HR: 09:00h
AN: V31B-05    [PDF]
TI: Hydrothermal disturbances at the Norris Geyser Basin, Yellowstone National Park (USA) in 2003
AU: * Lowenstern, J B
EM: jlwnstrn@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS 910, Menlo Park, CA 94025 United States
AU: Heasler, H
EM: Henry_Heasler@contractor.nps.gov
AF: Yellowstone National Park, YCR, Mammoth, WY 82190 United States
AU: Smith, R B
EM: rbsmith@mines.utah.edu
AF: University of Utah, Department of Geology and Geopysics, Salt Lake City, UT 84112 United States
AB: The Norris Geyser Basin in north-central Yellowstone National Park (YNP) experienced a series of notable changes during 2003, including formation of new hot springs and fumaroles, renewed activity of dormant geysers and elevated ground temperatures. This abstract provides a short synopsis of the new hydrothermal activity. In 2000, Yellowstone's tallest geyser, Steamboat, erupted after a dormant period of nearly 9 years. It erupted twice in 2002 and then again on 26 March and 27 April 2003. Surges in flux of thermal water preceding the eruptions (preplay) were recorded by a couplet of temperature data loggers placed in the outlet stream. The data indicated pulses of water flow with 1 and ~3 day intervals. On 10 July 2003, a new thermal feature was reported just west of Nymph Lake, ~ 3.5 km northwest of the Norris Museum. A linear series of vigorous fumaroles, about 75 m long had formed in a forested area, ~ 200 m up a hill on the lake's west shore. Fine particles of rock and mineral fragments coated nearby vegetation. Fumarole temperatures were around the local boiling temperature of water (92$\deg$C). After two months, somewhat reduced steam emission was accompanied by discharge of ~ 3-10 gallons per minute of near-neutral thermal water. Trees within 4 meters of the lineament were dead and were being slowly combusted. Porkchop Geyser in Norris' Back Basin had been dormant since it exploded in 1989, littering the nearby area with boulders up to over 1 m in diameter. Since that time, its water had remained well below the boiling temperature of water. From 1 April through 1 July `03, the temperature of waters in Porkchop's vent increased continuously from 67$\deg$ to 88$\deg$C. Each Summer, Norris' Back Basin experiences an "annual disturbance" where individual hot springs and geysers typically show anomalous boiling, and have measurable increases in turbidity, acidity and SO4/Cl ratios. The disturbance has been linked to depressurization of the hydrothermal system as the hydrostatic pressure of the snowmelt-fed groundwater table wanes each summer. This year, the "Norris disturbance" is estimated to have begun on 11 July 2003,when pronounced changes were noted, including thermal pools that were boiled to dryness (e.g., Pearl Geyser), creating fumaroles. Porkchop Geyser erupted for the first time since 1989 on 16 July. New mud pots formed along the Back Basin Trail and increased ground temperatures were noted over an 500 x 300 m area. Park staff noted temperatures up to 94$\deg$C at 1 cm beneath the ground surface in areas that were previously cool. Vegetation in the area immediately died and began to break down due to the high temperatures. Yellowstone National Park closed the Back Basin Trail to all visitor travel on 22 July 2003. During the first week of August 2003, the Yellowstone Volcano Observatory installed a temporary monitoring network in the Norris Geyser Basin. University of Utah staff, with equipment and personnel made available by IRIS, UNAVCO, USGS and YNP, installed seven broadband seismometers and five continuous GPS receivers. In addition, YNP deployed a series of temperature data-loggers to record changes in flow from thermal features within the Norris Back Basin. The network is intended to identify ground motions associated with fluid flow within the geyser basin that may accompany eruptions of geysers, boiling episodes or events precursory to hydrothermal explosions. The monitoring network will remain operational for between four and twelve weeks.
UR: http://volcanoes.usgs.gov/yvo
DE: 7280 Volcano seismology (8419)
DE: 8045 Role of fluids
DE: 8400 VOLCANOLOGY
DE: 8419 Eruption monitoring (7280)
DE: 8424 Hydrothermal systems (8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting