HR: 1400h
AN: V33A-04    [Abstracts]
TI: Products and description from 3 phreatic eruptions occurred on March 2006. Poás Volcano, Costa Rica.
AU: Fernandez, E
EM: efernan@una.ac.cr
AF: OVSICORI-UNA Costa Rica, Campus Heredia Costa Rica, Heredia, 3000, Costa Rica
AU: * Duarte, E
EM: eduarte@una.ac.cr
AF: OVSICORI-UNA Costa Rica, Campus Heredia Costa Rica, Heredia, 3000, Costa Rica
AU: Saenz, W
EM: wsaenz@una.ac.cr
AF: OVSICORI-UNA Costa Rica, Campus Heredia Costa Rica, Heredia, 3000, Costa Rica
AB: After 1994 Poàs volcano resumed activity with a series of phreatic eruptions on march 2006. This work focuses on three main documented phreatic eruptions their characteristics and ejected products. On march 24, a strong eruption was emitted from the south part of the hot crater lake affecting the dome area. This phreatic eruption occurred around noon (18 hrs GMT) issuing an inclined column of water, sediments and pre-existent blocks towards the south of Laguna Caliente. The eruption was observed by several visitors from the crater lookout. They reported that a cypresoidal ejection issued from the lake surpassed the dome splashing acid water, sediments and blocks towards the dry area, south of the lake. Yet on Friday evening, a spray of acid water and fine sediments from the lake was produced. Next day staff from OVSICORI-UNA visited the east side of the volcano to confirm deposition of material charged with lake water, blocks and sediments from the east side of the lake. Impact craters were documented in one area ranging from 300 to 700m beyond the source point. The area visited showed a gray appearance although the rainy conditions accumulated small ponds of such sediments in crevices and lower drainages. The maximum reach of a single plume of fine sediments was approximately 5 km to the SW of the main crater, such material was tracked and collected along the vegetated massif. Samples collected were composed of preexistent solid material from the bottom of the lake heavily altered by the action of acid and hot conditions during the last 12 years. Some of the more friable samples consist of compacted sediments that have aggregated miscellaneous granulometries. Varied material from these two eruptions fell inside the main crater. Lastly on Sunday 26th evening, another jet-like water/sediment stream was ejected, this time towards the W. Scattered blocks from this eruption fell outside the west rim of the hot lake provoking several impact craters. This was the only eruption that impacted with a thick sheet of sediments and blocks the outer parts of the crater basin. Right after these events fieldwork was directed toward the documentation of deposits, ejected material and impact in the surroundings. This abstract will be accompanied by a poster depicting a number of hi-res digital photos taken during the documentation process. Detailed description of deposits and materials will be given.
UR: http:www.ovsicori.una.ac.cr
DE: 8404 Volcanoclastic deposits
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8419 Volcano monitoring (7280)
DE: 8486 Field relationships (1090, 3690)
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly