| Wotten Waven Caldera |
The Wotten Waven caldera was identified and named by Demange et al. (1985). The caldera, the margins of which are partially fault controlled, is elongated west southwest, parallel to the chain of Pelean volcanoes that parallel the southern margin of the Central Graben. It measures 7 km by 4.5 km. The Micotrin dome is located on its northeastern margin. The Wotten Waven caldera was inferred to have formed by the subsidence caused by the eruption of the Roseau Tuff (Sigurdsson 1972). The deposits belonging to the Roseau Tuff have been subdivided into three units (Demange et al. 1985).
Based on available 14C dates, the Plinian eruptions that produced the Roseau Tuff occurred over a >20,000 year period (46,000 to 26,380 years B.P.). As all of these dates are from Units 2 and 3, the eruption of Unit 1 must be prior to 46,000 years B.P. Within southern Dominica there are other ignimbrite sequences, which also give ages within this range suggesting that they may also be associated with the Plinian eruptions that produced the Wotten Waven caldera. The main outcrops of ignimbrites contemporaneous with the Roseau Tuff outside of the Wotten Waven-Roseau area include thick sequences on both the east coast in the vicinity of Grand Fond and Rosalie, and the south coast at Grand Bay. Recent eruptions from the Wotten Waven caldera produced small volume block and ash flow deposits and ignimbrites that have been dated at 1,160 and 1,020-1,050 years B.P. (Lindsay et al. 2005). These deposits, which are exposed in the northern part of the caldera, are interpreted to represent eruptions from the Micotrin domes, and from vents along |
|
A graben is a depressed block of land bordered by parallel faults.
A graben is the result of a block of land being downthrown producing a valley with a distinct scarp on each side. Grabens often occur side-by-side with horsts. Horst and graben structures are indicative of tensional forces and crustal stretching. Graben are produced from parallel normal faults, where the hanging wall is downthrown and the footwall is upthrown. The faults typically dip toward the center of the graben from both sides. Horsts are parallel blocks that remain between grabens, the bounding faults of a horst typically dip away from the center line of the horst.
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption.
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption.
An ignimbrite is the deposit of a pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere.
Ignimbrites are made of a very poorly sorted mixture of volcanic ash (or tuff when lithified) and pumice lapilli, commonly with scattered lithic fragments. The ash is composed of glass shards and crystal fragments. Ignimbrites may be loose and unconsolidated, or lithified (solidified) rock called lapilli-tuff. Ignimbrites form as the result of immense explosions of pyroclastic ash, lapilli and blocks flowing down the sides of volcanoes.
Open crater eruption, generally with high eruptive column that may collapse to produce flows and surges.
Plinian eruptions are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 (as described in a letter written by Pliny the Younger), which killed Pliny the Elder. Plinian eruptions are marked by columns of gas and volcanic ash extending high into the stratosphere, a high layer of the atmosphere. The key characteristics are ejection of large amount of pumice and very powerful continuous gas blast eruptions. Short eruptions can end in less than a day, but longer events can take several days to months. The amount of magma erupted can be so large that the top of the volcano may collapse, resulting in a caldera. Plinian eruptions are often accompanied by loud noises, such as those generated by Krakatoa. |
|
| Main Settlements in and Surrounding the Wotten Waven Caldera |
Laudat, Trafalgar, Morne Prosper, Wotten Waven, Roseau. |
| Recent Activity at the Wotten Waven Caldera |
For more information on this swarm, residents comments or if you have your own comments, please visit the earthquake section in our FORUM. |
|
| Photographs |
|
|
