|
|
November 1, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues.
- Although considered less likely at this time, the current eruptive activity could evolve into a more explosive phase that affects areas farther from the volcano and sends significant ash thousands of feet above the crater where it could be a hazard to aircraft and to downwind communities.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift at variable directions from the volcano, depending on altitude. Low altitude winds would carry ash clouds northeastward, whereas high altitude winds would carry ash clouds southeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Crews did not go the field yesterday because of inclement weather. No field work is planned for today.
November 2, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift northeastward from the volcano.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Crews did not go the field yesterday because of inclement weather. No field work is planned for today.
November 3, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift south to east-southeast with increasing plume height.
- Visibility was excellent at 7:00 a.m. and likely will remain so throughout the day. A steam plume will probably be visible as it rises passively and then drifts southward at crater-rim altitude. Some casual observers erroneously describe this plume as ash, although it rarely contains notable ash. Those needing accurate ash reports should consult the sources listed at the foot of this update.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Crews did not go the field yesterday because of inclement weather. No field work is planned for today.
November 4, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift southwestward to south-southwestward.
- Visibility is excellent and likely will remain so throughout the day. A steam plume is rising passively and drifting southwestward over the crater rim. The plume occasionally contains minor ash, which falls out in the crater and on the southwest flank of the volcano, darkening the new snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Crews are already in the field and will remain throughout the day. Planned work includes thermal-imaging and geological observations, collection of samples of dome lava and ash, slinging a new GPS station onto the 1980-86 dome, and taking photographs for use in determining growth rate of the uplift and new lava dome.
November 5, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift westward to southwestward.
- Visibility is excellent and likely will remain so throughout the day. A steam plume is rising passively and drifting south and southwestward over the crater rim. The plume occasionally contains minor ash, which falls out in the crater and on the southern flank of the volcano, darkening the new snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Crews were in the field yesterday, the first opportunity following a spate of inclement weather. Their findings:
- Sulfur dioxide (SO2) emission rates continue to be low and consistent with previous measurements. No hydrogen sulfide (H2S) was detected. Ash in the steam plume prevented an accurate measurement of carbon dioxide (CO2).
- The elongated new dome, which extends southward from the 1980-1986 dome, has undergone substantial vertical growth since October 27. A new mass of dacite has extruded upward by as much as 100 m. Exposed rock faces have temperatures in the range 400-500 degrees Celsius, creating the incandescence that may be seen from the north on clear nights. Field crews conducted geologic observation flights in the crater. To collect samples they landed a helicopter on the new dome for the second time in two weeks. The new dacite lava contains visible crystals of plagioclase, hornblende and hypersthene. These samples are similar to those collected on October 27 and also to lava erupted at Mount St. Helens in the 1980s.
- The steep new faces on the dome are generating small hot rockfalls and avalanches within the crater. The finer particulate from these deposits roils upward within the steam plume, rising to about 11,000 ft altitude, or about 2,600 ft above the crater rim. Consequently the south and southwest flank of the volcano have 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 of outward growth in some directions. The thick glacial ice that forms a buttress on the south and east sides of the dome remains largely intact. All dome growth is contained within the Mount St. Helens crater.
- A continuous GPS station north of the volcano at Johnston Ridge Observatory has moved to the south by about 2 cm since late September or early October. This slow shift may reflect a depletion of magma in the subsurface at 5-10 km 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. Two additional units will be deployed today.
November 6, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift eastward.
- Visibility is excellent and likely will remain so throughout the day. A steam plume is rising passively and drifting over the crater rim. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Yesterday field crews accomplished several missions. A seismometer and a GPS unit were installed on the 1980-86 lava dome to replace instruments destroyed in the explosion of October 1. The seismometer will improve the accuracy of earthquake locations and the GPS unit will track any deformation of the old dome. An array of two microphones was also deployed to aid in detecting explosions. Two benchmarks on and beyond the outer flanks of the volcano were reoccupied by GPS instruments as part of an effort to assess whether or not pressure changes have occurred in the deep parts (3 to 6 miles) of the magmatic system. Crews also carried out maintenance on several field sites. Day- and night-time photographs of the crater were taken from a site near Johnston Ridge Observatory. These will be compared with photographs taken from this same site during the past 6 weeks to assess changes on both the old and new lava domes and the crater walls.
