HR: 0800h
AN: V31B-0490    [Abstracts]
TI: Destruction of San Salvador Volcano and Birth of El Boquer\´{o}n Volcano (El Salvador): Detailed Stratigraphic Study of G1 and G2 Sequences.
AU: * Ferr\´{e}s, D
EM: dolomita70@gmail.com
AF: Instituto de Geof\´{i}sica, Universidad Nacional Aut\´{o}noma de M\´{e}xico, Ciudad Universitaria.Coyoac\´{a}n, M\´{e}xico, DF 04510, Mexico
AU: Delgado, H
EM: hugo@geofisica.unam.mx
AF: Instituto de Geof\´{i}sica, Universidad Nacional Aut\´{o}noma de M\´{e}xico, Ciudad Universitaria.Coyoac\´{a}n, M\´{e}xico, DF 04510, Mexico
AU: Hern\´{a}ndez, W
EM: whernandez@snet.gob.sv
AF: Servicio Nacional de Estudios Territoriales. Servicio Geol\´{o}gico Nacional., Ministerio de Medio Ambiente y Recursos Naturales de El Salvador. Instalaciones del ISTA., San Salvador, 00000, El Salvador
AU: Guti\´{e}rrez, E
EM: egutierrez@snet.gob.sv
AF: Servicio Nacional de Estudios Territoriales. Servicio Geol\´{o}gico Nacional., Ministerio de Medio Ambiente y Recursos Naturales de El Salvador. Instalaciones del ISTA., San Salvador, 00000, El Salvador
AB: San Salvador volcano (SSV) in Central America begins its formations ~70 kyrs. BP. Between 40 and 30 kyrs BP a large eruptive episode caused the collapse of the old stratovolcano and formation of an elliptic caldera (6 x 4.5 Km). Thereafter El Boquer\´{o}n (EBV) grew inside this caldera between 30 and 3 kyrs ago. In the last 3 kyrs, eruptive activity was concentrated on the northern sector of the volcanic complex. Eruptions were effusive and explosive from the central crater and from subsidiary cones (Sofield, 2001). The last eruption of EBV was in 1917. Fall and pyroclastic flow deposits (known as G1) were associated to the destruction of SSV, caldera formation and the birth of EBV. These dark grey dacitic deposits are distributed all around the volcanic edifice and have estimated volumes of 1.7-8 km3. They appear interbedded with Ilopango Caldera deposits and hence, their age is estimated to be less than 40 kyrs BP (Sofield, 2001). In our geological and stratigraphic work, a detailed characterization of G1 deposits was made through granulometric, modal and textural analysis, and revision of its chemical composition. In addition, this work reports for the first time a series of alternating fall and pyroclastic flow deposits in the upper levels of the sequence (similar to G1) interbedded with paleosoils. One of these fall deposits, called G2, has a wide distribution south and east of the volcanic edifice, and is currently under study. This sequence precedes the stratigraphic record of EBV. We report the volumes of G1 and G2 deposits and describe the alternation of the deposits between them. Finally, we try to explain if the collapse of the ancient SSV and the caldera formation was caused by the first of these events (G1) or it was the result of a series of events that produced different deposits (G1, G2 and the alternation of falls and flows between them) over a period of time. EBV is a very high\-risk volcano due to its proximity to the city of San Salvador, with 1.5 million inhabitants. This work will help to better establish hazards scenarios in order to produce volcanic hazard maps of EBV.
DE: 1105 Quaternary geochronology
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8440 Calderas
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting