USGS Update 2004-Nov-22 10:15
Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), coupled with eruption models, show that ash clouds that rise high above the crater rim today would drift southeastward.
Recent observations: The only field work conducted yesterday was continued construction on a new site west of the volcano to improve and strengthen our radio-telemetry network. Saturday’s field work during ideal conditions produced good sets of photographic, thermal-imaging, and gas-sensing data. The welt, the broad area of uplift south of the 1980-86 lava dome, has now reached the crater wall on the southeast and south and has also expanded to the southwest. It also appears to be moving northward into the southern part of the 1980-86 lava dome. The new lava dome, which lies within the welt, continues to expand upward and outward. The dome expansion is accompanied by growth of fractures creating weak zones. The steep west face of the dome is crumbling piecemeal, but, as fractures grow, there is an increasing chance of large slabs of hot rock toppling westward and forming ash clouds that drift out of the crater and hot avalanches, or pyroclastic flows. The flows would sweep over, erode, and melt snow and ice and produce lahars, or volcanic debris flows, that pour northward out of the crater onto the Pumice Plain. The three instrument packages, called Spiders, that were lowered from a helicopter into the crater on Saturday are operating well and sending back data in real time. The GPS site placed near the top of the new lava dome is moving at an impressive rate southeastward and upward. In 24 hours it moved about 10 meters (33 feet) southeastward and 2 meters (6.5 feet) upward, confirming visual and photographic observations. Gas measurements made on Saturday were of high quality and show that daily gas emissions remain at a more or less constant rate of a couple hundred tons of sulfur dioxide, about 1000 tons of carbon dioxide, and several tons of hydrogen sulfide.
Growth of the new lava dome inside the crater of Mount St. Helens continues, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. During such eruptions, episodic changes in the level of activity can occur over days to months. The eruption could also intensify suddenly or with little warning and produce explosions that cause hazardous conditions within several miles of the crater and farther downwind. Small lahars could suddenly descend the Toutle River if triggered by heavy rain or by interaction of hot rocks with snow and ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard along the river channel upstream.
Potential ash hazards to aviation: Under current eruptive conditions, small, short-lived explosions may produce ash clouds that exceed 30,000 feet in altitude. Ash from such events can travel 100 miles or more downwind.
The U.S. Geological Survey and the University of Washington continue to monitor the situation closely and will issue additional updates and changes in alert level as warranted.
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