Barbados experiences wet summers and dry winters associated with a tropical humid climate. Annual precipitation varies from 1008 mm on the coasts to 1650 mm in the interior (Peeters, 1963). Barbados lies within the main hurricane track of the Caribbean.
Geology of Barbados
Geologically, Barbados is an interesting island consisting of uplifted deep-sea facies and Pleistocene coral reefs (Fairbridge, 1975a). The higher elevations in the north are generally capped by Pleistocene coral reefs or limestones and marls of possibly Oligocene or Miocene age. These limestones overlie an oceanic series representing a deep marine facies. The oceanic series is exposed on Mt. Hillaby and higher elevations to the southwest. Chalks, marls, volcanic tuff, and mudstone are the main components of the oceanic series. A thick sequence of mudflows of probable Eocene age called the Joes River Formation underlie the oceanic series. The core of the island under the Joes River Formation is the Scotland Beds. These beds outcrop on the eastern part of the island in the Scotland district. It is essentially a flysch facies (Fairbridge, 1975a).
Landslides in Barbados
Earthflows, slumps, and debris flows are the main landslide types present in the Scotland District. These failures occur on the upper, steep slopes within the District and along steep slopes of deep v-shaped valleys and sharp-crested ridges formed by stream dissection (Prior and Ho, 1972, Peeters, 1963). These landslides are commonly shallow failures within a few m to tens of m of the ground surface. Prior and Ho (1972) found shallow debris flows and slides on slopes between 20 and 30 degrees. On the steeper slopes immediately below the escarpment delineating the Scotland District, some large slides have rafted large blocks of the oceanic series and limestones downslope (Peeters, 1963).
Landsliding in the Scotland District is directly related to the response of clay present in the Joes River Formation and Scotland Beds. Kaolinite, illite, chlorite, and montmorillinite clays are present in the soils. The kaolinite is largely inherited from the parent bedrock of the Joes River Formation and Scotland Beds (Prior and Ho, 1972). Montmorillinite content is very variable within these soils. Where this clay is present in significant quantities, the landslides tend to exhibit a greater tendency for flowage. Failures occur when the clay-rich soil experiences a decrease in strength resulting from increased pore-water pressure. Increased pore-water pressure may be in direct response to intense rainfall. In other instances, pore-water pressure builds on perched water tables associated with the bedding within the bedrock or older clay-sealed slip surfaces. Near the escarpment, percolation downward through the limestone permits lateral seepage to produce higher pore-water pressures during heavy rains. This mechanism apparently produced significant slope movement in 1966 after 406 mm of rainfall was received in two days (Prior and Ho, 1972).
Roads within the Scotland District incur damage where undermined by failing slopes and blocked by displaced slide material. Activation in early November 1987 of a small earthflow removed support from a two-lane collector road near Welch Town. The entire road prism along a section roughly 50 m long was displaced 3 to 4 m vertically. This effectively closed the road. Because repairs were not yet underway, the cost of restoring this road section is unknown.
Agriculture is the other primary economic impact. Peeters (1963) notes some land is rendered untillable by landslide activity. Ground cracking, scarps, and gully development are some of the consequences of landslides which renders land unusable for farming. Other locations are threatened by active landslides. Concern is expressed for yet other areas where the circumstances associated with active landslides are present but no landsliding is evident. Soil conservation efforts include efforts to prevent pore-water pressure increases through drainage techniques (Cumberbatch, 1966, Peeters, 1963). The cost of such mitigation efforts are not described in published reports.
The island of Barbados is located northeast of Trinidad and Tobago and due east of the Windward Islands. It is the easternmost island in the Caribbean and is situated at 13° 15' North latitude and 59° 30' West longitude (Rand McNally, 1988). This independent island nation is 430 square kilometers. Mount Hillaby, at 340 meters, is the highest point. There are about 250,000 inhabitants of Barbados.
Small-scale landsliding is associated with coastal escarpments where instability results from undercutting by wave-action. However, the principal landslide activity on Barbados is confined to the Scotland District on the northeast part of the island (Fig. 6.). Price (1958) notes reported soil movement in the Scotland District dating from as early as the mid-eighteenth century. While these reports are very general, they describe soil sliding in large pieces with some violence which suggests landslide movement. These early reports establish landslide activity as a recurring and important geomorphic process in this part of Barbados.
Economic Impacts of Landslides in Barbados
Economic impacts attributable to landslides are limited to the Scotland District. Little detailed information on the cost of landslide damage to infrastructure or agriculture is available. Cumberbatch (1966) refers to recent catastrophic landslides devastating villages and estates but provides no specifics. It is inferred from a reference cited that considerable damage occurred in the Boscobelle area on October 4, 1901.
Fairbridge, R.W., 1975a. Barbados. In R.W. Fairbridge (ed.), The Encyclopedia of World Regional Geology, Part 1: Western Hemisphere, p. 115. Stroudburg, Dowden, Hutchinson and Ross.
Peeters, L., 1963. Erosion et glissements de terrain a La Barbade. Rev. Belge Geographie 87:211-225.
McNally, 1988. World atlas of nations. New York: Rand McNally
Prior, D.B. and C. Ho, 1972. Coastal and mountain slope instability on the islands of St. Lucia and Barbados. Eng. Geol. 6:1-18.
(Taken from: DeGraff, J.V., Bryce, R., Jibson, R.W., Mora, S., and Rogers, C.T. 1989. Landslides: Their extent and significance in the Caribbean. In E.E. Brabb and B.L. Harrod (eds), Landslides: Extent and Economic Significance. p. 51-80. Rotterdam: A.A. Balkema. )
Transcribed by Nicholas DeGraff, University of California at Santa Cruz
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