Volume No. 1 Issue No. 101 - Friday May 18, 2007|
The history and pictures of Dominica's volcanoes
By Thomson Fontaine
Nine of the Caribbean�s sixteen active volcanoes are located on the island of Dominica. By contrast there is one each on Guadeloupe, Martinique, St. Lucia, St. Vincent, Montserrat, Saba, St. Eustacius, St. Kitts, and Nevis. There are two in Grenada.
Dominica�s nine active volcanoes are ; Morne au Diable, Morne Trois Pitons, Morne Diablotins, Morne Watts, Morne Anglais, Wotten Waven Caldera, Valley of Desolation, Grande Soufriere Hills and Morne Plat Pays.
The youngest dated volcanic deposits on the island are associated with the Morne Patates dome on the flanks of the large active Plat Pays Volcano that comprises the southwestern end of the island. This was a Pelean eruption (similar to the eruptions of Mt. Pelee on Martinique in 1902 and 1929) and radiocarbon ages from the block and ash deposits suggest it occurred about 500 year ago.
In addition there have been two steam explosions (phreatic activity) in the Valley of Desolation in 1880 and 1997. Frequent seismic swarms and vigorous and widespread geothermal activity today characterize the island. In fact it is the most worrying of all the Caribbean volcanic areas and there is a general feeling that it (like Montserrat pre-1995) is long overdue for an eruption. Scientists are predicting that there will be at least one major eruption within the next 100 years.
What is of particular concern is that the capital Roseau and most of the islands infrastructure lie on a pyroclastic flow fan derived from the Wotten Waven caldera situated on the eastern outskirts of the capital.
The pyroclastic deposits of the Roseau area abound with ignimbrites (pumiceous pyroclastic flows), surge and airfall deposits with radiocaron ages ranging from 38,000 to 1000 years B.P.
Volcanologist Haraldur Sigurdsson as long ago as 1972 described one of the units which he called the Roseau ash and together with other workers traced its submarine extension. As a result of this work they concluded that about 38,000 years ago the island erupted around 56 cubic kilometers of pumiceous materials in what was described as the largest eruption in past 200,000 years in the Caribbean.
Pyroclastic flows deposited about 30 cubic km on the Caribbean floor and the remainder was deposited on the Atlantic floor from AntiTrade Wind dispersal. More recent work suggests that there are several ignimbrite sheets separated by ancient soils and the deposits may have resulted from several eruptions. However all conclusions indicate that the capital Roseau is situated in one of the most hazardous areas of the island.
The Dominican.net will bring you the history and photos of this aspect of our beautiful island over the next several issues. We begin by looking at Morne Plat Pays.
The cloud-capped summit of Morne Plat Pays stratovolcano lies on the horizon near the southern tip of the island of Dominica beyond the sprawling capital city of Roseau. This volcano has been active throughout the Holocene (last 10 ,000 years).
Three post-caldera lava domes (left-center to right) were formed north of a large arcuate depression open to Soufriere Bay on the west that formed about 39,000 years ago. This depression cuts the south west side of Morne Plat Pays stratovolcano and extends to the southern tip of Dominica. At least a dozen small post-caldera lava domes were emplaced within and outside this depression, including one submarine dome south of Scotts Head.
The latest dated eruption at the Morne Plat Pays volcanic complex occurred from the Morne Patates lava dome about 1270 AD, although younger deposits have not yet been dated.
The Morne Plat Pays complex is the site of extensive fumarolic activity, and at least ten swarms of small-magnitude earthquakes, none associated with eruptive activity, have occurred since 1765 at Morne Patates.
The History of a Volcanic Island