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[This abbreviated chronology is updated periodically; see Update for daily reports.
Time is local: Pacific daylight time until October 31 and Pacific standard time thereafter]
Weekly Summary Report, October 15-21, 2004:
- Seismicity remained at a low level.
- Slow extrusion of new dome continued, with broadening of the surrounding uplifted area.
- GPS measurements continued to indicate no deformation of the volcano's outer flanks.
- Poor weather Oct 17-19.
Notable field results from Thursday, October 21, 2004:
- Geological and thermal-imaging observations confirmed that both the area of uplift and the new lava extrusion had increased in size noticeably since last
seen on October 14. The area of uplift and intense deformation continues to spread southward and its margin neared the crater wall.
- About 1 foot of new snow with a light dusting of ash covered much of the uplift, except for the new lava extrusion, which steamed heavily. The new lava
extrusion, in the western part of the uplift, was about 270 m (900 ft) long by 80 m (250 ft) wide and 70 m (230 ft) high and had a volume of almost 2 million
cubic meters. Its maximum temperature was about 600 degrees Celsius (1,100 degrees F).
- Rock samples from the new lava extrusion were collected from a helicopter by using a bucket slung on a 100-ft line. The samples resembled typical Mount
St. Helens lava, called dacite. Further detailed analyses of the samples should help to answer questions about the character of the magma driving the
eruption and how it relates to lava erupted in the 1980s.
- A gas-sensing flight detected low levels of the volcanic gases carbon dioxide, sulfur dioxide, and hydrogen sulfide, which is consistent with magma
continuing to rise from depth.
- Test flights of the Unmanned Aerial Vehicles (UAVs), which will hopefully be used for monitoring the crater area in the future, were conducted yesterday
close to the U.S. Forest Service's Johnston Ridge Observatory.
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MSH04_aerial_crater_dome_uplift_from_east_10-20-04.jpg
Mount St. Helens crater, dome, and uplift with new growth, as seen from the east.
USGS Photograph taken on 20 October 2004, by Dave Schneider.
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Weekly Summary Report, October 22-28, 2004:
- Seismicity remained at a low level.
- Slow extrusion of the new dome continued, with broadening of the surrounding uplifted area.
- GPS measurements continued to indicate no deformation of the volcano's outer flanks.
- Poor weather Oct 22-23 and 25-26.
Notable field results from Wednesday, October 27, 2004:
- A new GPS station on the southern part of the new dome showed motion downward and to the southeast; a station near the summit of the old dome had
moved northward about 7 cm (3 in.) since October 20.
- Thermal imaging showed an elongate band of elevated surface temperature, locally as great as 775 degrees Celsius (1,420 deg F), along the west face of
the new dome coincident with the area of exposed newly extruded lava.
- Gas-emission rates measured yesterday were similar to recent previous measurements, namely about 250 tons per day SO2, 300 tons per day CO2, and
2 tons per day H2S.
- Samples of dome rock similar in appearance to the rock of the older dome were collected from two localities in the vicinity of the exposed new lava.
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MSH04_new_growth_closein_10-27-04.jpg
Mount St. Helens new growth, closein, from the west-northwest.
USGS Photograph taken on 27 October 2004, by David Wieprecht.
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Weekly Summary Report, October 29-November 4, 2004:
- Seismicity remained at a low level.
- Slow extrusion of new dome continued, with broadening of the surrounding uplifted area.
- GPS measurements continued to indicate no deformation of the volcano's outer flanks.
- Poor weather Oct 29-Nov 1.
- Daily Updates:
10-29,
10-30,
10-31,
11/1,
11/2,
11/3,
11/4
Notable field results from Thursday, November 4, 2004:
- Sulfur dioxide (SO2) emission rates continued to be low and consistent with previous measurements. No H2S) was detected. Ash in the steam plume
prevented an accurate measurement of CO2.
- The elongate new dome, which extends southward from the 1980-1986 dome, had undergone substantial vertical growth since October 27, extruding
upward by as much as 100 m (330 ft). Exposed rock faces had temperatures in the range 400-500 degrees Celsius (750-930 deg F), creating the
incandescence that could be seen from the north on clear nights. The new dacite lava contains visible crystals of plagioclase, hornblende and hypersthene.
These samples differ slightly from those collected on October 20 and 27 and also from lava erupted at Mount St. Helens in the 1980s, by virtue of their
slightly higher SiO2.
- The steep new faces on the dome generated small hot rockfalls and avalanches within the crater. The finer particulate from these deposits, which roiled
upward within the steam plume, rose to about 3,360 m (11,000 ft) altitude, or about 800 m (2,640 ft) above the crater rim. Consequently the south and
southwest flanks of the volcano received a notable dusting of ash. This localized ash poses no threat beyond the near slopes of the volcano.