November 7, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift northeastward to east-northeastward depending on their altitude.
- Visibility is excellent and likely will remain so throughout the day. A steam plume is rising passively and drifting northward out of the crater. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Yesterday field crews carried out maintenance on several field sites.
November 8, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift northward to northeastward depending on their altitude.
- Visibility is excellent and likely will remain so throughout the day. A steam plume is rising passively and drifting northward out of the crater. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Aerial observations yesterday showed that the new dome continues to expand and move upward. Small aprons of rockfall debris are accumulating at several sites around the new dome. Some ash emissions may be caused by these rockfalls as collapsing hot dome lava disintegrates into smaller fragments. No field investigations are planned for today.
November 9, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise above the crater rim today would drift northward to northeastward depending on their altitude.
- This morning’s images on the VolcanoCam show that a steam plume is rising passively and drifting northward out of the crater. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- The latest estimate of the volume of the uplifted area and new lava dome from detailed analysis of aerial photographs taken on 4 November is about 20 million cubic meters (26 million cubic yards). This compares 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) doesn’t take into account millions of cubic meters of glacier ice that have been removed from a large part of the area of uplift. Work is underway to assess this effect. The 20-million-cubic-meter volume of the new uplift and lava dome is now more than 25% of the volume of the lava dome that grew in the crater between 1980 and 1986.
- Today’s field work includes retrieval of GPS instruments from drive-to sites and routine maintenance and measurements at several stream gages.
November 10, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift northwestward.
- This morning’s images on the VolcanoCam show that a steam plume is rising passively and drifting southwestward out of the crater (distinct from the high-altitude wind conditions mentioned previously). The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- The latest estimate of the volume of the uplifted area and new lava dome from detailed analysis of aerial photographs taken on 4 November is about 20 million cubic meters (26 million cubic yards). This compares 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) doesn’t take into account millions of cubic meters of glacier ice that have been removed from a large part of the area of uplift. Work is underway to assess this effect. The 20-million-cubic-meter volume of the new uplift and lava dome is now more than 25% of the volume of the lava dome that grew in the crater between 1980 and 1986.
- Today’s field work includes retrieval of GPS instruments from drive-to sites on the south flank of the volcano. Flights for gas monitoring and crater observations, including infrared imaging, are also planned but are weather dependent. The current weather, high clouds, provides workable conditions.
November 11, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift west-northwestward.
- Clear views this morning show that a steam plume is rising passively and drifting westward out of the crater. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Yesterday field crews repaired the DomeCam, the time-lapse camera that is aimed at the new lava dome from a site near the crater mouth, and conducted visual and thermal-imaging observations and a gas-sensing flight. Strong winds made interpretation of gas data difficult. Good viewing conditions revealed continued growth of the lava dome. Current estimates are that the welt, the broad area of deformation, is about 600 m (about 1950 feet) in diameter. The new lava dome, which occupies the central and western parts of the welt, is about 400 by 180 m (1300 by 600 feet). The highest point on the new lava dome is about 250 m (820 feet) above the former surface of the glacier that occupied that point in mid-September. Maximum surface temperatures on the new dome remain at about 700 degrees C (1300 degrees F). GPS instruments on the welt show rates of movement of up to several meters per day, while GPS instruments on the 1980-86 lava dome show movements of up to 1-2 cm (less than one inch) per day northward, away from the growing welt and new dome.
November 12, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift west to northwest.
- Clear views this morning show that a steam plume is rising passively to about the height of the crater rim. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent extrusive rate calculations, about 4 cubic meters per second, are diminished slightly from those seen in mid-October. This change is small and does not indicate a notable change in the eruptive process. These rates, which are based on the volume of deformed crater floor and the amount of airborne sulfur dioxide (SO2) measured during gas-monitoring flights, have uncertainties associated with their calculation. Volcanoes like Mount St. Helens are expected to undergo slight variations in their extrusion rates during eruptive cycles.
- Crews are expected to be in the field today. Conditions permitting, a new GPS receiver will be lowered onto the new dome in order to monitor the uplift there. Photogrammetry and gas-monitoring flights are also scheduled.
November 13, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift eastward to northeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Visual observations yesterday confirm the continued growth of the new lava dome. Comparison of yesterday’s photographs with those of 10 November shows evidence of at least several meters of upward growth. A technique using laser-ranging binoculars from the helicopter to measure the position of points on the new dome was tested successfully yesterday. Repeat measurements should provide good control on future rates of change. Data from yesterday’s gas-sensing flight are still being evaluated, but suggest that gas emissions are slightly higher than those earlier in the week.
November 14, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift eastward to northeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Incandescence from the dome was visible overnight on the U.S. Forest Service webcam. At dawn this morning, the steam plume was rising lazily from the crater floor and barely cresting the rim, where it drifts southwestward and westward a short distance before dissipating. The plume may occasionally contain minor ash, which will fall out in the crater and on the flank of the volcano, darkening the snow.
November 15, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift prominently northeastward as a new weather front moves into the region.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- No direct visual observations are possible today, owing to a change in weather that brings rain and, at higher altitudes, snow to Mount St. Helens.
November 16, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift prominently northeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. Overnight, three earthquakes in the range M2.5-2.8 shook the crater floor. Although slightly larger than seen recently, they represent nothing unusual in the expected sequence of events for dome growth. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- No direct visual observations were possible yesterday, owing to a change in weather that brought rain and, at higher altitudes, snow to Mount St. Helens. The weather outlook is equally damp today. No field work close to the volcano has been undertaken since November 12. Instrumental monitoring is conducted “around the clock.”
November 17, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift east-northeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface. Since Monday night, the crater floor has been shaken by as many as eight earthquakes greater than magnitude 2 and as large as mag-2.8. Although slightly larger than seen recently, they represent nothing unusual in the expected growth of a lava dome, a complex process that varies slightly on a day-to-day or week-to-week basis. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- The volcano webcam this morning shows a clear view to the crater, although low clouds are gathering. The steam plume that rises from the dome is drifting northeastward. Weather permitting, field crews will try to complete missions that include gas monitoring, photogrammetry, and FLIR-camera infrared monitoring. An attempt will be made to recover and replace, by helicopter slingline, a defective GPS receiver that was installed on the new dome.
November 18, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift northeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- The volcano webcam this morning shows a foggy day, with snow level recently down to abut 2,000 ft. Views of the mountain are obscured at this time. Yesterday’s field crews were skunked by increasing clouds.
November 19, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- The volcano webcam this morning lives in a world of fog. Views of the mountain are obscured. During this past week, the task of getting crews to the field in suitable flying weather has been like trying to mix oil and vinegar. We’ll try again tomorrow.
November 20, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Today, after several days of poor weather, excellent conditions are permitting a host of field operations. Thermal-imaging and geologic observations have just started and are having the clearest views of the crater, uplift, and new lava dome since 12 November. Other plans include a gas-sensing flight, maintenance, data downloading, and, if conditions allow, helicopter-slinging of one or more instrument packages (a.k.a. Spiders) to both the 1980-86 and new lava domes.
November 21, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southward this morning and southeastward this afternoon.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Yesterday’s clear, calm weather, coupled with a relatively low level of steaming, created ideal conditions for observations and instrument installations. Thermal-imaging and geologic observations revealed further expansion of the welt, the broad area of uplift south of the 1980-86 lava dome, toward the southeast and development of several deep pits on the uplift that may be the result of melting of blocks of glacier ice and collapse of overlying debris. Three instrument packages called Spiders, two with GPS instruments and one with a seismometer, were lowered from a helicopter. One GPS sits near the top of the new lava dome. Processing of the first several hours of data, showed that the highest point on the new lava dome is at an altitude of 2256 m (7400 ft), or about 76 m (250 ft) higher than the summit of the 1980-86 lava dome. Hopefully this instrument can survive in its harsh environment and allow us to track movement of that point in real-time, both horizontally and vertically. This will provide a method for assessing how lava-dome growth is progressing. The new seismometer is located on the upper east side of the old lava dome and will help in obtaining better locations of earthquakes. Data from the gas-sensing flight is still being evaluated. Other work included aerial photography and construction of a new radio repeater site to ensure a more robust system for relating data to the observatory. The only field work planned for today is further work on the new repeater site.
November 22, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- 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.
November 23, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Field work and visual observations were impossible yesterday owing to poor weather. Early this morning, a few VolcanoCam images showed the usual night-time glow, but a low overcast will probably limit viewing today. The new GPS Spider that sits atop the new lava dome continues to move southeastward at a rate of about 10 meters (33 feet) per day, reflecting continued expansion of the dome. The other newly installed Spiders with GPS and seismic sensors are operating well. Numerous photographs of the crater and lava dome taken on Saturday (20 November) are available on the CVO website.
