HR: 1340h
AN: V53B-1543    [Abstracts]
TI: A Study of the 2450 BP Pululagua Plinian Eruption (Ecuador): Implications for Models of Tephra Dispersal
AU: * Volentik, A C
EM: avolenti@mail.usf.edu
AF: University of South Florida, SCA 528, Tampa, FL. 33620 United States
AU: Bonadonna, C
V53B-1543 AF: University of South Florida, SCA 528, Tampa, FL. 33620 United States
AU: Connor, C B
V53B-1543 AF: University of South Florida, SCA 528, Tampa, FL. 33620 United States
AU: Rosi, M
V53B-1543 AF: Universita di Pisa, Dipartimento di Scienze della Terra, Pisa, 56100 Italy
AU: Ruiz, G
V53B-1543 AF: Escuela Politecnica Nacional, Instituto Geofisico, Quito, 38053 Ecuador
AU: Connor, L J
V53B-1543 AF: University of South Florida, SCA 528, Tampa, FL. 33620 United States
AB: The 2450 BP Plinian eruption of Pululagua is known to have occurred in no-wind condition, resulting in circular-shape isopach and isopleth maps. Previous studies showed that the Plinian fallout is composed of 3 main units: the basal grey ash (BGA), the basal Plinian fallout (BF) and the white ash (WA). This study focuses on the BF unit, (consisting of three main layers: BF-I, BF-II and BF-III) and the co-Plinian unit (WA). The circularity displayed by Pululagua fallout was verified before sampling 23 locations along a south-east axis. Granulometry and componentry analysis have been performed on the collected samples throughout the usual sieving procedure. The fraction < 1.0Φ of each sample was also analysed using the Malvern PharmaVision 830 optical device. Results include: (1) grain-size distribution; (2) morphological parameters of each single particle, such as: (i) mean diameter; (ii) area; (iii) volume; (iv) roundness; (v) convexity and (vi) mean intensity; and (3) single image for each individual particle. Shape parameters such as roundness, convexity and mean intensity can be used as fingerprints of the sample material and could be a powerful tool for a fast componentry analysis of the volcanic ash. The absence of wind provides an ideal opportunity to calibrate models for tephra dispersal. Data from unit BD-II were therefore used to calibrate the model TEPHRA. An inversion technique also helped us determine crucial eruptive features, such as column height and volume. In addition, different techniques typically used to determine the distribution of maximum clasts were tested in the field. Resulting discrepancies significantly affect the derivation of important eruptive features (e.g. column height and wind speed).
DE: 0545 Modeling (4255)
DE: 0550 Model verification and validation
DE: 8404 Volcanoclastic deposits
DE: 8428 Explosive volcanism
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005