When musing about the Caribbean islands’ Volcanoes, a few names will pop up at once, like Soufriere Hills on Montserrat, Pelée mount in Martinique, Grande Soufrière in Guadeloupe and maybe Kick’em Jenny. The area being rife with volcanoes and the imagination of the early settlers being limited, some people will add Soufriere St Vincent and also maybe the one on St Lucia and its famous Pitons.
One island is in my mind under represented, and I’ll try to explain why.
A small riddle to begin : Which island can boast 9 potentially active volcanoes, a cold fumarolic zone plus several extended fumarolic fields including the world’s second largest boiling water lake ? Yes, this is Dominica.
It is located between the french islands of Martinique (to the south) and Guadeloupe (to the north).
It is a bit smaller than its neigbours (only 750 km2) and is much less populated (about 72 thousand people compared to the 386 and 405 thousands of Martinique and Guadeloupe). It is an independant state since 1978, and a former British dominion.
The topography of the island is very rugged.
The ubiquitous Columbus discovered the island on 3rd November 1493, a Sunday, hence the name. Speaking of imagination….
The Carib indians descendants or Kalinagos, which are the last living in the Caribbean, are still about 3000 strong and have their own territory and elected chief, prefer to call her “Wai‘tu kubuli” meaning “her body is tall”, which shows some sense of observation. Indeed, were it not for the Grande Soufrière on the nearby Basse Terre, Mount Diablotins, at 1447 m could have claimed the title for highest mountain of the Caribbean arc.
As with many islands in this region, Dominica’s history has seen a series of fierce rivalry between the British, the French, the Spanish and the Caribs, with the British winning in the end in this case. However, as the first settlers were of french descent, local Creole or Pidgin language is rather french based and a lot of locations bear french sounding names.
On a more broad geological point of vue, Dominica is part of the Caribbean arc, but shows some specificities.
First, it is the last of the windward islands, but also the first of the Leewards islands (according to Wikipedia). So it’s kindda in the middle. Choose for yourself.
Also this the last “single” island. Afterwards, the island chain divides to the north, with the eastward islands being mainly of sedimentary nature (Grande Terre, Marie Galante, Antigua, Barbuda….) and the westward islands being of Volcanic origin (Basse Terre, Montserrat, Redonda, St Kitts, Nevis, Saba).
Also and this is one of the main difference points, the island is the only one sporting several active (or potentially active) volcanic complexes on the same emerged part. If you check the other neighbour islands, there is the Grande Soufrière, Soufriere Hills, Mount Pelée, The Quill, but for each of these islands there is only one active volcanic complex. Unfortunately, very little is known of the submarine structures in the arc, except for Kick’em Jenny which has been quite studied, as recently as last year (see the Nautilus expedition for some spectacular footage – http://www.nautiluslive.org/).
Unsurprisingly, Dominica is nearly made entirely of volcanic rocks. Some exceptions exist, but are very limited in area and number. Contrary to the northern neighbor Marie Galante, which is called “La galette” due to its flat topography, and is made of sedimentary rocks.
Volcanic rocks from different geological area can be found since the Miocene. The oldest rocks date back to 6,92 Ma or possibly 13 Ma. Some volcanic centers stopped being active and suffered from erosion even as new volcanic areas were and are active.
There are also submarine volcanic domes which were identified to the north of the island to the south of Guadeloupe. The 2 domes which are referred as “Twin Peaks”, rise from 1000 m from the sea floor and the highest peak reaches 153 m below sea levek.
There is another smaller submarine dome some distance from the NW coast, over 700 m high and culminating at 550 m depth.
It is not known if these domes are potentially active.
About 1 Ma ago volcanic activity switched from the northern part of the island (with some residuals) to the south.
Six major volcanic centers were active since the Younger pleistocene to present.
Morne trois pitons, morne Watt, Wotten wave/Micotrin, Grand soufriere hills (again!), Morne anglais, and plat pays volcanic complex. Finally there is the Valley of desolation, a very active fumarolic fields in which you find the famous Boiling lake (to get there you need an 8 hour trek in the jungle). The boiling lake in a flooded fumarole at the bottom of a small lake (the total length is about 60 m in diameter)
The linguistically inclined have already noted that most of the places name sound french…because they are. Morne is a creole word meaning mount or hill. Piton is a peak, Plat Pays means flat land.
The most recent activity happened between 50 000 to 450 BP. All these centres have had some rather recent seismic activity, and together with Morne aux Diables and Morne Diablotins are considered potentially active centers.
Again I disgress to explains place’s names. Diables and Diablotins means devil and little devils. This does not refer to any surnatural creature but are just the names of now extinct birds, which fell prey to the first rats brought by the early settlers and to the settlers themselves.
They were described (including explanations on how to capture and cook them) by the famous Père Labat, a monk of the Dominican order, friend of the french flibustiers, who swashbuckled in all the Caribbean area between 1694 and 1705 and introduced the distilling rum still. A fiery 59° rum from Marie Galante is named in his honour. He made also some visit to the Soufrière of Guadeloupe which he described in his book.
Seismicity in Dominica
Earthquake swarms have been felt by the population since the early settlers.
Events were reported in 1765, 1841(North),1849,1893 (North), and 1937/1938.
Since 1953 and the installation of the first seismic network, there were swarms in 1959,1967,1971, 1976, 1985/86, 1994/95, 1997 and 1998/2000. There were some swarm in the north in 2000 and 2003.
Since 2000 the seismic background level seems to be higher.
In the south more than the majority of the swarms have been associated with the Morne Plat Pays Volcanic complex. Between 1998 and 2000 there were about 1500 earthquakes in that region and even if the frequency has diminished it is still more elevated that before the swarms onset. This swarm is rather shallow (2 to 6 km depth) and could be the result of magma repressurisation.
In the north, the Morne aux Diables and Morne Diablotin volcanic area has shown more than 500 events between 2000 and 2003.
Dominica is a destination of choice for the volcanically inclined. The island can boast several interesting or unique volcanic features and can provide very interesting excursions. Dominicans are a very friendly people and try to preserve their island from the evil of mass tourism. If some people are interested I can provide information on how to get there and who to contact.
Source Jan M. Lindsay, Alan L. Smith M. John Roobol and Mark V. Stasiuk Dominica, Chapter for Volcanic Hazards Atlas, http://www.uwiseismic.com/downloads/dominica_vha.pdf
Here are Matt´s riddles! This week the answers could be volcanoes, volcanic or geologic features.
1) The two images. Answer: Bishop Tuff, KarenZ, 2 points.
2) Holy Moses! Tiny Tim has a tomahawk and a walleye! Answer: Coso volcanic field. This field is in the China Lake Naval Air Weapons Station, which developed the Tomahawk, Tiny Tim, Walleye, and Holy Moses missiles. Sissel, 2 points.
3) The division of the Trinity. Answer: Rio Grande rift. The Trinity site, where the first nuclear bomb was detonated, is at the White Sands missile range in this rift. Talla and Bobbi, 1 point each.
4) It’s dot zero west of Denver. Answer: Dotsero volcano, a marr in Colorado, which erupted only about 4400 years ago! Inannamoon667, 2 points.
5) Pink Floyd and Luke’s father know where it is. It’s radioactive. Answer: Compton Belkovich thorium anomaly (This is a volcanic feature on the dark side of the moon, possibly a caldera. This is unusual, because almost all of the moon’s lavas are on the side facing earth. It was revealed because of the detection of thorium deposits. Someday, it might be a good place to mine rare-earth elements. Bobbi, 2 points.