The Windward Islands extend south from 15° 45' to 11° 45' North latitude and from 60° 45' to 62° 00' West longitude. (Rand McNally, 1988) They are west of Barbados and northwest of Trinidad and Tobago. From south to north, the islands are: Grenada, the Grenadines, St. Vincent, St. Lucia, Martinique, and Dominica. Martinique is an overseas department of France. The other islands are independent countries. The Grenadines are a string of small islands extending north from Grenada to St. Vincent and include Carricou, Union Island, Mustique, and Bequia. Except for Carricou, which is part of Grenada, the Grenadines are part of St. Vincent and the Grenadines.

The Windward Islands lie within the trade wind belt. The rainy season occurs in summer and fall. Hurricanes and tropical storms pass over the islands during this period. However, the interior highlands of the larger islands also receive rainfall in the drier winter months and additional amounts in the summer months due to orographic uplift (Walsh, 1985). Annual rainfall in the interior highlands ranges from 10,000 millimeters in Dominica to 3750 millimeters for the lower elevation mountains in Grenada. Coastal areas receive lesser amounts ranging from 1000 millimeters on Dominica to 1600 millimeters at the southern end of St. Vincent.

Physiography and Geology of the Windward islands.

Grenada is the least mountainous of the Windward Islands. Its more rugged terrain is concentrated in the central part of the island. St. Catharine at 840 meters is the highest point on Grenada (Rand McNally, 1988). Grenada and St. Vincent are nearly the same size at 344 and 345 square kilometers, respectively. In St. Vincent, the steepest terrain is found around Soufriere, and 1234-meter active volcano at the northern end of the island. The remaining steep terrain extends south through the central part of the island. On the 616-square kilometer island of St. Lucia, the central ridge hosts the steepest terrain with the north and south ends being flatter. The highest point on St. Lucia is 950-meter Mt. Gimie. At 1,100 square kilometers, Martinique is the largest of the Windward Islands. Rugged, Steep terrain is found in the northern and central parts of Martinique. Mt. Pelee, at 1,397 meters, is the highest peak as well as an active volcano. A series of high peaks and connecting ridges runs the length of the 752-square kilometer island of Dominica. The highest peak is Morne Diablotin rising to 1, 447 meters in the central part of the island.

The Windward Islands form a volcanic island arc. Lava flows, ash, and pyroclastic deposits ranging from Miocene to Recent in age are the principal bedrock found in these islands. Some limestones are interfingered with the volcanic layers (Faribridge, 1975c). In general, Grenada, the Grenadines, and St. Vincent are composed of basalts and basaltic andesites. Typically, lava flows outcrop on the steeper slopes and ash underlies the gentler slopes (Walsh, 1985). St. Lucia, Martinique, and Dominica are predominantly composed of acid andesite and dacitic rocks. Pyroclasic flow deposits, volcanoclastics, and lava domes, but few ash deposits, are typical for these islands.

Debris flows, debris slides, rockslides, rockfalls, slumps, and complex landslides are among the types of landslides found throughout the Windward Islands (Faugeres, 1966, Prior and HO, 1972, Walsh 1982, DeGraff, 1985, 1987a, 1988) Most landslides involve either flow or translational movement. Landslide mapping on St. Vincent, St. Lucia, and Dominica found the majority of landslides to be debris flows (DeGraff, 1985, 1987a, 1988). Table 4 characterizes the identified landslides on these three islands.

The Good Hope landslide on Dominica is one of the larger identified debris slides (DeGraff, 1987b). It involved translational movement of a soil mass. Slickenslides were observed at some locations on the exposed failure plane. As it moved, the soil mass disintegrated into a disrupted mass with few discernable internal scarps or coherent blocks. Some flowage developed at the lower end of the slide mass.

From observations of exposed soil in the margins of the failure, the soil appeared residual in origin with no buried horizons, stone lines, or other indicators of significant colluvial accumulation. It is bright red and consists mainly of clay to sand-sized particles mixed with gravel-sized fragments. Some fragments could be crushed to sand by hand.

The failure plane coincided with the contact between the soil and underlying bedrock. Bedrock exposed in the failed area is a fractured, andesite. The failure plane, as defined by the surface of the bedrock, is inclined at 70 to 80 percent. The average thickness of soil over bedrock in the failed area is estimated to be 5 meters. The failed area is roughly circular in plain view and encompasses 3, 630 square meters. These figures lead to an estimated volume of 17, 000 cubic meters.