Vigorous explosions occurred again on 8 and 16 January, causing widespread light ashfalls, but associated mudflows were smaller. Lava extrusion had resumed on 18 January and seismic evidence suggested that it was continuing on 21 January. Aerosols from the explosive activity have not yet been widely reported, but lidar instruments in Germany detected new material near the tropopause and aerosol layers were evident at sunrise over Colorado see Atmospheric Effects in Petrography of 15 December tephra.
Avalanche and lahar deposits emplaced December. Reconnaissance fieldwork on the N flank 26 December revealed thick deposits from a slush avalanche that appeared to have been triggered by pyroclastic flows, perhaps on 15 December. Scouring had occurred across the entire glacier where it was confined by valley walls, but only on the E half of its unconfined 3-km-wide lower portion. Water that apparently originated near the cloud-covered summit was flowing into the Drift River from a narrow channel eroded in the glacier.
The avalanche deposit was roughly 10 m thick at a sampling site about 1 km beyond the nose of the glacier, which extends roughly 8 km from the vent. The deposit was very massive, with no grading or vertical sorting evident, although contacts could be seen between individual flow units 3 of which were evident from the helicopter.
After emplacement, water had drained from the upper portion of the deposit, leaving noticeable air space between ice grains, and saturated the snowpack below the avalanche, which refroze into a zone of horizontally banded ice.
A sample from near the base of the avalanche had a bulk density of 1. Bulk densities of 2 samples from the porous upper portion of the deposit were only 0. Densities of the pyroclastic rock clasts ranged from 1. The avalanche had apparently been slushy during emplacement. Measurements of runup onto an older avalanche fan at a site 3.
Subsequent floodwaters eroded the distal portion of the slush avalanche and carried numerous large ice blocks as far as the mouth of the Drift River, forming levees that helped to confine later flows. Some of the stranded ice blocks, which reached many meters in diameter, were clear glacial ice, others were eroded pieces of the slush avalanche. The flood rafted ice blocks to 8 m above the riverbed and 1. Airphotos taken 16 December showed small lahars with lobate snouts that extended several kilometers down the SW side of the volcano.
However, patchy deposition occurred up to the crater rim, and the grooves were streaked with dark mud. Summit lava dome. About 21 December, a change in the character of local earthquakes and a slight increase in the number of small shocks suggested to geologists that magma might be approaching the surface.
Poor weather continued to obscure the vent area, although a vapor plume that reached 7. Seismic activity declined slightly on 24 December, but numerous small earthquakes continued to occur near the summit. An overflight 26 December revealed a large elongate lava dome that emerged from a vent at the N edge of the 1. Many hot rock avalanches cascaded down the dome's steep N side, generating small billowing ash clouds that rose m above the dome. The volcano continued to produce a vigorous vapor plume, primarily from the S side of the dome.
Summit glow was visible at night roughly 80 km E of the volcano on a low-light video camera at Kasilof. A slight increase in small earthquakes and rock avalanches near the summit during the next few days suggested an increased rate of lava extrusion. Ground and aerial surveys on 29 December confirmed significant additional growth of the dome, which was estimated from the air at roughly several hundred meters wide and twice as long. A vigorous gas plume that contained little ash rose 3.
The dome had grown further by 1 January, and AVO estimated its volume at roughly x 10 6 m 3. Strong explosions and mudflow, January. Shallow microearthquakes associated with the lava dome and deeper events centered km below the volcano began a rapid increase after a magnitude 1. By the next afternoon, seismic energy release had built to about the same level as immediately before the start of the eruption on 14 December. At on 2 January, AVO issued a statement noting the potential for partial collapse of the dome's unstable N flank, deposition of hot tephra onto the glacier with resulting flooding in the Drift River valley, and moderate to strong explosive activity.
The Drift River facility was promptly evacuated. Less than 2 hours later, a vigorous explosion at had the strongest seismic signal of the December-January eruption. Airplane pilots reported that the tephra column reached Ash moved NE in light wind, and minor ashfalls occurred at Anchorage. The FAA issued warnings to aircraft, and most airlines cancelled flights to and from Anchorage. Another large explosive episode was recorded at , and tephra was reported to 12 km altitude.
