Cascade Range Current Update

Mount St. Helens Alert Level Change

Past Alert Level: Volcano Alert (Alert Level 3); aviation color code RED
New Alert Level: Volcano Advisory (Alert Level 2); aviation color code ORANGE

October 6, 2004 9:15 A.M., PDT

Following yesterday morning’s steam-and-ash eruption, seismicity dropped to a low level and has remained low. Low-level tremor observed following the eruption is also gradually declining. Lack of earthquake and rockfall signals suggest that deformation of the uplift area on the south side of the 1980-86 lava dome has slowed. Brief visual observations this morning from Coldwater Visitor Center showed weak steam emissions from the crater. We infer that the vigorous unrest of the past few days has lessened and that the probability of an imminent eruption that would endanger life and property is significantly less than at any time since Saturday, October 2, when the alert level was raised to Volcano Alert (Level 3). Therefore, we are lowering the alert level to Volcano Advisory (Alert Level 2).

Such decreases in the level of unrest, which may reflect a decrease in the rate of magma movement, have been common at Mount St. Helens during eruptions in 1980-86 and also at similar volcanoes elsewhere. Episodic changes in level of unrest over periods of days to weeks, or even months, are possible. We don’t think that the current episode of unrest is over and we expect fluctuations in the level of unrest to continue during coming days and months. Everyone should be aware that escalation in unrest and perhaps an eruption could occur suddenly or with very little warning. There may be little time to raise the Alert Level before a hazardous event occurs. Therefore, we continue to monitor the situation closely and will issue additional updates and changes in Alert Level as warranted.


Mount St. Helens Update, October 6, 2004, 7:00 a.m, PDT

Current status is Volcano Alert (Alert Level 3); aviation color code RED

Seismicity overnight has remained at very low levels. After the vigourous steam-and-ash emission of yesterday morning, seismicity dropped with individual events becoming smaller. By about 5 p.m. PDT yesterday, individual events became rare and as of 11:00 p.m., seismicity has been stable at a low level.

Yesterday, field crews continued to harden GPS sites for the approaching winter and retrieved data. The GPS sites on the dome survived the steam-and-ash emission and data are being received and processed at the observatory. The station on the northern flank of the dome, shows a trend of northward displacement totaling 2 cm in the last three days. This is the same sense of movement recorded by the nearby station that was destroyed by the first steam-and-ash emission on 1 October. Data from the other two stations on the dome, which were installed on 4 October are currently being analyzed. Data from GPS instruments on the outer flanks of the volcano show no movement of the outer flanks.

No gas measurements were made yesterday. A seismic crew installed an additional broadband seismometer on the northwest flank of the volcano which will help show a broader range of seismic energy release. With the help of the U.S. Forest Service, field crews installed an antenna mast for a VSAT uplink which will improve our ability to retrieve data from the field.

It began raining t the mountain at about 7:30 p.m. PDT. By about 9:30 p.m. about 0.1 inch of rain had fallen. Overnight, the acoustic flow monitoror (AFM) in the crater indicated that several small debris flows had moved past the site. By midnight, higher flows were recorded at a station on the pumice plain, but none were large enough to trigger an automatic alert. We expect these types of flowage events to recur during intense rainstorms.

Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), combined with eruption models, show winds this morning are from the west-southwest such that any ash clouds will drift to the east-northeast.

We continue to monitor the situation closely and will issue additional updates and Alert Level changes as warranted.

Press conferences will continue to be held at the Headquarters office of the Gifford Pinchot National Forest. The morning press conference is at 9:30 AM. If activity remains low, we will do a show-and-tell of some of the instruments were are using to monitor the volcano at the press conference.



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