Fascinating Caves and Other Geological Features of Barbados, West Indies Arun Kumar

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Fascinating caves and other geological features of Barbados, West Indies Arun Kumar

geology of Barbados explains presence of several caves in this island. Harrison’s Cave is the most fascinating and beautiful. Continuous rainfall and ground water movement are constantly eroding the surface and subsurface coral bed formations creating wonderful caves.

It was January 2013, when Ivisited Trinidad and Tobago again on the invitation of my Trinidadian family friends Ramesh and Dolly Ramcharan. Last time I visited Trinidad in November, 1975, when I was a graduate student working for my Ph.D. degree at Michigan State University, U.S.A. It was a very good escape from the severe Canadian winters we face in our beautiful Ottawa. Out of my professional interest as a geologist, I visited La Brea Pitch Lake and other places of geological interest in Trinidad and I had published a popular geological article about them (Kumar, 2012). This article is in continuation of the earlier one providing more geological details about Barbados.

Barbados is an actively rising island in the North Atlantic Ocean; located at Latitude 13 10 N and Longitude 59 32 W it is the easternmost isle of the Lesser Antilles; 100 km east of the Windward Islands in the Caribbean Sea (Figure1; Website1). Its total land area is 430 km2 and has a 97 km long coastline. Barbados has a north-south length of 34 km and east-west breadth of 23 km. The physical characteristics of this island are gently sloping lowlands and rolling hills. The 340 m high Mount Hillaby is the highest point in the island but the average elevations range between 180 and 240 m above the sea level (Figures 2, 3). Most of the island's surface consists of 24 to 30 m thick coralline limestone. But in the northeast of the island in the Scotland District outcrops of oceanic sediments occur at the surface where small streams are present. Rainwater saturates the soil to produce underground channels such as the famous Coles cave. The north and East Coasts face the Atlantic Ocean; these coasts are really dangerous with very high waves and strong currents. The west coast of this island faces the Caribbean Sea and has beautiful beaches that are extremely popular with tourists.

Barbados is not a part of the Arc of Caribbean islands. This island is largely surrounded by coral reefs resulting in the fine, white sand that makes the beaches. Before the arrival of Europeans here, there were numerous mangrove swamps surrounding the island but many were later destroyed due to the construction of hotels. Only few such swamps remain now, e.g. the Chancery Lane Swamp

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

and the popular Graeme Hall Swamp. New efforts are on to preserve the swamps and coral reefs and several ships have been sunk at strategic points along the island to make artificial reefs (Website 3).

Figure 1: Location of Barbados in relation with the Lesser Antilles in the Caribbean Sea (Website 1)

Figure 2: Geography of Barbados showing urban centers (Website 2). 2

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Geology and the Origin of Barbados

Barbados is not a volcanic island like other islands of the Eastern Caribbean and is older than its volcanic neighbours. It is located at the crest of the Barbados Ridge, an accretionary prism of the Lesser Antilles forearc. This accretionary prism also termed the ‘Barbados Ridge’, is a bathymetric feature situated east of the Lesser Antilles ridge magmatic arc (Website 4). Barbados is the only emergent peak of the Barbados Ridge complex.

Barbados originated by the gradual accumulation of the oceanic sediments and regular tectonic uplifts caused by subduction of the Atlantic plate under the Caribbean plate that pushed Barbados upwards to the surface. The exposed part of the Barbados Ridge gradually rose when coral reefs developed around it in clear, shallow and warm waters. Between 500 and 120 kyr before present, Barbados became enlarged by tectonic uplifts that pushed these reefs out of the water forming 'inland reefs' seen as terraces and cliffs around the island (Website 5). Except for the highlands, the deformed Tertiary strata are unconformably overlain by a succession of Pleistocene; tectonically little affected, reef terraces that topographically run down toward the northern, eastern and southern coastlines almost concentrically becoming younger toward the coastline. The Upper Reef Terrace is older than 600 000 years whereas the youngest reef terrace submerged off the Lower Reef Terrace is of the Holocene-Recent age. The terraces formed in response to the tectonic uplift and eustatic sea-level fluctuations resulted in several episodes of relative sea-level drop. Refer to DeMets et al. (1990, 1994); Dengo and Case (1990); Dixon et al (1998); Donovan and Harper (2005) and Draper and Dengo (1990) for details about the origin and geology of Barbados.

Figure 3: A view of rural Barbados (Photo: the author, January, 2013)

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 4: Reception center and museum of Harrison’s Cave, Barbados (Photo: the author, January, 2013)

Figure 5: Stalactites in the Harrison’s Cave (Photo: the author, January, 2013)

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 6: Stalactites in the Harrison’s Cave (Photo: the author, January, 2013)

Pleistocene coral reef limestone covers about 85% of the island and Tertiary marine sediments cover the remaining 15% forming a 40 km2 inlier in the Scotland District in northeastern Barbados. There are four stratigraphic units in Barbados namely, Coral Limestone, Oceanics Formation, Intermediate Unit and the Scotland Formation in descending order (Website -6; Table - 1). The oldest rocks on Barbados are exposed in the Scotland District as pelagic shales, sandstones, and siltstones, ash layers, chalks, and radiolarites. These rocks are folded and faulted mainly due to the Late Tertiary to Quaternary compressional deformation and uplift. The Scotland Formation (late Eocene sandstones and clays) as well as the Oceanic Formation (mid Eocene-Miocene turbidites and deep water biogenics) are two stratigraphic units that outcrop in the Scotland District (Donovan and Harper, 2005).

Reefs occur in the western coast of the island where a gradually sloping shelf extends about 300 m seaward to a depth of 10 m. Fringing reefs grow as narrow segments of semi-circles. Lithothamnion sp. and sparse colonial growths of Porites porites, P. astreoides, Siderastrea siderea and Millepora alcicornis constitute these reefs. Further offshore a slowly growing barrier reef, 12 to 20 m deep and up to 100 m wide, runs parallel to the coast that extends from north to south.

Caves of Barbados

The geology of Barbados explains presence of several caves in this island. Harrison’s Cave is the most fascinating and beautiful. Continuous rainfall and ground water movement are constantly eroding the surface and subsurface coral bed formations creating wonderful caves.

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Table-1: The stratigraphy of Barbados. Series Stage Zone/Formation Pleistocene Pleistocene/Corals Reef, Coral rock Miocene to Late Oceanics Oceanics Eocene Upper Intermediate Shale Intermediate Sands Intermediate Unit Lower Intermediate Sands Upper Scotland Sands Middle & Lower Basals Eocene Upper Scotland Shale Basal Complex, Upper and Lower Scotlands, Joes River Joe's River and Basals Lower Scotland Sands Lower Scotland shale

Figure 7: Stalactites in the Harrison’s Cave (Photo: the author, January, 2013).

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 8: Stalactites in the Harrison’s Cave (Photo: the author, January, 2013)

Figure 9: Stalagmites in the Harrison’s Cave (Photo: the author, January, 2013)

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 10: Stalagmites and a water pool in the Harrison’s Cave (Photo: the author, January, 2013)

Harrison’s Cave

Harrison’s Cave and park (59º 34’ 29” W 13º 10’ 54” N) is located in the central uplands of the island in the parish of St. Thomas, a famous tourist location (Figure 4). It is situated at 214 m above the sea level. Tourists are taken in an electric powered ‘tram’ along an underground roadway that follows the former course of underground streams. These caves were mapped in 1974 by Ole Sorensen, an engineer and cave adventurer from Denmark, who was assisted by Barbadians Tony Mason and Allison Thornhill. The government of Barbados opened these caves to the public in 1981.

These are a series of caves that were developed within the Upper Coral Rock (Poole and Barker, 1983) and are only about 1 km south of the edge of the Scotland District and close to the highest point of the island, Mount Hillaby (340 m; Gordon et al., 1986). The thickness of the crystalized limestone in this area varies between 52 and 66 m. A variety of speleothems like stalactites (Figures5-8; 13-15), stalagmites (Figures 9-11; 13-15) and flowstones (Figures 13, 15) beautify these caves.The caves have flowing streams (Figures 10, 13, 16), falls (Figure 12) and water pools (Figures 14, 15, 17) of various sizes. Harrison’s Cave is an active stream cave system at least 2.3 km long. Its largest cavern called the ‘Great Hall’ (Figure 18) is 15 m high. View the following Youtube videos about these caves and beaches of Barbados.

http://www.youtube.com/watch?v=bDv8NEpjUzw http://www.youtube.com/watch?v=CgHdT5y-Xqo http://www.youtube.com/watch?v=ZKbF683NVdA

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 11: Stalactites, stalagmites and flowstones in the Harrison’s Cave (Photo: the author, January, 2013)

Figure 12: Flowstones and a flowing stream forming a water fall in the Harrison’s Cave (Photo: the author, January, 2013)

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 13: Stalactites and stalagmites and a water stream in the Harrison’s Cave (Photo: the author, January, 2013)

Figure 14: An underground large water pool with very small stalacties and few stalagmites in the Harrison’s Cave (Photo: the author, January, 2013) 10

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 15: An underground water pool with stalacties and stalagmites in the Harrison’s Cave (Photo: the author, January, 2013)

Figure 16:An underground water stream in the Harrison’s Cave (Photo: the author, January, 2013)

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 17: An underground water pool in the Harrison’s Cave (Photo: the author, January, 2013)

Figure 18: Ramesh and Dolly Ramcharan and the author (right) in the ‘Great Hall’ of the Harrison’s Cave (Photo: a fellow tourist, January, 2013)

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Animal Flower Cave

Animal Flower Cave (59º 36’ 50” W 13º 19’51” N) is located under the cliffs at North Point, in St. Lucy parish, close to the northern-most point in Barbados. There is a staircase that descends into the caves (Figure -19, 28). These caves are named ‘animal flowers’ because of invertebrate animals such as sea anemones and a tube-dwelling worm, the seafeather Sabellastarte magnifica (Shaw), that inhabit the water pools of the cave (Ali, 1996). The caves open to the Atlantic Ocean and offer a wonderful view of the ocean and the rugged cliffs of northern Barbados (Figures 20-22). The caves are formed in the Middle Coral Rock having boulders and fractions of various sizes including corals and algal mats (Figures 23-28). The walls of the Cave are full of interesting formations that have been coloured green and brown by the oxidation of copper and iron. View the following Youtube videos about Animal Flower Cave.

http://www.youtube.com/watch?v=TDbRvmhKvmo http://www.youtube.com/watch?v=3H9n42q7UsM

Figure 19: Entrance to the Animal Flower Cave (Photo: the author, January, 2013)

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Figure 20: The caves open to the Atlantic Ocean offer a wonderful view of the Atlantic Ocean (Photo: the author, January, 2013)

Figure 21: The caves open to the Atlantic Ocean offer a wonderful view of the Atlantic Ocean (Photo: the author, January, 2013)

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Figure 22: The caves open to the Atlantic Ocean offer a wonderful view of the Atlantic Ocean (Photo: the author, January, 2013)

Figure 23: Inside the wall of the caves showing various sizes and shapes of rocks, corals and algae. (Photo: the author, January, 2013) 15

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 24: Inside the wall of the caves showing various sizes and shapes of rocks and corals. (Photo: the author, January, 2013)

Figure 25: Inside the wall of the caves showing various sizes and shapes of rocks and corals. (Photo: the author, January, 2013)

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Figure 26: Inside the wall of the caves showing various sizes and shapes of rocks, corals and algae. (Photo: the author, January, 2013)

Figure 27: Inside the wall of the caves showing various sizes and shapes of rocks and corals. (Photo: the author, January, 2013) 17

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VI (II), April, 2013, p. 1-21

Figure 28: Base of the cave showing rounded to subrounded rocks of various sizes indicating constant impact of waves in the caves. The author, Ramesh and Dolly (left) inside the cave. (Photo: our guide, January, 2013)

Mushroom Rock and Limestone Boulders at Bathsheba

On the Atlantic coast of this island there are large numbers of loose limestone boulders (59º 31’ 12” W 13º 12’ 35” N); some of them are of immensely large size and lie in the shallow waters and on the beaches (Figures 29, 30). Donovan and Harper (2005) provide the following details about these fallen limestone boulders,“These limestone boulders, some as big as a house, are presumably derived from the face of the Hackleton’s Cliffs to the south west. A cliff on a rocky coastline presents one face to the sea and will develop a sea level or intertidal notch at its base. The tidal range in the Caribbean is less than one metre, which is reflected by the height of the notches in these fallen boulders. However, unlike a cliff, these boulders present all sides to the sea and have developed a notch through 360º, hence their distinctive shapes like a group of top heavy limestone mushrooms. The notch is typically deep, the well-lithified limestones not collapsing until the ‘stalk’ of the mushroom is slender. The notch is not formed by the erosive action of the sea per se, but rather by the feeding action of herbivorous invertebrates scraping algae from the limestone. Typical eroders would be the radulae of chitons and gastropods, and the Aristotle’s lantern of regular echinoids (Bromley,1975). At low tide it is apparent that the notch is floored by a horizontal platform that is the remnant of the base of the boulder.”

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Figure 29: Mushroom rock and other large limestone boulders on the Atlantic side of Barbados. The author is standing on the beach. (Photo: Dolly Ramcharan, January, 2013).

Figure 30: A very large limestone boulder on the Atlantic side of Barbados. (Photo: the author, January, 2013).

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Geological significance of Barbados

The island of Barbados is the sub-aerially exposed tip of the Barbados Ridge. This ridge comprises of over 4 km thick Tertiary sediments (Donovan and Harper, 2005). The exposed core of the Barbados Ridge consists of deformed turbidites, volcanogenic strata, olistostromic blocks, conglomerates and possible mud volcanoes and deltaic deposits. Barbados is one of the few places in the world where an active accretionary prism is exposed (Speed, 1994, 2002). With the exception of some volcanic ash bands, the rock succession in Barbados is entirely sedimentary in origin, demonstrating its geological independence from the volcanic arc of the Lesser Antilles (Donovan and Harper, 2005). The deformed Tertiary rocks in the Scotland District are considered to show a structural complexity indicating that they are considerably displaced with respect to each other. Speed (1988) suggested a seven phase evolution of Barbados, prior to the deposition of the autochthonous Pleistocene reefs.

Barbados is a very important location for paleoclimate studies; it is a classic field area for Quaternary sea level study as well. It is an actively rising island situated at the crest of the Barbados Ridge; an accretionary prism of the Lesser Antilles forearc. Strongly folded and faulted Eocene marine sediments are capped by a sequence of Quaternary coral terraces formed during the sea level changes that occurred over the last 700,000 years. Most of the presently known information about the rates and magnitudes of Quaternary sea level change comes from studies of the uplifted reef tracts of this island and cores recovered from the drowned deglacial coral reefs offshore. The first strong support for the Milankovitch theory of climate change came from the dating of the Last Interglacial terrace, that was locally know as the First High Cliff. This date was key to establishing a timescale for the oxygen isotope record that remains our primary way of establishing a stratigraphy andtimescale for all ocean cores (Website 7).

Acknowledgements: I am grateful to Ramesh and Dolly Ramcharan for their kind invitation as well as the love and care they showered on me during my stay with them at their home in Tacarigua, Trinidad. They also took me to Barbados and this piece would not have been possible but for this trip. I dedicate this article to the memory of my fiancée late Ramkumarie (Manisha) Ramcharan who suddenly passed away 37 years ago on April 3, 1976 at a very young age. Just one month before her death she along with her cousins and friends had spent a week in Barbados and visited several places that I describe in this article. I thank my son Anshuman Kumar for linguistic improvements in this write-up.