Smaller explosive episodes were recorded at about and on 3 January. During an AVO overflight between and on 3 January, a turbulent steam plume with only minor ash rose through weather clouds to Clouds obscured the summit area on 3 January, but overflights during better weather 2 days later showed that the dome had been removed along with a substantial part of the upper Drift Glacier. Seismic activity had declined to the lowest level since the eruption began and there was no seismic indication of renewed lava extrusion.
Pyroclastic flows during the 2 January activity generated a major mudflow that covered the entire active flood plain of the Drift River to the head of its delta, inundated the delta, and reached Cook Inlet, 32 km from the vent. An area of about 60 km 2 was affected. The pyroclastic flows incorporated large amounts of ice and snow, and were transforming into lahars by the time they reached m altitude, near the nose of the glacier.
The flow transported high-density, high-temperature dome rocks to the coast and carried ice blocks several meters in diameter that did not rise to the flow surface, indicating that it remained a fully developed debris flow. Boulders, more visible from the air at the lower end of the deposit, reached 4 m in diameter; many were still hot and generating small steam plumes on 3 January.
Water pushed aside by the debris flow inundated the area N of the main Drift River delta, forming a large lake. Ice jams formed at the mouths of small streams in that area, temporarily damming them.
Heavy deposition in its main channel diverted the Drift River into a stream with considerably less capacity Rust Slough S of the oil facility, protected on that side by neither dikes nor topography. Water and debris were then able to flow around the 4-m outer dike, crossed the facility's landing strip, damaged support structures, and shut off electricity, but did not overflow the 2.
The tanks were not damaged and no oil was spilled. Crews returned during daylight on 3 January to begin cleanup. The flooding at the Drift River facility forced the shutdown of 10 of the 12 Cook Inlet oil production platforms. Explosions and debris flows, January. Strong explosive activity resumed 8 January with vigorous episodes at and figure 4. No seismic precursor was noted, although the nearest seismic station, on the N flank, had been damaged in the 2 January eruption.
Within 30 minutes, plumes reached The FAA issued an advisory to aircraft, and some flights were cancelled. Ash fell on the flanks and on a broad sector to the E, beginning about noon at Kenai 80 km E of Redoubt. Only a dusting of ash fell on Kenai, but Kasilof, about 25 km to the S, received more than 0. More than 1 cm accumulated at Soldotna, between Kenai and Kasilof. By , satellite images showed that the plume, about km long and km wide, had detached from the volcano and extended nearly to Anchorage.
Overflights later that day revealed no major changes to the summit area. A plume that was mainly vapor rose to about 5 km altitude [see also research aircraft data in ]. The 8 January pyroclastic flows triggered a debris flow much smaller than that of 2 January, but with a peak discharge comparable to that of the 18 May mudflow from Mt. Helens in the N fork of the Toutle River. One or perhaps 2 pyroclastic flows continued in a relatively dry state to below m altitude on the glacier. Debris flow material was initially concentrated in a deep gully on the E side of Drift Glacier, then spilled NE across the floor of the Drift River valley figure 5 from The flow bifurcated around a small hill on the valley floor; the S lobe stopped abruptly, but the larger N lobe continued downvalley, transforming into a hyperconcentrated flow within 15 km of the vent.
It spilled through a breach in the moraine that enters the valley from the Drift River lobe of Double Glacier, and continued for another 5. Ultimately the flow became sediment-laden before stopping above the head of the Drift River fan. There was no noticeable impact on the channels downstream. After the 8 January activity, the main debris flow channel was stripped of ice down to about m altitude, and ice was only intermittently evident for the next couple of hundred meters.
A small explosive episode lasting roughly 15 minutes was recorded seismically on 11 January at No clear seismic precursor was detected, and poor weather prevented observations of the plume. Another brief eruption was reported at , and a pilot estimated that the steam and ash cloud reached Multi-layered weather clouds made plume identification difficult on satellite images. A minute explosive episode that began at on 16 January produced widespread ashfalls.
