VOLCANICITY OF GUADELOUPE - HISTORICAL ACTIVITY -THE VOLCANIC RISK IN GUADELOUPE - FUTURE SCENARIOS

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Geological history of Soufrière

The volcanic island of Basse-Terre, which forms part of Guadeloupe, consists of 7 main volcanic fields each one including several eruptive centers. The current state of our knowledge indicates that only the Grande Découverte¬-Soufrière massif has been active in the last 10 000 years of the Holocene period.

This massif is characterized by a great diversity of eruptive products associating various styles of eruption which have shaped for 200 000 years a landscape geologically complex and morphologically very contrasting.

History of the Soufrière massif

The volcanic complex of the Grande Découverte¬-Soufrière massif consists of several volcanic buildings: Grande Découverte, Carmichaël, Amic, Soufrière, Echelle and Citerne.
The most recent magmatic activity generated the formation of the dome of Soufrière approximately 465 years ago (1440 AD). The volcano of Soufrière is the only active volcano of Guadeloupe (currently at rest between eruptions).

The reconstruction of the eruptive history of the Grande Découverte-Soufrière (GDS) composite volcano since the beginning of the activity approximately 200000 years ago has revealed very contrasting types of eruptions and their associated deposits. This evidence has defined three main phases:

200 000 to 42 000 years: "phase Grande Découverte"

The first, or phase Grande Découverte", corresponds to the construction of the principal structure. It is located on the southern side of the pitons of Bouillante and of Sans Toucher composite volcano. This first phase results in an alternation between effusive lava and pyroclastic episodes.

It ends in the installation of important pumice deposits of several km3 known as 'Pintade'. It also formed the Grande Découverte caldera from which we only see the remainder northern section.

42 000 to 11 500 years: "Carmichaël phase"

During the phase "Carmichaël", a succession of lava flows, domes formation and voluminous pyroclastic flow deposits, in particular 15 to 20,000 years ago, formed a new composite volcano in the caldera.

A first destabilization of side, without implication of magma, will partly destroy Carmichaël 11,500 years ago producing an avalanche of debris which will reach the sea towards the SO.

From 8 500 years to current days: "phase Soufrière"

The phase "Soufrière" begins 8500 years ago by a slope-collapse event of a new volcanic building erected in the south of Carmichaël. This generates the formation of a horseshoe shape crater directed south-south-west inside wich a new building will be built. This sequence construction-destabilization will be repeated several times with a particular destabilization 3100 years ago associated with a laterally directed magmatic explosion (pyroclastic blast) which destroyed approximately 60-100 km2 of the S-SO massif. Following this destabilization, the Amic dome was formed in the horseshoe shape crater. The scoria cones and associated lava flow fields of L‘Echelle and La Citerne were built on the sides of the Grande Découverte-Soufrière (GDS) composite volcano approximately 2,000 years ago. The last destabilization took place 465 years ago (1440 AD/- 100 years) at the time of the last explosive magmatic eruption of Soufrière which ended in the formation of the current dome.

This eruption generated andesitic pumice/scoria fallout deposit and the installation of pyroclastic flows in the radial valleys of the dome at approximately 5 km of distance.

In the last 15,000 years at least 7 eruptions with dome produced pyroclastic flows of low volume. Over this same period, the Grande Découverte¬-Soufrière massif was affected by at least 9 slope-collapse event whose products were set up mainly at the south-south-west sometimes reaching the sea (Boudon et al, 1988; Komorowski et al, 2005).

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