January Reconnaissance Trip

May/June Expedition

Press Release

LA REFORMA / TRES VIRGENES
 

GEOGRAPHIC AND CULTURAL SETTING      La Reforma caldera (right)/ Las Tres Virgenes volcano:  This collection of volcanoes lies between two major settlements in northern Baja California Sur; 35 km to the southeast is the port and mining town of Santa Rosalia (population 14,000), and 36 km to the southwest lies the oasis of San Ignacio (population 2,000).  At highest risk is Mexican Highway 1, the Transpeninsular Highway.  This main ground transportation corridor on the Baja peninsula crosses the south flank of the main cone, only 6 km from the summit, an area that was inundated by some of the youngest lavas and pyroclastic units from Volcan Las Tres Virgenes.  Future eruptions on the south flank of the cone would produce certain disruption of commercial and tourist traffic to and from the entire southern half of the peninsula.  Eruptions could pose a threat to air traffic, as major airlines currently fly directly over these regions enroute to tourist destinations in Baja California and mainland Mexico.  Las Tres Virgenes is also a wildlife preserve, and a designated World Biosphere Reserve, as it hosts rare plant and animal species.  The purpose of this ongoing study is to characterize and evaluate potential volcanic hazards that could endanger nearby communities and this important transportation corridor. DESCRIPTION OF REGION - GEOLOGIC SETTING      Volcan Las Tres Virgenes is a composite volcano that lies along the eastern side of the Baja California peninsula.  Its very youthful appearance, evidence for recent activity, and potential risk to the only transportation corridor along the Baja peninsula make it important to understand the hazards posed by a future eruption at this volcano.  Las Tres Virgenes volcano is the youngest volcano in a group of Quaternary eruptive centers lying in the Gulf Extensional province.  This grouping of volcanoes rims the Las Virgenes Valley and apparently youngs in a counterclockwise fashion according to Sawlan (1984).  The oldest of these is the La Reforma caldera along the Gulf Coast with one K-Ar age of 1.09 ± 0.12 ma on precaldera andesite.  This volcanism was followed by another caldera forming eruption in the Sierra El Aguajito (also called Sierra Santa Ana) and then by the sequential eruptions of El Viejo (dated by K-Ar at 0.44 ma, Lopez-Hernandez et al, 1993), El Azufre, and finally by Las Tres Virgenes (with possible eruptions in the 1746 and 1857).

(Photograph by Keith Sutter)