Pilots reported ash to 9 km altitude and satellite data indicated that the plume reached Ash then continued E toward Canada. Data from debris flow detection devices indicated that a water and debris flow occurred in the upper Drift River within about 20 minutes of the eruption's start. One device, placed on the 8 January debris flow deposit, was triggered but not destroyed, suggesting that the 16 January flow was smaller.
Considerable snow had accumulated on the Drift River flood plain since 8 January, and the flow continued to accumulate water as it continued downstream.
Although the flow volume was not large in comparison with earlier episodes, it was sufficient to cause some of the water in the Drift River to return to its old channel. Personnel at the Drift River oil facility reported that no flooding occurred there. Renewed lava extrusion, 18 January.
Aerial observations on 18 January between and revealed that a small lava dome was again growing in the vent [see also ]. A vigorous steam plume rose to about 5 km altitude. Seismicity the next day suggested that lava continued to be added to the new dome. Small seismic events on 19 January at and , each lasting minutes suggested vigorous venting that may have included some ash emission, but the activity was not witnessed.
Drift River oil facility. Concern about the potential for a major oil spill prompted the removal of most of the more than , barrels of oil that were stored in the Drift River facility's 7 tanks at the start of the eruption. Oil is transported by pipeline to the Drift River facility from 2 small coastal storage facilities not accessible to tankers that serve production platforms in Cook Inlet. Drainage of the Drift River tanks began about 10 January, and was expected to be completed about 20 January with the removal of a third tankerload of oil.
To avoid prolonged shutdown of Cook Inlet oil production, officials tentatively planned to leave the Drift River facility empty until a tanker is ready to load, quickly fill the Drift River tanks from the small coastal holding facilities, then immediately pump the oil into the waiting tanker.
Riehle, J. Janda and T. Rose and J. Vallance , Michigan Technological Univ; C. Month-old lava dome destroyed by strong explosions; 3rd, small dome removed by new explosions six days later.
AVO's detailed summary of the eruption through late January appears in the 13 February issue of EOS, accompanied by a second paper on satellite observation of the December plumes see References, below. Airfall tephra. Initial tephra studies suggest that airfall deposits have been relatively modest. One of the 15 December explosions generated pumiceous tephra, including fist-sized bombs that melted their way into the snow.
Other explosive episodes appeared to have been dominated by accretionary lapilli and fine lithic ash. Dimensions of the plume were measured with upward-looking lidar over the Kenai Peninsula The base of the plume was at about 3.
Lava extrusion and minor venting, mid January-mid February. A new lava dome was first seen during an overflight on 18 January, although seismic evidence suggested the onset of extrusion by 13 January, before the 16 January explosion. Vigorous vapor emission limited observations of the dome in late January, and growth was difficult to discern. Rockfalls off the dome were extensive, but no new lobes or fissures were evident. Additional breakage of the glacier that remained above the vent was indicated by new crevasses and ice avalanches into the crater.
Ice blocks descended in stairstep fashion toward the dome from a vertical icewall. Most of the vapor emission originated from the area between the ice and the dome, obscuring the near-dome region and the interaction between ice and lava.
A stream of meltwater flowed from the crater. A minor seismic event began at on 7 February and lasted for about 20 minutes, suggesting vigorous steam venting. It was detected only by the summit station, indicating that little if any ash was ejected. The dome appeared nearly unchanged during an overflight the next day. Shallow earthquake activity recorded near the summit increased 12 February, suggesting a higher rate of dome growth. A tremor-like episode on the seismic station nearest the summit began at on 13 February and lasted nearly 30 minutes.
The seismicity was probably associated with vigorous gas venting, perhaps including a little ash. Shallow summit-area seismicity declined somewhat that day, but remained elevated, as dome growth apparently continued. Explosive episode, 15 February. A spectacular display of lightning and thunder that lasted for about an hour awakened many people on the Kenai Peninsula. Satellite data 7 minutes after the onset of explosive activity showed a possible low-level pyroclastic flow or surge extending km from the crater on Redoubt's NW quadrant.
