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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos

Comunicações orais ► em encontros internacionais


Referência Bibliográfica

ALFAMA, V., QUEIROZ, G., FERREIRA, T. (2010) - Geological Hazards in Brava Island and their Implications on Emergency Planning. MAKAVOLK 2010. Cabo Verde, 4 a 9 de Dezembro de 2010 (Comunicação Oral).


Brava is the westernmost island of the Sotavento group, in the Cape Verde archipelago. The later is located in a stable intraplate area, where is considered to exist a mantle plume or other deep mantle processes. As a consequence, some islands, particularly Brava, are affected by seismic activity and have recent and/or historical volcanic eruptions.


Despite the fact that Brava's historical records show no volcanic eruptions, it is possible to identify some recent eruptive centres and products (possibly Holocenic). These indicate that the corresponding volcanic systems remain active (Machado, 1965; Machado et al, 1968). Furthermore, some of these deposits have been formed through explosive eruptions, which points towards the possibility of a significant volcanic hazard.


The most significant seismic activity in the archipelago has been registered in Brava island region, often as seismic swarms of volcano or tectonic origin. The most important recent seismic crises occurred (1) between December 1980 and May 1981, where a maximum intensity of VII (Modified Mercalli Scale) has been registered; and (2) in June 2006 and January 2007. Also, the seismic activity associated with many Fogo island eruptions was felt on Brava as it happened during the 1951 and 1995 volcanic eruptions. However, the absence of a seismic monitoring network with an appropriate coverage of the archipelago prevents an adequate study on the location of the seismogenic areas.


Another significant geological hazard in Brava results from landslides triggered by seismic and volcanic activities, or by intense rainfall. Landslide scars have been identified on the slopes around the island as well as within river valleys on the western and southern areas of the island. In addition, strong evidences of gravitational instability have been reported on the sea cliff north of Baía da Fajã de Água, which suggest potential collapse.


Taking into account the geological hazards that can impact Brava Island a multi-hazard study is being conducted for their assessment. This will allow evaluating the susceptibility of Brava Island to each hazard, a key information for emergency planning and crises management as well as for land use planning. The integration of all the results will be done in a Geographical Information Systems in order to produce tools that can be used by civil protection authorities.