November 24, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southeastward early in the day and eastward later.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Field work and visual observations were impossible yesterday owing to poor weather. Today’s weather doesn’t look much better. The GPS Spider on the new lava dome continues its movement east-southeastward and upward, from which we infer that the growth of the lava dome continues much as is has in the past few weeks.
November 25, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift eastward early in the day and east-southeastward later.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Field work and visual observations were again impossible yesterday owing to poor weather. A high freezing level and periods of rainfall overnight increased flows in streams draining the crater, but were not sufficient to generate lahars. Strong winds accompanying the rainfall increased the background-noise level on many seismometers around the volcano.
November 26, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift east-southeastward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Field work and visual observations were again impossible yesterday owing to poor weather. The DomeCam, which sits northeast of the mouth of the crater, recorded a few partly clear glimpses into the crater this morning. These views show continued growth of the upper part of the new lava dome, consistent with data from GPS instruments on and near the new dome. We hope to take advantage of good weather on Sunday or Monday to get in the field for a variety of activities.
November 27, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southeastward this morning and southward later in the day.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Late afternoon aerial views show that growth of the welt and lava dome continue. Most of the east arm of the crater glacier that is adjacent to the welt is now deformed. Ice close to the welt is steeply inclined and intensely fractured; farther away the ice surface is beginning to rumple into broad ridges as the welt grows eastward. A magnitude 3.1 earthquake occurred at a shallow level in the crater about 5 a.m. this morning--the first earthquake greater than M3 that has been recorded since the new lava dome emerged in mid-October. It appears to be a larger version of the small earthquakes that have been occurring for many weeks at the rate of about one per minute. We hope to take advantage of good weather on Sunday or Monday to get in the field for a variety of activities.
November 28, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southward.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: This morning’s views from the U.S. Forest Service’s VolcanoCam show a freshly snow-covered volcano, blue sky, and a small steam plume rising from the new lava dome and drifting over the south crater rim. Tomorrow we plan a full day in the field to conduct a variety of observations.
November 29, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift southward early in the day and eastward later.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: Three earthquakes between magnitude 2.6 and 2.8 occurred last evening and early this morning amidst the ongoing sequence of smaller (mostly less than M1.5) earthquakes. Along with Saturday’s M3.1 event and similar-sized earthquakes that occurred in mid-November, they represent nothing unusual in the expected sequence of events accompanying lava-dome growth. A full slate of field work is underway today. Hopefully the approaching rain and snow will hold back until tonight. Winds are calm and there is very little steaming, so conditions are ideal for various types of activities. Thermal- imaging and gas-sensing measurements, visual and photographic observations, collection of ash samples from the volcano’s outer flanks, and repairs to communications systems are all planned.
November 30, 2004:
- Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
- Growth of the new lava dome inside the crater of Mount St. Helens continues and is accompanied by intermittent emissions of steam and ash.
- Wind forecasts show that ash clouds that rise high above the crater rim today would drift east-southeastward early in the day and south-southeastward later.
- Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
- Recent observations: A variety of field activities, including thermal-imaging measurements, visual and photographic observations, and collection of ash samples from the volcano’s south flank, were conducted yesterday under nearly ideal conditions. The only snag was lingering fog in the Tualatin Valley that prohibited launching of the gas-sensing flight. Several excellent photographs posted on our web site show the new lava dome within the welt, or broad area of uplift, in the southern part of the crater. The dome owes its smooth elongate appearance to ongoing extrusion from a vent at its north end, which lies at the south margin of the lava dome that grew between 1980 and 1986. The lava emerges from the vent with enough strength that it can push earlier-extruded lava southward toward the crater wall. The leading edge of the extrusion has now reached the crater wall, so it will be interesting to see what happens over coming days. Will new lava start to well upward over the vent and piggyback on the south side of the 1980s dome rather than continue to push against the buttress provided by the crater wall? Or will new lava move eastward or westward in a pattern similar to its southward movement? As in previous days, a few larger earthquakes of about magnitude 2.5 occurred amidst the ongoing sequence of smaller (mostly less than M1.5) earthquakes. Such a pattern represents nothing unusual in the expected sequence of events accompanying lava-dome growth.
|
|
