HR: 09:30h
AN: V31A-07 INVITED     [Abstracts]
TI: Collapse calderas
AU: * Aguirre-Diaz, G J
EM: ger@geociencias.unam.mx
AF: Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Campus UNAM Juriquilla, Queretaro, Qro 76230, Mexico
AU: Marti, J
EM: joan.marti@ija.csic.es
AF: Instituto de Ciencias de la Tierra Jaume Almera, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, 08028, Spain
AB: A collapse caldera is a volcanic explosive structure that forms during the collapse of crustal blocks on top of a shallow magma chamber. During this collapse, a large volume of magma is evacuated, first explosively, in the form of pyroclastic fallouts and pyroclastic flows, and then effusively, as lava domes or flows after collapse. The result is a catastrophic explosive volcanic collapse that forms a depression that could end with different shapes, circular, oval, rectangular, or irregular. Three main types of collapse calderas can be defined, 1) summit caldera, 2) classic caldera, and 3) graben caldera. Summit calderas are those formed at the top of large volcanoes and are related to relatively small-volume pyroclastic products that include plinian fallouts and ignimbrites, such as Crater Lake, Las Cañadas, and Somma-Vesuvio. Classic calderas are semi-circular to irregular-shaped large structures, several km in diameter that are related to relatively large-volume pyroclastic products including pumice fallouts and widespread ignimbrites, such as Long-Valley, Campi Flegrei, and Los Humeros. Graben calderas are explosive volcano-tectonic collapse structures from which large-volume, ignimbrite-forming eruptions occurred through several vents along the graben walls and the intra-graben block faults causing the collapse of the graben or of a sector of the graben. The main products of graben calderas are surge-deposits and large-volume widespread ignimbrite sheets. Pumice fallouts are practically absent. Examples include the Sierra Madre Occidental in Mexico, La Pacana (Andes), Catalan Pyrenees, and perhaps Scafell (United Kingdom). Any of the three caldera types mentioned above could have collapsed in three different ways, 1) piston, when the collapse occurs as a single crustal block; 2) trap-door, when collapse occurs unevenly along one side while the opposite side remains with no collapse; 3) piece-meal, when collapse occurs as broken pieces of the crust on top of the magma chamber.
DE: 8400 VOLCANOLOGY
DE: 8428 Explosive volcanism
DE: 8440 Calderas
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly