HR: 1400h
AN: V33A-10    [Abstracts]
TI: A Qualitative Estimate of the Volcanic Hazard
AU: * DE LA CRUZ-REYNA, S
EM: sdelacrr@geofisica.unam.mx
AF: Instituto de Geofisica Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico, D.F 04510, Mexico
AU: MENDOZA-ROSAS, A T
EM: ateresa@geofisica.unam.mx
AF: Posgrado en Ciencias de la Tierra, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico, D.F 04510, Mexico
AB: Volcanic hazard is defined in terms of the probabilities of occurrence of eruptions and their potentially destructive manifestations. These probabilities may be estimated analyzing the sequence of past eruptions in a given volcano, characterizing the eruptions by size and assuming that the impact and effects of an eruption are proportional to both, the energy (magnitude) and the rate of energy release (intensity). A quantity that characterizes eruptions based on those parameters is the Volcanic Explosivity Index (VEI, Newhall and Self, 1982). Here, we introduce an extension of the definition of volcanic hazard in terms of the expected annual release of energy by eruptions in each VEI category. This concept is based on the averaging property of a large group of volcanoes to release in a given time interval the same amount of energy in each VEI category. This means that a set of volcanoes tend to produce a larger number of smaller eruptions and a smaller amount of larger eruptions in such a way that in the given time interval, the numerous smaller eruptions release about the same energy than the few larger eruptions (De la Cruz-Reyna, 1991). The annual rate at which energy is released by eruptions in different VEI categories is described by log(EmKm) = b M + a, where Em is the energy released by eruptions in the VEI magnitude class M, and Km is the rate at which such eruptions occur. The parameters a and b depend on the eruptive history of individual volcanoes. The slope b determines the preferred mode of the volcano to release energy: through smaller (negative slope) or through larger (positive slope) eruptions, and the parameter a determines the energy potential of the volcano. We applied this method to analyze three active polygenetic Mexican volcanoes: Colima, Citlaltepetl and Popocatepetl. The former has the largest energy potential, although the slope b has a slightly negative trend suggesting that while large and very large eruptions may occur, the volcano shows a trend to release its energy by frequent smaller eruptions. Popocatepetl and Citlatepetl show smaller energy potentials than Colima and almost flat slopes, indicating a trend to release energy by eruptions of any size, but at lower rates. De la Cruz-Reyna S (1991) Bull Volc 54, 57; Newhall CG, Self S (1982) J Geoph Res 87, 1231
DE: 8404 Volcanoclastic deposits
DE: 8419 Volcano monitoring (7280)
DE: 8428 Explosive volcanism
DE: 8486 Field relationships (1090, 3690)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly