency is the official authority in St. Kitts.

The National Emergency Management Agency
P.O. Box 186
Lime Kiln
St. Kitts

Tel: +1 869-466-5100
Email: nemaskb@thecable.net
Website: https://nema.kn/

Seismicity Overview

The Leeward Islands area is the most seismically active zone in the Eastern Caribbean and has hosted the largest magnitude earthquakes to have occurred in the region since the 1600’s, when written accounts for the region began. The average number of background earthquakes, i.e. those that recur on a daily/weekly basis, does not change drastically. The output level sometimes increases in association with the occurrence of a significant magnitude earthquake. This can take the form of foreshocks and aftershocks or only aftershocks. Since 2011, activity in the area has been generally elevated over that seen in previous years. Elevated activity is sometimes precursory to more significant magnitude earthquakes.

Volcanism Overview

Mt. Liamuiga is the only ‘live’ or likely to erupt again volcano in St. Kitts. It has had a number of explosive eruptions in the past, but the most recent major eruption occurred 1,600 years ago. It is possible that two small eruptions also occurred in 1692 and 1843. Continuous hot-spring activity and occasional bursts of shallow earthquakes directly beneath Mt. Liamuiga volcano mean that magma (molten rock) is moving beneath the volcano, indicating it is ‘live’ and likely to erupt again.

Future Volcanic Activity

The northern area of St. Kitts near to and around Mt. Liamuiga is the most likely location for future eruptions. The expected style of eruption is an effusive lava dome-forming eruption similar to the current Soufriere Hills eruption in Montserrat. Molten rock (magma) reaches the Earth’s surface and erupts passively or quietly as opposed to an explosive eruption which is more violent. Both types of eruptions can have associated volcanic hazards such as pyroclastic flows and surges, ash fall and lahars. Should there be an eruption, the National Emergency Management Agency is the first point of contact in St. Kitts and areas near the volcano are most likely to be evacuated. 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.

There are four volcanic centres on St. Kitts: the Salt Pond Peninsula, South East Range, the Middle Range, and Mt. Liamuiga (Martin-Kaye 1959).

The Salt Pond Peninsula is dominated by lava domes with minor volcaniclastic deposits that are interpreted to be pyroclastic flow (block and ash flow) deposits and/or lahar deposits. Ages of 2.3 ± 0.6 Ma, 2.3 ± 0.5 Ma and 2.77 ± 0.3 Ma (Baker 1969) were obtained for lava domes of this centre. These are the oldest known ages for volcanic deposits on the island of St. Kitts. The South East Range is a youthful-looking volcano that has a partly preserved crater at its summit (Baker 1969). Ottley’s Level and Monkey Hill are lava domes that formed on the flanks of the volcano.

The South East Range mainly consists of lava flows and volcaniclastic deposits (Baker, 1969) although it is poorly exposed and little is known about its past eruptive history. An approximate age of 1 Ma was obtained from a lava flow on the southern slopes of the South East Range (Baker 1985). The age, lack of seismicity and lack of geothermal activity suggest that both the Salt Pond Peninsula and the South East Range are unlikely to be the sites of future volcanic activity.

Geology map of St Kitts (adapted from Baker, 1969).

The Middle Range also has a youthful appearance and has a small summit lake that has filled a former crater. The Middle Range is poorly exposed and there are few descriptions of its geology, although Baker (1963) described it as consisting of similar deposits to the South East Range. There are no age dates available for the Middle Range. Previous workers have considered the Middle Range to be extinct; however, its youthful appearance, and the lack of age dates makes the current state of the volcano difficult to interpret. New information (i.e. age dates) is necessary to clarify its eruptive history. There is no geothermal activity and no seismicity associated with the Middle Range at present.

Mt. Liamuiga is the youngest of the volcanic centres and probably last erupted about 1620 years BP (Baker 1985). The age, geothermal activity and seismicity associated with Mt. Liamuiga suggest that it is a potentially active volcano and likely to erupt again in the future.

The Leeward Islands area, as shown in the epicentral plot, is the most seismically active zone in the Eastern Caribbean and has hosted the largest magnitude earthquakes to have occurred in the region since the 1600’s, when written accounts for the region began. The average number of background earthquakes, i.e. those that recur on a daily/weekly basis, manifest minor fluctuations. The output level sometimes increases in association with the occurrence of a significant magnitude earthquake. This can take the form of foreshocks and aftershocks or only aftershocks.

One such period in 2000-2001 exhibited elevated earthquake activity associated with a magnitude 5.6 event on 2000/10/30 that was located east of Barbuda. However, since 2011, activity in the area has been generally elevated over that seen in previous years. Elevated activity is sometimes precursory to more significant magnitude earthquakes. In the epicentral plot shown for the period since 2011, the moderate to strong earthquakes are labelled. Whether or not the elevation being observed is associated with those events or indicative of a more significant magnitude event to come, only time will tell. It may be worthy of note that on 2011/09/06, there was an earthquake of magnitude 5.6 located at 21.66°N and 60.20°W, which is an unusual area for earthquakes to occur and significantly extends the area of increased activity.

During the instrumental era, since 1953, there have been a number of strong to major earthquakes in the area. On 1974/10/08, there was a magnitude 7.4 earthquake located north-east of Antigua/south-west of Barbuda causing damage at Modified Mercalli Intensity VIII in Antigua and lower intensities in the more distant islands. The damage was confined mainly to larger and older buildings, to a petroleum refinery, and to a deep-water harbour. A few people received minor injuries, but no fatality was reported. Then on 1985/03/16, there was a magnitude 6.3 event located west of Antigua/south-east of Nevis that was strongly felt in Montserrat, Nevis, Antigua and St. Kitts.

During the historical era, which dates back to the 16th Century, the first major earthquake in the area, for which there are written accounts, is estimated to have been located close to Nevis and occurred on 1690/04/05. The damage accounts in Robson (1964) suggest impact at Modified Mercalli Intensity IX: In Antigua, some buildings collapsed into rubble, with some associated deaths. Governor Codrington, the then Governor, lost property with value estimated at £2,000. Aftershocks were felt almost daily for a month.

The region’s great earthquake, at magnitude estimated to be in the range 8.0-8.5, was also located in this area, south-east of Antigua, on 1843/02/08. In this instance also, the maximum intensity, based on damage accounts, has been put at Modified Mercalli Intensity IX. In St. Johns, Antigua and across the island generally all masonry structures were destroyed or severely damaged. Many houses were left with their outer masonry walls collapsed and the inner walls supporting the roof. Wooden houses remained standing. Alluvial ground was fissured and sulphurous water thrown out. Landslides were general on hill slopes. At English Harbour the wharf, built on reclaimed ground, sank and afterwards had an undulating appearance ‘like waves on the sea’. A cloud of dust hung over the island for some minutes after the earthquake. After the earthquake the sea rose four feet, but sank again immediately, remaining calm throughout. The number killed was variously estimated in the range 12-40. The damage at English Harbour was variously estimated at £20,000-£25,000. The total damage in Antigua including the loss of the sugar crop was estimated at £2,000,000.

The occurrence of such events in the past should be taken as clear evidence of the potential for high level damage from large magnitude earthquakes in the Eastern Caribbean. The absence of such events in the 20th Century should serve to motivate to urgently putting measures in place to mitigate the impact of such events that would in all likelihood occur this Century.

Mt. Liamuiga

• 17.37°N, 62.81°W
• Elevation – 1155m
• Last eruption – 1843 (unsubstantiated report)

Mt. Liamuiga rises to a height of 1155 m (3792 ft) and has a summit crater ~900 m wide and 244 m deep. The summit of Mt. Liamuiga exposes remnant lava flows and/or domes but the most common deposits identified on the lower flanks of Mt. Liamuiga are pyroclastic deposits. Cliff exposures along the coastline reveal 5-30 m thick successions of pyroclastic deposits (fall, flow and surge deposits), debris avalanche deposits and lahar deposits. Lava domes are prominent on the flanks of the volcano at Brimstone Hill, Sandy Point Hill and Farm Flat. There are also apparently two small craters located on Bourke’s Estate (Baker, 1965) although these could not be located during this study and their origin is unknown. Age dates on deposits interpreted to have been erupted from Mt. Liamuiga range from 1620 to > 41,000 yrs BP . These are the youngest known deposits on the island. The lava domes on the flanks of the volcano have not yet been dated and it is not known what the relative ages of these features are with respect to the dated pyroclastic deposits from Mt. Liamuiga.

Mt. Liamuiga principally formed by effusive lava-dome forming eruptions. Periodically the lava dome collapsed producing pyroclastic flows, surges and airfall. During and after periods of heavy rainfall it is likely that lahars or mudflows were also common. A final phase of explosive magmatic activity is interpreted to have formed the steep-walled, deep crater that is present at the summit of Mt. Liamuiga and to have produced the thick succession of airfall deposits that blanket the NW part of the island.

Fumaroles are present within the crater of Mt. Liamuiga as well asand on the flanks of the volcano along the SW base of Brimstone Hill and along the coast below Brimstone Hill. Volcanic earthquakes have also been associated with Mt. Liamuiga.

Historic Eruptions

There are two unsubstantiated reports of historic eruptions of Mt. Liamuiga in 1692 and 1843. The first report was by a Franciscan friar (Sloane 1694) who describes the island as being troubled by earthquakes and mentions an eruption “of a Great Mountain of Combustable Matter”. The second report comes from Capadose (1845) who describes a white spiral cloud of smoke and bubbling sulphurous springs from the crater of Mt. Liamuiga. There are no other historical reports to support the occurrence of either eruption and both of these alleged eruptions occurred immediately after major earthquakes. It is possible that the effects of the earthquakes were confused with genuine eruptions or that the earthquakes could have triggered minor eruptions.

Baker (1985) references S. Skerrit (pers. comm.) as describing a Carib legend about Brimstone Hill suggesting that the hill grew out of the lower slopes of Mt. Liamuiga. This suggests that the pre-Columbian Indians possibly witnessed the growth of Brimstone Hill.

Future Eruptions

Present and past studies indicate that the northern part of St. Kitts near to Mt. Liamuiga is the most likely location for future eruptions. The most likely style of eruption is an effusive lava dome-forming eruption. There is also evidence of past occurrences of explosive magmatic eruptions resulting in pyroclastic , fall deposits; however, in the past dome growth and collapse have been the dominant processes. Future effusive eruptions may occur either on the flanks of Mt. Liamuiga (e.g. as at Brimstone Hill) or within the crater itself.

Related Resources

Volcanic Hazard Atlas of the Lesser Antilles

Active low temperature (up to 100oC) fumaroles are present in the crater of Mt. Liamuiga. Cracks within the limestone at the base of Brimstone Hill emit a strong smell of sulphur but no steaming was observed by Simpson and Shepherd (2002). The temperatures within these cracks were only slightly elevated and sulphur crystals line the cracks locally. A strong smell of sulphur is also present along the coastline below Brimstone Hill. No obvious source for the smell was observed; however, discoloration of rocks near the shore may indicate that the vents are located just offshore and that diffuse venting occurs through the ground along the coastline.

Brimstone Hill National Park. Strong sulphur smells and discolored rocks in the vicinity of this andesite dome suggests that there may be fumarolic vents located at the base of the dome and along the coastline to the west (left of the photograph).

Crater of Mount Mt. Liamuiga showing one of several areas of fumarolic activitiy located along the crater walls. The photograph shows the fumarolic field on the northern crater walls and is taken from the top of the track leading to the crater rim.

St. Kitts and Nevis are volcanic islands that have the potential to harness geothermal energy. Both islands have been engaging in geothermal exploration studies. In 2008, West Indies Power Company drilled three small diameter exploratory wells about 3.7 km apart to depths ranging 782 to 1134 meters in the Spring Hill, Jessups and Hamilton estates areas in Nevis. All encountered temperatures greater than 250 °C. In September 2017, new geothermal exploration techniques conducted in the northwest of St.Kitts (Teranov Geothermal Energy, 2017) estimated the temperature of the reservoir as 212 °C. This data along with structural and geophysical work completed help to conceptual model the geothermal resource and estimate the potential of the resource between 18 to 36 MWe. Power plant construction is estimated to begin in 2019.

Since 1957, Mt Liamuiga has been monitored continuously by a single short-period seismograph1 station at Bayfords Farm, 8 km southeast of the crater. Geothermal activity is also being monitored for changes in location, chemistry, temperature and vigour. Ground deformation is monitored using a GPS2 network of 7 stations, 4 at the periphery, 2 on the flanks and one on the summit of Mt. Liamuiga.

Monitoring Network, St. Kitts.

Glossary

1 Seismograph. A group of instruments used to record earthquakes. A seismograph includes a seismometer as well as all equipment used to convert, transmit and display the signals generated by the seismometer.

2 GPS. GPS stands for Global Positioning System. This is a geophysical technique used to accurately determine the locations of specific points in three dimensions. Very small (mm scale) changes in the locations of these points can be recorded over time.