Multiparameter monitoring of Fogo Island, Cape Verde, for volcanic risk mitigation

Fogo Island in the Cape Verde Archipelago (North Atlantic) is a stratovolcano of nearly conical shape that rises 2829 m above sea level and 6000 m above the surrounding seafloor. With a population of 40 000, the island has known intense historical volcanic activity since AD 1500, with an average interval between eruptions of the order of 20 years. Twentieth-century rates were more subdued, with only two flank eruptions in 1951 and 1995. Following the 1995 eruption, increased awareness of the volcanic hazard affecting the population of the island led to the deployment of the permanent VIGIL Network. Seismographic stations (both broadband and short-period), tiltmeters and a CO2 sensor where installed in Fogo, together with a telemetry infrastructure to allow remote real-time monitoring. A broadband seismographic station was installed in neighbour Brava Island. The operation of the network was complemented by the introduction of routine geodetic and microgravity surveying and the operation of an automatic meteorological station. In this paper, we describe the methodology adopted to monitor the volcanic activity, combining real-time data analysis (volcanotectonic and volcanic earthquakes, volcanic tremor and tilt) with repeated surveying at intervals of several months (GPS, microgravity). Examples of data from the first years of operation are presented. In particular, the data pertaining to a period of anomalous activity in September–October 2000 are discussed, in the context of the risk mitigation strategy currently being developed