Paris, 27 February 2012
The Lesser Antilles: a volcanic arc with multiple risks
The Lesser Antilles arc(1), which is directly related to the plate boundary between the Caribbean and North American plates, is made up of numerous volcanic edifices of which at least twelve have been active in the past 10,000 years. Montagne Pelée, in Martinique, and La Soufrière, in Guadeloupe, are among these volcanoes. Although magma compositions and eruption styles vary all along the arc, eruptions are usually explosive. Major landslides (also known as 'collapses'(2)) can occur on the flanks of volcanoes, causing potential tidal waves when the debris avalanche enters the sea. Scientists have previously shown that volcanoes in the Lesser Antilles have suffered at least 52 flank collapses, 15 of which took place in the last 12,000 years. Around Montserrat, no less than 75% of the products emitted by the ongoing eruption of the volcano have flowed into the sea.
Drilling offshore to reconstruct eruption history and understand the risks
During the new IODP(3) campaign, scheduled from March 3 to April 17 2012, the team plans to drill ten boreholes (130 – 500 meters deep), at strategic spots around three sites that are representative of the main volcanic processes in the Lesser Antilles arc: Montserrat, Martinique and Dominica. By analyzing marine core samples collected in 2002 off the Lesser Antilles, the scientists discovered a larger number of eruptions than had been inferred from surveys carried out on land only (where eruption deposits are sometimes hidden or eroded). In addition to sediments and layers of volcanic ash that can be used to trace the volcanoes' history, the drilling will for the first time make it possible to collect samples of debris avalanche deposits, in an area where the frequency of collapses appears greater than elsewhere.
The campaign's objective is to achieve the most detailed reconstruction possible of the eruption history of the Lesser Antilles volcanoes by documenting the volcanic construction and destruction cycles. In particular, the scientists will attempt to better define the nature of volcanism during the first stages of volcanic edifice construction (chemical composition, production rate, explosiveness, role of construction compared with destruction), as well as the processes characterizing eruption activity and its migration along the Lesser Antilles arc. The aim is also to better understand the processes at work in debris avalanches and sediment dispersion in the ocean environment. This information will help to improve assessment of the hazards related to volcanic activity in the region.Members of the scientific team
Location of planned drilling sites. Core drilling (130-500 meters depth) will be carried out off Martinique, Dominica and Montserrat, in both debris avalanches and sediments and tephra (layers of volcanic ash).
Example of layers of tephra (volcanic ash) showing successive eruptions, in a marine sediment core sample collected off the Lesser Antilles (Caraval, N/O L'Atalante, March 2002)
Images of the Soufrière Hills volcano (Montserrat) taken on 31 May 2003 and 12 August 2003 (before and after the collapse of July 2003)
© Le Friant et al. 2009
Changes in submarine topography off the coast of Montserrat during the ongoing eruption of the Soufrière Hills volcano:
bathymetric data (depth of the seafloor) from successive surveys carried out in 1999, 2002, and 2005 during various oceanographic campaigns, used to monitor the deposition of material that flowed into the sea during the eruption. The color scale shows the thickness of the deposits laid down from 1999 to 2002 (a), and from 2002 to 2005 (b).
1 - As opposed to the Greater Antilles, the Lesser Antilles is an archipelago made up of the southernmost islands in the Antilles, from the Anegada Trench to the north of the South American subcontinent. Guadeloupe and Martinique are part of the Lesser Antilles.
2 - The collapse is a result of various processes: injection of magma that fails to reach the surface, weakening of the flank by hydrothermal alteration, and fracture or overload caused by the edifice.
3 - The Integrated Ocean Drilling Program (IODP) is an ambitious project in which France, along with 17 other countries, plays a major part via the European ECORD consortium.
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