Location

The Island of Grenada, capital St. George – 12 degrees 03’ N. 61 degrees 45 W., lies geographically within the Caribbean Sea. This is achieved by a convention delimiting the Atlantic Ocean and the Caribbean Sea. From Point San Diego (Puerto Rico) Northward along the meridian thereof (65 degrees 39’W) to the 100 fathom line, thence Eastward and Southward, in such a manner that all islands, shoals and narrow waters of the Lesser Antilles are included in the Caribbean Sea as far as Galera Point through Trinidad to Galeota Point (Southern extreme) and thence to Baja Point (9 degrees 32’N. 61 degrees W) in Venezuela, thereby including Tobago and Barbados as Caribbean islands. The Island is caught between the rough Atlantic Ocean which gnaws away the eastern (windward) coast while the gentle Caribbean Sea laps the western shore.

The Island is the highest remaining portion of the Grenada Bank – a volcanic entity, with sheer submarine cliffs, stretching from the island of Bequia in the North to Reindeer Shoal in the South. Such deep water separates this shelf and from the volcanic island of St. Vincent, from the Barbados shelf and from the geologically recent “continental islands of Trinidad and Tobago, that no land-bridge can be postulated as biological contacts.

Grenada (approximately: 21 X 12 miles) and the Grenadine Islands are in fact the remnants of an “Oceanic Island” which appeared in the late Miocene as a contemporary of parts of the Andes Mountains. Considering that the tropical sea-level was at least 50 fathoms lower in the Glacial Epoch of the northern hemisphere and allowing for subsequent erosion of soft volcanic ash, the Grenada Bank would have been almost wholly above water at this time. Plants and animals reaching any part of this shelf, by air or water, would no doubt have spread throughout its length and finally have become isolated in the hilly regions as the actual and apparent level of the water rose.

Geological History

Grenada’s Geological History began 38 million years ago in the Upper Ecocene Period. At that time, there was only a shallow sea where Grenada now exists. The sediments deposited were composed of sand, silt, mud and calcareous mud; the rock formed from this deposition is now known as the Tufton Hall formation. Volcanic activity became more frequent in the Oligocene Period (37 to 26 million years ago). The volcanic activity during and following the deposition of the Tufton Hall Formation deformed and uplifted the rock, resulting in the folding and faulting which can be seen just north of Levera Beach.

The oldest of the volcanic rock series are the andesite domes of northern Grenada which formed in the Miocene Period (26 to five million years ago). These andesite domes (Mount Alexander, Mount Rodney and Mount William) have been estimated to be 21 million years old. The andesite domes of Levera Hill and Sugar Loaf Island represent volcanic activity near the end of the Miocene Period. During this time, the first eruptions to the south occurred at the centers of South East Mountain and Mount Lebanon.

The Pliocene Period (five to two million years ago) witnessed the advent of Grenada’s most intense volcanic activity. In the south west of the island, basaltic lava flows estimated at 3.5 million years old are interlayered with reworked volcanic sediments. The source of the basaltic lava was probably the Mount Sinai Centre. Most of the deposits in southern Grenada are thought to be ‘lahar’ deposits of various ages ( a lahar is a massive mud slide from the side of volcanoes). The massive in-filling character of lahar deposits is thought to be responsible for the relatively subdued topography of southern Grenada.

In the northern central parts of the island, major eruptions recurred in the Pliocene Period and continued into the Pleistocene Period (two million to 10, 000 years ago). The island’s interior was the scene of intense activity as a series of eruptive centers shifted southward from Mount Granby towards Mount Qua Qua, emitting pyroclastic products and a series of basaltic and andesitic lavas. The final stages of this activity formed the andesitic dome summits of Fedon’Camp and Mount Qua Qua, and probably ended with the extrusion of basaltic lava on the western ridges of Mount Qua Qua.

The Mount St. Catherine massif represents the youngest major volcanic structure on the island. Activity at this center probably began in the Pliocene Period and continued throughout the Pleistocene Period. Initially, a vent near the Plaisance/Malagon area extruded basaltic lavas, which were overlain by a series of andesitic and diacidic lavas were deposited to the northwest of the present summit. The pyroclastic flows to the west of the present summit are the most voluminous deposits of their type on Grenada. The one and a half kilometer diameter crater to the southest of Mount St. Catherine (2,756ft) was partially filled in by an andesitic dome, which probably concluded the eruptions in the area.

The final stage of volcanic activity involved the formation of explosion craters throughout the island, most notably at what is now Lake Antoine. The Careanage in St. George’s and Grand Etang Lake. Lake Antoine is a well-preserved crater and has been described as the best example of a true “trufaceous ring” on the island. The Carenage in St. George’s and the Queen’s Park are both believed to be explosion craters, giving the island its best harbour and best source of scoria gravel. The three closely spaced explosion craters at Grant Etang are generally thought to be the youngest volcanic structures on the island, having formed approximately 12, 000 years ago.

In recent times, volcanic activity on the island has been virtually non-existent, with the minor exception of some hot springs which occur in the Mount St. Catherine area and emit sulphurous water and vapour. Other springs such as the River Salee and Peggy’s Whim Springs are not sulphurous to any extent.

About seven miles to the north of Grenada, however, is one of the most active volcanoes in the Lesser Antilles. It is a Diamond Island, a submarine volcano, 160 metres below sea level, known locally as “Kick em Jenny”. This derived from the French expression cay qu’ on gene, referring to the rough seas which normally surround it. It has erupted at least eight times this century, with the last eruption occurring in 1978. It is also possible that the volcano may emerge during its next eruption. Scientists in Trinidad and Tobago are currently monitoring this are for seismic disturbances, which might indicate renewed activity.

Carriacou and Petit Martinique, like other islands in the Grenadines, are exposed summits of volcanic peaks on a single narrow bank of submerged volcanic mountains. Carriacou lies 23 miles northeast of Grenada, separated by a channel 600 feet deep and Petit Martinique lies two and a-half miles northeast of Carriacou. The geology of Carriacou is two-third volcanic in origin and one third fossiliferous limestone (from Eocene and Pleistocene Periods). Erosion, uplift and faulting have all contributed to Carriacou’s varied topography. It is thought that the original volcanic activity formed Carriacou, Petit Martinique and the other Grenadine Islands in the late Oligocene Period (38 to 26 million years ago) and sank or were eroded away during the Pliocene Period, becoming completely submerged during the Pleistocene Period, Since that time, the regional uplifting of the sea floor has raised the island above sea level.