Juan Carlos Carracedo notified Bulletin editors that seismic activity in Tenerife during April and May 2004 was not followed by any volcanic activity. More than 200 earthquakes from magnitude 1 to 3 were recorded, but residents felt only three of them. Most of the epicenters were localized around the NW rift zone of Tenerife and in the strait between Gran Canaria and Tenerife. The crisis was probably related to dike emplacement at 3-4 km depth.

On 12 January 2005, an increase in unrest at Tenerife's Teide volcano over the previous 2 weeks was reported. Carbon dioxide emissions rose from 75 to 354 tons per day, and hydrogen sulfide emissions rose from 35 to 152 tons per day. Seismic activity remained elevated under the volcano. Fumaroles increased in pressure, and emitted sounds. No significant ground deformation was observed.

In a recent article in Eos, scientists from Spain and The Netherlands (Garcia et al., 2006), described a monitoring program for the Canary Islands. They noted that the Canary Islands started to show signs of seismo-volcanic activity at the end of 2003. In spring 2004, there was a significant increase in the number of seismic events (a mixture of regional, volcano-tectonic, and volcanic events such as tremor and long-period signals) located beneath Tenerife Island. The authors also noted an increase of fumarolic activity, an increase in carbon dioxide emissions in the NW part of the island, and changes in the gravimetric field on the N flank. After several seismic events had been felt by the population, the first alert level was declared by the civil protection division of the local government.

The volcano has a history of large eruptions destructive to populated areas. The authors reported that in 1992, the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) identified Teide, with its high-risk level, as one of the European Laboratory Volcanoes, thus receiving special consideration from the European Union concerning research proposals.

In the spring of 2005, the Spanish National Research Council (CSIC) initiated the TEGETEIDE project (Geophysical and Geodetic Techniques for the Study of the Teide-Pico Active Volcanic Area). It will monitor the seismicity of the volcano and include background noise analysis. The system's main goal is to detect precursors to a potentially dangerous eruptive episode at an early stage. The scheme is to use signals in both the time and the spectral domains.

References. Garcia, A., Vila, J., Ortiz, R., Macia, R., Sleeman, R., Marrero, J.M., Sanchez, N., Tarraga, M., Correig, A.M., 2006, Monitoring the reawakening of Canary Islands' Teide Volcano: EOS Transactions, American Geophysical Union, v. 87, no. 6, p. 61, 65.

Geological Summary. The large triangular island of Tenerife is composed of a complex of overlapping Miocene-to-Quaternary stratovolcanoes. The NE-trending Cordillera Dorsal volcanic massif joins the Las Cañadas volcano on the SW side of the island with older volcanoes, creating the largest volcanic complex of the Canary Islands. The origin of the 10 x 17 km Las Cañadas caldera, partially filled by the Teide stratovolcano, has been variably considered to be due to collapse following multiple major explosive eruptions or as a result of a massive landslide (in a manner similar to the earlier formation of the massive La Orotava and Guimar valleys), or a combination of the two processes. The most recent stage of activity beginning in the late Pleistocene included the construction of the Pico Viejo and Teide edifices. Tenerife was perhaps observed in eruption by Christopher Columbus, and several flank vents on the Canary Island's most active volcano have been active during historical time.

Information Contacts: Juan Carlos Carracedo, Estación Volcanológica de Canarias, Consejo Superior de Investigaciones Científicas (CSIC, Spanish National Research Council), Serrano, 117 28006, Madrid, Spain; Josep Vila, Departament d'Astronomia i Meteorologia, Universitat de Barcelona and Laboratori d'Estudis Geofísics "Eduard Fontserè," Institut d'Estudis Catalans, Barcelona, Spain.