By , satellite images showed a plume extending about km SE with an average width of more than 70 km. Airline pilots reported ash to 12 km altitude in the Homer area roughly km SE of Redoubt and more than 1 cm of ash on Homer's airport runway. Anchorage's international airport remained open, but the FAA warned aircraft to avoid the area near the volcano.
Most personnel were evacuated from the Drift River oil facility, but the 4 remaining crew members reported an increased flow of silty water in both the Drift River and Rust Slough, a small-capacity stream W of the oil facility into which much of the Drift River's flow was diverted by earlier mudflow-induced channel changes. The seismic station nearest the summit was destroyed, presumably by lightning, but seismicity decreased to low levels on flank stations 18 minutes after the onset of the eruption.
Pyroclastic flows had swept across the glacier's Piedmont lobe, and had entered small, previously unaffected drainages. A pyroclastic surge had moved about m up the N wall of the steep canyon that leads from Redoubt's breached crater.
Flood deposits, slightly less extensive than those of 2 January, were primarily dark brown sediment, locally containing abundant m boulders. Water had flowed around an L-shaped levee on the upriver side of the oil facility, and a small amount of water had penetrated the containment dike protecting the southernmost of the facility's 7 storage tanks, but no oil was spilled. Aerial observations on 18 February showed that a small new dome, with a volume of less than 1 x 10 6 m 3 , had begun to grow in the vent area.
Explosive episode, 21 February. Another vigorous explosion occurred on 21 February, beginning at [] and lasting for about [12] minutes. Winds carried the plume rapidly NE, and by satellite images showed its front km from the volcano, where it was about 80 km wide.
Pilots reported that the base of the cloud was at about 7. Kienle, J. Scott , CVO; R. Repeated strong explosions separated by growth of small lava domes; details of 15 February pyroclastic flow, surge, and lahar deposits.
Strong explosions separated by periods of lava dome growth continued into March table 1. Frequent seismicity, centered on Redoubt from the surface to about 10 km depth, has continued since mid-December figure 6. Information about the 15 and 21 February explosive episodes supplements the initial reports in Table 1. Strong explosive episodes and periods of lava extrusion during Redoubt's eruption, modified extensively from the original table with data from Brantley See Alaska Volcano Observatory, , for a more detailed tabular summary of activity through January.
Explosive episode, 15 February; deposits and morphologic changes. Fieldwork after the episode revealed changes in the vent area, and pyroclastic flow, surge, and lahar deposits. The concentrically fissured icewall S of the vent appeared unchanged and remained steep. Steam from vigorous fumaroles obscured the vent area and the north gorge, a steep gully that had been cut into the upper Drift Glacier. Heavy ashfall had occurred over a broad area of the NNW to W flanks within km from the vent, and airfall tephra was also evident to km S and 20 km E to ENE of the vent.
On the NNW flank, snow avalanches or slush flows moved across snow-covered glaciers and into gullies W of those affected by earlier explosions. A sheet flood of slush flows traveled NE and E from the summit, entering the Drift River from a small valley E of Drift Glacier also unaffected by previous explosions.
A pyroclastic surge had spread N across the Drift Glacier to the crest of a steep ridge m above the glacier's toe. The deposit near the ridge crest, mm thick, was dominated by sand-sized andesite fragments with occasional pebble-sized grains. In a creek valley NE of the ridge, the deposit was coarser very angular, coarse sand-sized andesite grains and thicker mm. The deposit also included willow branches to 8 cm in diameter and 1. The surge was diverted eastward by the ridge, depositing dark material against another ridge km to the NE, in a zone from about to m altitude.
The base of this zone was about m above the valley floor. The surge destabilized snow on steep sides of S- and SW-facing valleys, triggering snow avalanches some ash-rich and slush flows. Drift Glacier was mantled by a deposit of poorly sorted, massive, pebbly, medium sand-sized, pyroclastic flow material.
The deposit ranged from a few centimeters thick on slopes to considerably more on flat areas, and appeared to be concentrated on the E half of the glacier. Flooding had wet the top cm of the deposit in gullies.
The glacier itself was much more deeply gullied than it had been after the 8 January explosion, with many large ice blocks partially detached from the glacier surface. The pyroclastic flow s and surge fed a mixed flood of water and pyroclastic debris that caused considerable erosion of the glacier and the banks of the Drift River W of the glacier's Piedmont Lobe.
Most of the debris was sand-sized, but included clasts some juvenile up to 1 m in diameter, plus clear ice from Drift Glacier and large amounts of snow from the glacier and valley. Hot andesitic dome rocks were found as much as 37 km from the dome 30 km from the glacier. The flow was apparently very water-rich for its entire length, which extended km from the glacier to the oil facility at the mouth of the Drift River.
Heights of overtopped banks suggested that the flow was 5 m or more deep in the gully on the E side of the glacier and was still m deep in the lower valley. A zone of snow blocks m wide marked flow margins. Flow characteristics were detailed from field evidence. Although the flow filled most portions of the valley from wall to wall, islands were left in wider sections, suggesting a maximum discharge less than that on 2 January.
Below the canyon mouth, some of the peak flow followed the old Drift River channel, but most went into Rust Slough, a relatively low-capacity stream. Muddy water from Rust Slough entered the oil facility roughly 4 hours after the onset of the eruptive episode, flooding a larger area than on 2 January, but caused no major damage.
Some water seeped through but did not flow over the southernmost tank's containment dike, and did no apparent damage. Small pyroclastic flows and dome growth, February. A pyroclastic flow moved about halfway down the Drift Glacier's north gorge on 15 February between about and An overflight on 18 February revealed that a small new lava dome was growing in the previously active vent.
Geologists observed another pyroclastic flow, triggered by dome collapse, that moved down the gorge on 20 February at A dark ash plume rose from the flow to about 3.
A similar but larger episode was seen from the Drift River oil facility at about , accompanied by a plume and lightning. Steaming pyroclastic flow deposits in the gorge extended to about m altitude, and fresh ash ENE of the vent, primarily from the early morning episode, lay on snow that had fallen February. An explosion that produced a large steam and ash plume accompanied by thunder and lightning began at and lasted for about 12 minutes.
Ash deposits appeared thick NE of the volcano. Both the Drift River and Rust Slough were bank-full before the activity began, but much less additional stream flow was generated by this explosive episode than on 15 February and only minor flooding resulted, without reported damage or injuries. The small dome that had been growing in the crater was partially destroyed by the explosion.
Some pyroclastic flow deposits were visible on the glacier near the gorge. Explosive episode, 24 February. Seismic stations near Redoubt began to record a strong signal associated with explosive activity at Seismicity had returned to background after minutes. A steam and ash column rose to about 9 km altitude, accompanied by thunder and lightning. Heavy weather clouds prevented observations by satellites, but ashfall was reported along a narrow zone extending NE from the volcano.
At the Beluga power plant km NE of Redoubt , the main power source for Anchorage, light ashfall began at about and heavy ashfall 30 minutes later.
All but one of its gas turbines were shut down to prevent damage. A second crest, at , flooded the S half of the oil facility's runway. Aerial observations revealed that another small lava dome had begun to grow in the active vent after the 24 February explosion. Explosive episode, 28 February. Seismic data indicated that explosive activity began at , continued at a relatively low level for about 10 minutes, paused, then resumed more vigorously at During the initial pulse, no ash rose above the tops of weather clouds at km altitude.
Ash was reported at 11 km altitude within 9 minutes of the onset of the much stronger second pulse. Satellite data showed a cloud about 25 km across extending ENE from Redoubt at , as ashfall was beginning on oil platforms in the Cook Inlet.
By , infrared imagery showed a cloud about km long and km wide moving rapidly ENE, nearly km from the volcano. A seismometer near the Drift River recorded 2 apparent flow events, the first associated with the initial pulse, the second, much larger, with the stronger second pulse. Significant flooding was anticipated for the lower Drift River, but instead, its flow declined somewhat.
During field work several days later, deposits from numerous pyroclastic flows were found on the Drift Glacier, some of which may have temporarily blocked the main N flank drainage channel on the glacier. Such blockage, if any, had ended by 4 March. Explosive episode, 4 March. A large explosive eruption occurred at An airplane pilot reported that the eruption cloud had reached about 12 km altitude 30 minutes after the onset of the activity.
The cloud moved N, and ashfall was reported about 30 km NNE of the volcano. Increased water flow, but no flooding, was reported from the Drift River oil facility. Explosive episode, 9 March. An explosion at ejected an ash-poor plume that reached about The explosion was slightly larger than those of 21, 24, and 28 February, and 4 March, but significantly smaller than the 15 December, 2 January, and 15 February episodes.
At , a satellite image showed a plume about 90 km across E-W , extending N and W from the volcano figure 7. Flooding occurred in the Drift River, and water flowed into small streams just to the S Rust Slough and Cannery Creek , but no water penetrated dikes protecting the Drift River oil facility.
The activity was preceded by a magnitude 5. Shallow seismicity remained elevated for hours after the explosion, then declined, but remained above background level. By the next day, a small dome was again being extruded from the summit vent, and seismic data indicated continued dome growth through 13 March.
Explosive episode, 14 March. Explosive activity began at , ejecting a plume to 12 km altitude that was also accompanied by lightning. There was little or no ash in the upper portion of the plume. Seismic data suggested that the explosion was slightly more vigorous than on 9 March, but the plumes appeared similar. Traces of ash were reported on the Kenai Peninsula and in the Anchorage area.
Satellite data at showed a plume moving ENE. Moderate flooding occurred in the lower Drift River, and some water was again diverted into Rust Slough and Cannery Creek. Water did not enter the oil facility, where 90, gallons of oil had leaked through a defective or open valve on 10 March. The oil had been confined by a containment dike, and most had been cleaned up by the time of the 14 March activity. Moderate explosions and dome extrusion; rootless phreatic explosion as eruptions interact with glaciers.
Quoted material is from the AVO staff. Information about the 4, 9, and 14 March explosive episodes supplements the initial reports in Since 15 February, explosive episodes have occurred at average intervals of days table 1. Explosive episodes were associated with pyroclastic flows and surges that triggered floods and lahars in the Drift River valley, which drains the volcano's N flank figure 8.
The summit seismometer that was damaged during the 15 February event was removed in March and three new seismometers were placed on the volcano's summit and flanks. Since early January, deposition in the Drift River's main channel has diverted significant amounts of flood water and debris into Rust Slough, S of the Drift River oil facility. An L-shaped 4-m-high levee upstream from the oil facility was designed to protect it from Drift River floods, but neither levees nor topography protect its S side.
Beginning on 4 March, deposition in Rust Slough has diverted floodwater farther southward into Cannery Creek, just upstream of the Drift River facility. None of the subsequent floods associated with March-mid April explosive episodes have affected the oil facility. Moderate flooding occurred in the Drift River. A new diversion upstream of the Drift River oil facility caused much of the flow to be diverted S of the facility from Rust Slough into Cannery Creek. Tephra fell primarily W of the volcano; Port Alsworth, 95 km SW of the volcano, received a light dusting from the southern margin of the plume.
Tephra fell E of the volcano; the Drift River oil facility reported heavy ashfall from to Oil facility crews were evacuated because of the heavy ashfall.
Winds were relatively light, and by , the plume extended less than km N and about km E of the volcano. They reported no changes in steam plume activity and did not hear any noises. However, 20 minutes later, they noted an approximate doubling of the Drift River's discharge 4 km downstream from the glacier.
The increased discharge was accompanied by large quantities of cobble-sized ice. The dome appeared to be growing slowly between observations. Explosive episode, 23 March. Seismic activity at the summit stations had increased around on 22 March and had stayed at elevated levels for most of the day.
Seismic activity then decreased several hours before the 23 March explosive episode. A plume was reported to Light ashfall was observed W of the mountain, but ash did not fall on any community.
Discharge increased in the Drift River. An image from the NOAA 11 polar orbiting satellite at figure 10 , 26 minutes after the onset of the explosive episode, showed a plume extending WNW from the volcano. The plume continued to move rapidly WNW, and by , The deposits were generally hot, dry, and friable; where they rested on snow, the basal part of thick deposits, and those less than 50 cm thick, were wet and warm to the touch.
Poor weather obscured observations of the summit area from 26 March until 6 April. Explosive episode, 29 March. An increase in discharge of the Drift River was reported, reaching the oil facility by Pilots reported a plume, consisting chiefly of steam, to 15 km. Tephra fallout appears to have been similar to that of 4 March; light ashfall was reported to km N-NE of the volcano.
Deposits from a debris flow or hyperconcentrated flow were observed in the upper valley and flooding appeared similar to 23 March. No hot debris or ice blocks were observed in the upper valley. Explosive episode, 6 April. An explosive event began at and was recorded for minutes at the Spurr station. Seismicity declined after the explosive event. An ash plume was reported to 9 km; wind shear caused the lower part of the plume to drift NW and the upper part to drift E.
The ash plume reached the W coast of the Kenai Peninsula by , but only light ashfall was reported in Kenai during the evening. Peak discharge attenuated quickly downvalley. Dome growth and hydrologic events April. This dome appeared to be larger when observed on 10 and 13 April and was greatly oversteepened on the N face. A flood of ice blocks up to 1 m across caused a 4-fold discharge increase in one of the large glacier canyons.
Repeated increases in discharge were noted over a minute observation period. An iceslide blocked the entire width of the canyon bottom upstream of the increased discharge area.
Episodic release through a tunnel at the base of the ice jam may explain the surges observed at the canyon mouth. A series of explosions migrated N and S of this area along a glacier bed stream, producing an elongate crater perhaps m long.
Numerous small pyroclastic flows emanated from the explosion area and formed a small pyroclastic flow fan that dammed the main water flow from the dome area for about an hour.
Explosive event, 15 April. The ash plume reached elevations between 9 and 12 km and the plume moved N-NW. There were no clearly identifiable seismic precursors. Seismic activity before and after the event appeared unchanged. Information about the 15 April explosive episode supplements the initial material in In general, seismic and explosive activity were at relatively low levels figure Intense steaming in the crater area coupled with poor weather have limited viewing of the dome and crater area to 5 observations during the report period.
The pattern of explosive eruptions every days that had characterized Redoubt's activity from 15 February to 21 April has changed; as of mid-May, the last significant explosive event had occurred on 21 April, 3. Explosive episode, 15 April. The explosive event triggered a pyroclastic flow down the N face of the volcano, and a mudflow that carried hot blocks of dense dome rock m in diameter 4 km downvalley to the E end of the Dumbbell Hills; figure Winds carried the tephra N-NW from Redoubt; flat discs of pumice up to 4 cm in diameter were noted about 10 km NW of the vent area.
Three cloud-to-ground lightning strikes were detected NW of the volcano. Explosive episode, 21 April. Additional photos and a bibliography are available on the Alaska Volcano Observatory homepage. Sturm, M. Redoubt on the flow of Drift Glacier, Alaska, U. Till, A. Geological Survey Bulletin , 19 p. Wood, C. Skip to main content. Toggle menu Go to search page. Search Field. You are here Home. Redoubt Volcano after the to eruptions. As of February 10, , the increased activity had continued, but the volcano had not yet erupted.
At that time, the Alaska Volcano Observatory warned of four possible outcomes: the volcano could quiet without an eruption; a small eruption could occur; a larger explosive eruption could occur; or the flank of the volcano could collapse in a massive landslide such as the one that occurred when Mount St. Helens erupted in Based on past activity at Redoubt, the Alaska Volcano Observatory expected a small to moderate eruption.
This image, taken by the Landsat satellite on August 16, , illustrates some of the potential hazards associated with an eruption. Even in late summer, the volcano was covered in snow.
As hot gases and lava erupt from the volcano, the snow will melt, possibly sending floods of water and debris down the mountain. These volcanic floods are called lahars, and a lahar from Redoubt would likely travel down the Drift River, which drains the volcano on the north. The volcanic flood could reach Cook Inlet, shown on the right side of the image. Such flooding on the Drift River is not unprecedented.
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