HR: 1340h
AN: V53B-1547    [Abstracts]
TI: Textural Characterization Of Scoria From Low Energy Strombolian Events At Villarrica Volcano: Preliminary Data From November 2004
AU: * Gurioli, L
EM: gurioli@hawaii.edu
AF: G&G/SOEST University of Hawaii, 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Houghton, B
EM: bhought@soest.hawaii.edu
AF: G&G/SOEST University of Hawaii, 1680 East-West Rd., Honolulu, HI 96822 United States
AU: Polacci, M
EM: polacci@ct.ingv.it
AF: INGV/Catania, Piazza Roma 2, Catania, 95123 Italy
AU: Harris, A
EM: harris@higp.hawaii.edu
AF: G&G/SOEST University of Hawaii, 1680 East-West Rd., Honolulu, HI 96822 United States
AB: During November 2004 a multidisciplinary experiment was deployed for a 10-days period at Villarrica Volcano (Chile). Activity since the 1984-85 eruption has consisted of continuous, passive degassing from a summit lava lake/vent and subordinate strombolian activity. During the experiment, a small lava lake was active within a 70-m-deep summit pit. Within the lake regular bubble bursting ejected fragments that rose and fell within the crater itself, together with splashing of lava onto the inner pit walls. Rarer, more energetic events emplaced scoria around the crater rim extending just a few 10's of meters from the pit rim. The limited dispersion of the products, confirm the low energy character of even these events. This report presents preliminary analyses of the textural features of the juvenile material ejected by the low energy strombolian events that occurred between November 8 and 17. We collected two sample suites of 100-to-300 clasts lying on fresh snow at the eastern and western sides of the crater area and within 50 m of the pit edge. Products included decimeter-sized bombs, scoria lapilli, centimeter-sized reticulites and coarse ash comprising fresh glassy shards. Bombs were rounded as well as elongated, and included spindle bombs and flattened spatter forms. Apart from the golden reticulites, all products were black and iridescent, with metallic surface lusters. We have completed density measurements on pyroclasts ranging from 2 to 7 cm in diameter. The juvenile population of the first (8 November) sample was dominated by scoria (65%) with vesicularities of 50-80%, with the remaining 35% comprising pumice/reticulite with vesicularities of 79-94%. The second (17 November) sample had a lower percentage of reticulite (less than 15% of the total sample) with vesicularities of 89-96%. The scoria in this sample had vesicularities of 41-81%. In general reticulite is characterized by rare large vesicles (up to 5 mm diameter) in a closely packed network of mostly spherical medium-to-small bubbles, with scarce phenocrysts (olivine and plagioclase) and clear microlite-free glass. In contrast the scoria fragments contained abundant phenocrysts and microphenocrysts (olivine and plagioclase) which increase in abundance with increasing density. Low and medium density scoria were typically characterized by a single large (cm-sized) rounded vesicle at their core, surrounded by abundant small vesicles. The high-density scoriae show a decrease in the abundance of small vesicles.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005