- Most dome growth has been vertical, with only about 30 m (100 ft) of outward growth in some directions. The thick glacial ice that buttressed the south and
east sides of the dome remained largely intact.
- A continuous-monitoring GPS station north of the volcano at Johnston Ridge Observatory had moved to the south by about 2 cm (0.8 in.) since late
September or early October. This slow shift may reflect a depletion of magma in the subsurface at 5-10 km (3-6 mi) depth. To confirm this result, five new
GPS receivers were positioned around the volcano's flanks 5-10 km from the crater to better track changes in the deeper parts of the magmatic system.
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MSH04_new_growth_uplift_from_east_11-04-04.jpg
Mount St. Helens' new growth, from the east.
USGS Photograph taken on November 4, 2004, by David Wieprecht.
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Weekly Summary Report, November 5-11, 2004
- Seismicity remained at a low level.
- Slow extrusion of new dome continued, with broadening of the surrounding uplifted area.
- GPS measurements continued to indicate no deformation of the volcano's outer flanks.
- Daily Updates:
11/5,
11/6,
11/7,
11/8,
11/9,
11/10,
11/11
Notable field results from Wednesday, November 10, 2004:
- Strong winds made interpretation of gas data difficult.
- Good viewing conditions revealed continued growth of the lava dome. Estimated dimensions for the "welt"--the broad area of deformation--were about 600 m
(about 1970 feet) in diameter. The new lava dome, in the central and western parts of the welt, was about 400 by 180 m (1310 by 590 ft). The highest point
on the new lava dome was about 250 m (820 ft) above the former surface of the glacier that occupied that point in mid-September.
- Maximum surface temperatures on the new dome remained at about 700 degrees Celsius (1,300 deg F).
- GPS instruments on the welt showed rates of movement as great as several meters per day, while GPS instruments on the 1980-86 lava dome show
movements of up to 1-2 cm per day(less than one inch) northward, away from the growing welt and new dome.
- The latest estimated volume of the uplifted area and new lava dome from detailed analysis of aerial photographs taken on 4 November was about 20 million
cubic meters (26 million cubic yards). This compared with volumes of about 5 million cubic meters on 4 October and 12 million cubic meters on 13 October.
The apparent decrease in rate of volume change (7 million cubic meters in the earlier 9-day period versus 8 million cubic meters in the later 22-day period)
made no account for millions of cubic meters of glacier ice that have been removed from a large part of the area of uplift. Work continued to assess this
effect. The 20-million-cubic-meter volume of the new uplift and lava dome was by now more than 25 percent of the volume of the lava dome that grew in the
crater between 1980 and 1986.
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MSH04_aerial_crater_dome_from_north_11-07-04.jpg
Aerial view of Mount St. Helens' crater and lava dome, as seen from the north.
USGS Photograph taken on November 7, 2004, by John Pallister.
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Weekly Summary Report, November 12-18, 2004
- Seismicity remained at a low level.
- Slow extrusion of new dome continued, with broadening of the surrounding uplifted area.
- GPS measurements continued to indicate no deformation of the volcano's outer flanks.
- Suitable weather for the scheduling of field work proved elusive.
- Daily Updates:
11/12,
11/13,
11/14,
11/15,
11/16,
11/17,
11/18
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MSH04_new_growth_from_east_11-12-04.jpg
Mount St. Helens' new growth as seen from the east.
USGS Photograph taken on November 12, 2004, by Willie Scott.
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Weekly summary report, November 19-25, 2004:
- Seismicity remained at a low level. The average size of events increased slowly, into the M1.5 range, while the number of background events diminished. Slow extrusion of new lava continued, with increased flexure of glacial ice adjacent to it.
- GPS measurements continued to indicate no deformation of the volcano's outer flanks.
- Daily Updates:
11/19,
11/20,
11/21,
11/22,
11/23,
11/24,
11/25
Notable field results from November 20:
- The welt of deformed crater-floor material and glacial ice was pushed to the south crater wall by the growing lava extrusion.
- During this week, the "Elevator" GPS receiver, which sat atop the new dome, traveled south-southeast 46 cm per hour and upward about 6 cm hour, as it was carried along the advancing whaleback-like new lava extrusion.
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MSH04_closeup_top_new_growth_from_east_11-20-04.jpg
Closeup of Mount St. Helens' new growth, from the east.
USGS Photograph taken on November 20, 2004, by Dan Dzurisin.
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Weekly summary report, November 26-December 2, 2004:
- Seismicity remained at a generally low level. A smattering of larger earthquakes, in the range M2.5-M3.1, occurred November 27-30. These were located beneath the 1980-86 dome at shallow depth, as are most of the earthquakes associated with the ongoing eruption.
- Daily Updates:
11/26,
11/27,
11/28,
11/29,
11/30,
12/1,
12/2
Notable field results from November 29:
- The new lava and its surrounding uplifted welt pushed up against the south crater wall. The lava, a whaleback-shaped extrusion, increased sufficiently in height that it could be seen from the Johnston Ridge Observatory visitor center (JRO). As quoted from our public update that was posted the next day: "The whaleback is impressively smooth on its flanks. It owes its smooth elongate appearance to ongoing extrusion from a vent at its north end, adjacent to the south side of the 1980-86 dome. The lava emerges from the vent with enough strength that it can push earlier-extruded lava southward toward the crater wall."
- The FLIR infrared camera noted substantial temperature readings (upward of 400 degrees C) only on the southwest and west sides of the whaleback flow. Maximum reading was 500 degrees.
- A eulogy was given for "Elevator," the GPS receiver that was slung into the crater and set upon the new lava extrusion. It became a victim of gravity after eight days atop its lumbering lava steed. Although short-lived, ELE traveled south-southeast 87 m. Upward motion was 8 m. Data from this instrument package confirmed the dynamics of the extrusion and have since helped to constrain physical models of the eruptive process.
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MSH04_crater_dome_from_west_11-29-04.jpg
Mount St. Helens crater and dome, with new growth, from the west.
USGS Photograph taken on November 29, 2004, by Jim Vallance and Matt Logan.
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Weekly summary report, December 3-December 9, 2004:
- Seismically, this week was a repeat of last week in nearly every way. The earthquake counts remained low, with characteristic events of magnitude 1.5 occurring every 60-90 seconds. Like the previous week, several larger earthquakes again shook the crater floor. These events, in the range M2.5-2.9, occurred Dec 5-7.
- A notable finding was small displacement of a GPS receiver high on the volcano's southeast flank. Total deflection on Dec 9: about 4 cm (1.5 inches) southeast, or about 2 millimeters per day in the eighteen days since November 20. It is thought to result from the banking of new lava against the inner crater wall. (Road bridges about 100 feet long sag an inch or so in response to heavy traffic loads, although few big trucks haul magma.) It is a trifling amount when compared with the "bulge" of 1980s Mount St. Helens, which deformed at rates of 1-2 meters per day.
- No field work except equipment maintenance was undertaken December 3-9.
- Daily Updates:
12/3,
12/4,
12/5,
12/6,
12/7,
12/8,
12/9
Weekly summary report, December 10-December 16, 2004:
- Seismicity remained at a generally low level.
- Slow extrusion of new lava continued, with increased flexure of glacial ice adjacent to it. The budging of the new dome against the south crater wall persisted in the GPS record of very small displacement high on the volcano's southeast flank.
- GPS receivers on the 1980-86 dome have become nearly static (trifling motion). MID-9 station, near the new dome has been slowing its northeast advance.
- Daily Updates:
12/10,
12/11,
12/12,
12/13,
12/14,
12/15,
12/16
Notable field results from December 16:
- The new lava dome appeared larger and broader than when last seen by field observers. Its top was almost flat but with a lengthy north-trending crack, like a loaf of expanding french bread. Along the crack were sags, graben, and fissures. Ash was emitted intermittently from the cracks, although none of these emissions were vigorous, and the ash dissipated quickly.
Weekly summary report, December 17-December 23, 2004
- Previously mentioned deformation (Dec 3 and Dec 10 reports) high on the volcano's southeast flank had largely ceased by December 20.
- The MID-9 GPS station, adjacent to the new dome within the crater, had ceased its northeast motion by December 20 and begun slowly retreating southwestward and subsiding. Conceivably the station sits upon ground that is now being dragged southward by the extrusion instead of being pushed northward by uplift.
- Daily Updates:
12/17,
12/18,
12/19,
12/20,
12/21,
12/22,
12/23
Notable field results from December 17 and 23:
- (Dec 17) A gas-monitoring flight showed that SO2 was up slightly but still within the range of past readings. CO2 is exactly at its ongoing average emission of 1000 ton per day.
- (Dec 23) A damaged Spider (portable seismic and GPS station) was retrieved from the 1980-86 dome and another installed in its place.
Weekly summary report, December 24-December 28, 2004
- Seismicity continues at its characteristically low pace.
- The new dome continued to grow, as monitored by the Sugarbowl volcanocam. Distinctive cracks that formed on the carapace provided visual references to track the dome's southward expansion.
- No external deformation beyond the crater was recognizable from GPS receivers.
- No field work yet this week
- Daily Updates:
12/24,
12/25,
12/26,
12/27,
12/28,
12/29,
12/30
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