Westdahl

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  • United States
  • Alaska
  • Stratovolcano?
  • 1992 CE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 54.518°N
  • 164.65°W

  • 1654 m
    5425 ft

  • 311340
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

Most Recent Bulletin Report: January 1992 (BGVN 17:01)


Eruption apparently ends; seismic data from eruption onset

Westdahl's eruption appears to have stopped. Poor weather limited observations and the stop date is uncertain, but a significant decrease in eruption intensity was noted on 15 January. Geologists noted that comparison with the 1978 eruption suggested that this cessation in activity may be only a pause.

No plume penetrated the cloud deck that obscured the summit-area fissure during a 23 January overflight. The lava flow appears to have widened to cover 2-3 times its 3 December area (figure 5), while its front had not advanced significantly. As of late January, infrared images from the NOAA-11 polar orbiting weather satellite indicated a "warm" spot in the vicinity of the volcano. Exact registration of the warm area has been difficult, but it is believed to be associated with the position of the cooling lava flow. The FAA removed all flight restrictions around the volcano on 7 February. During aerial observations by FWS personnel on 13 February, only scattered steaming was noted from the flow. Minor steaming occurred from a small cinder cone near a steep, ice-walled canyon, where the fissure vent cuts the E part of the summit glacier.

Information Contacts: AVO.

The Global Volcanism Program has no Weekly Reports available for Westdahl.

Index of Bulletin Reports


Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

01/1978 (SEAN 03:01) Large new explosive eruption

02/1978 (SEAN 03:02) Major ash eruption (about six days)

05/1978 (SEAN 03:05) February ashfall on vessel 1,000 km SE of Westdahl

09/1978 (SEAN 03:09) February eruption site visited; new crater 1.5 km in diameter and 0.5 km deep

02/1979 (SEAN 04:02) 8-km cloud seen on satellite imagery

11/1991 (BGVN 16:11) Lava flows and tephra from 8-km NE-flank fissure

12/1991 (BGVN 16:12) Tephra emission declines

01/1992 (BGVN 17:01) Eruption apparently ends; seismic data from eruption onset




Bulletin Reports

All information contained in these reports is preliminary and subject to change.


01/1978 (SEAN 03:01) Large new explosive eruption

The USCG reported on 6 February that ash, accompanied by a sulfur odor, was falling on a station located at the foot of Westdahl. Lightning was observed above the summit, accompanied by thunder and rumbling. The summit is not visible from the Coast Guard station and cloud cover has prevented direct aerial observation of the group of volcanoes which includes stratovolcanoes Westdahl and Pogromni, active in historical time. However, Reeve Aleutian Airways personnel report an ash cloud rising to 8-10 km altitude, including some large blocks visible above the 3-km cloud layer. Satellite images returned 5 February show a well-developed ash cloud, but it has not yet been possible to pinpoint the eruption start time [see 3:9].

Information Contacts: T. Miller, USGS, Anchorage.

02/1978 (SEAN 03:02) Major ash eruption (about six days)

Data from satellite imagery and aircraft observations established that the eruption originated from the summit of Westdahl, one of five volcanoes on Unimak Island active in historical times. The eruption column was first visible in 5 February satellite imagery (figure 1), but Coast Guard personnel from Scotch Cap (15 km SW of Westdahl's summit) noted a sulfur odor during the evening of the 3rd and reported that ash had begun to fall by the next morning. Eruption column height was estimated at 8-10 km from aircraft observations on 6 February (figure 2) and up to 8 km from interpretation of satellite imagery (figure 3). Nearly 1 m of ash fell at Scotch Cap, forcing evacuation of its personnel and damaging Scotch Cap Light. Meltwater caused stream flooding and washed out the coast road. A Reeve Aleutian Airways pilot observed a new cinder cone, about 100 m in diameter, located near the site of Westdahl's last eruption (March-April, 1964). No lava flow has been observed. Activity declined to steaming after 9 February.

Figure 1. Enlargement of a portion of a NOAA 5 infrared image at 1835 on 8 February 1978 (0.9-km ground resolution), showing plumes, each about 60 km long, extending SE from both Westdahl and Shishaldin. Most of the Alaska Peninsula is visible, as is the coast of Alaska NW to the entrance to Kuskokwim Bay. The gray area off the coast is pack ice. Courtesy of Jürgen Kienle and NOAA.
Figure 2. Oblique airphoto taken 6 February 1978 by George Wooliver (Reeve Aleutian Airways), showing Westdahl's eruption column emerging from the cloud layer at about 3000 m altitude. Wind is from the N at about 130 km/hr. Wooliver estimated that the top of the eruption column was at 8-10 km altitude. Courtesy of Thomas Miller.
Figure 3. NOAA 5 satellite imagery, 5-9 February 1978, showing Unimak Island and vicinity. North orientations (arrow) are the same for each. A: (5 February 1978, 1036, infrared) Plume extends about 230 km S, rising to an estimated 8 km; black summit hot spot. B: (6 February 1978, 1141, infrared) Plume extends about 110 km SE; black summit hot spot. C: (7 February 1978, 1101, infrared) Plume at least 6 km high and about 160 km long, blown primarily SSE but some eastward shearing evident, probably by lower altitude winds. D: (8 February 1978, 1018, infrared) Plume extends 80 km SSE, at lower altitude than in C. E: (8 February 1978, 1018, visible, enlarged about 50% more than A-D) Weak plume curves SW to W about 100 km. Shishaldin is no longer active, 16 hours after its plume was visible in figure 11-2. The dark triangular area S of Westdahl is fresh ashfall, subtending an angle of about 95° and covering an area of about 300 km2. No ashfall is visible on Shishaldin. Courtesy of Jürgen Kienle and NOAA.

Information Contacts: J. Kienle, Univ. of Alaska; T. Miller, USGS, Anchorage.

05/1978 (SEAN 03:05) February ashfall on vessel 1,000 km SE of Westdahl

Snow contaminated by dark ash fell on the freight vessel United Spirit between 1200 and about midnight on 7 February, as it steamed from 48.8°N, 152.5°W to 49.2°N, 156.3°W, about 1,000 km SE of Westdahl. Satellite imagery (figure 3) shows that winds were driving the eruption cloud towards the vessel, about 24 hours before the ashfall began. Winds observed from the United Spirit during the snowfall were steadily from the NW.

Information Contacts: JMA, Tokyo.

09/1978 (SEAN 03:09) February eruption site visited; new crater 1.5 km in diameter and 0.5 km deep

On 6-7 August a team of six, including volcanologists Maurice and Katia Krafft and Alain Gerente, climbed Westdahl. The new crater formed by the February eruption is about 1.5 km in diameter and 0.5 km deep, at about 1450 m elevation (figure 4). Its upper portion cut through glacial ice, which reached 200 m thickness on the N rim. The bottom of the vertical-walled crater is filled with blocks, ash, ice, and talus.

Figure 4. Sketch map with cross section of Westdahl's February eruption crater and vicinity, prepared by Maurice Krafft from observations made during a visit 6-7 August 1978.

A lahar deposit, originating on the WSW flank of the new crater, extended down the glacier on Westdahl's flank to the sea, cutting the road from Cape Sarichef to Scotch Cap. The thickness of the upper portion of the deposit averaged about 50 cm, increasing to 1-3 m near the lower end.

A diary from Richard Clark (who was at Scotch Cap during the eruption) has established that the eruption began about 1330 on 4 February with the ejection of a steam cloud. Ash emission began soon afterward and ashfall started at Scotch Cap (15 km SW of the crater) at about 1600. A thunderstorm associated with the activity dropped hailstones formed around particles of ash and small lapilli. Tephra fall and the associated thunderstorm continued at Scotch Cap until mid-afternoon on 5 February. Clark reported that ash emission was continuing when he left the area during the morning of 8 February. A plume was visible in a satellite image at 1129 on 9 February (3:2). After the 9th, activity declined to steaming.

Information Contacts: M. Krafft, Cernay; R. Clark, Blaine WA.

02/1979 (SEAN 04:02) 8-km cloud seen on satellite imagery

A cloud apparently erupted from Westdahl was present on NOAA weather satellite imagery for more than 30 hours on 8 and 9 February. The cloud was first observed on an infrared image at 0352 on 8 February, about 17 hours after the previous image, on which no eruption cloud could be seen. A cloud was present on successive images on the 8th at 0926 (visible and infrared) and on the 9th at 0842 and 1037 (infrared) but not at 1958 on the 9th or 0952 on the l0th. The cloud was no more than 50 km in longest dimension on any of the images, nor was it elongated into a typical volcanic plume.

The height of the cloud was calcuated separately from infrared and visual images taken at 0926 on 8 February. Analysis of the infrared image gives a temperature of -53°C at the top of the cloud, corresponding to an altitude of slightly more than 8 km. On the visual image, measurements of the shadow cast on the weather cloud deck by the volcanic cloud result in an estimated altitude of 7.7 ± 1 km.

No activity was reported from the USCG LORAN Station at Cape Sarichef, less than 25 km from Westdahl, nor was there any aircraft confirmation of the activity.

Information Contacts: F. Parmenter, NOAA/NESS, Anchorage; J. Kienle, Univ. of Alaska; USCG LORAN Station, Unimak Island.

11/1991 (BGVN 16:11) Lava flows and tephra from 8-km NE-flank fissure

Westdahl erupted at approximately 1700 on 29 November, sending a plume of steam and ash to more than 6 km altitude. The FAA immediately rerouted air traffic to the Pacific side of the eastern Aleutians to avoid encounters with the plume, which drifted NNE over the Bering Sea.

Video and still photographs from 30 November (courtesy of the U.S. Coast Guard, Peninsula Airways, and several civilians) show that the eruption occurred from a fissure, ~8 km long, extending down the NE flank from Westdahl Peak to an elevation of ~760 m. Several large craters and gaping sinuous cracks, parallel to the fissure, formed in snow and ice fields, probably by collapse due to melting. Ash venting occurred discontinuously along most of the fissure's length, but lava fountaining was concentrated along the lower few kilometers. Several streams of fluid lava traveled E down at least two steep-walled drainages. By the second day of the eruption, the principal lava flow had moved a distance of about 4 km. Based on observations by AVO staff from a Coast Guard C-130 aircraft on 3 December, the very active flow front was 1.5 km wide, 5-10 m high, and ~7 km from the vent [figure 5]. The lava flow consisted of blocky gray aa, and widened as it reached the broad valley draining to the Pacific Ocean. As of 3 December, the front was about 10 km from the ocean. Also observed on the overflight was a dark-colored debris-flow deposit that extended to the Pacific. Streams draining the NE flank were muddy and steaming slightly when observed on 30 November and 3 December. Lava fountaining was visible, during clear weather, through 10 December, and lava flows remained active on the NE flank.

Figure 5. Sketch map of the SW part of Unimak Island, showing the eruption vents and lava flow from the Westdahl eruption as of 3 December 1991. Contour interval, 1,000 feet (about 300 m). Printed by permission of the Alaska Volcano Observatory. [Originally in 17:01]

Satellite imagery and pilot observations through mid-December indicated that the steam plume, periodically containing small quantities of ash, rose to as much as 7 km altitude and was preferentially carried NE. On 30 November, residents of False Pass, 90 km NE, reported ash-laden skies, fine ash deposition, and a strong sulfur smell that lasted into the night. Similar strong sulfur odors were reported by pilots up to several hundred kilometers inland. Light ashfall occurred again at False Pass on 9 and 12 December, and distant roaring and rumbling were occasionally heard at night through mid-December. No ash was reported in Cold Bay (145 km NE).

[No seismometers are installed on Westdahl, so information about seismicity associated with the eruption is limited. Data from the nearest seismic station, 170 km ENE of Westdahl (at Dutton), included six earthquakes of M 2.8-3.1 between 1100 and 1940 on 29 November. S-P values were consistent with epicenters in the Westdahl area, as were those recorded at Sand Point, 275 km ENE. The Dutton station also detected a tremor-like signal, different from typical noise at the site, between 1500 and 1949 on 29 November. (Originally in 17:01).]

Further Reference. Swanson, S., 1990, Westdahl, in Wood, C. and Kienle, J., Volcanoes of North America: Cambridge University Press, p. 45-46.

Information Contacts: AVO; SAB; AP.

12/1991 (BGVN 16:12) Tephra emission declines

The eruption ... continued until 15 January when a significant decrease in activity was noted. Bad weather prevented further observations of the lava flow. Aircraft pilots reported steam and ash plumes to 3.7-7.0 km altitude on 16-20 December, and 4.9 km altitude on 21-23 December. Light ashfall was noted on 16, 25, and 26 December at False Pass, 90 km NE. Residents of False Pass reported hearing rumbling for several nights prior to 30 December. Analyses of ash samples (collected 9 and 25 December) indicated a basaltic andesite composition, with [54.7]% SiO2.

Steam clouds rose to 4.6-4.9 km altitude on 2 and 3 January. Ash clouds were again observed on 8 and 9 January, rising to 2.1-2.4 km altitude. Satellite images during the late afternoon on the 9th showed the plume extending about 150 km SE. A dark spot appeared in satellite images of the volcano for several days prior to 13 January, indicating high temperatures. A black ash cloud was reported to 4 km on 13 January.

The eruption was greatly diminished in intensity on 15 January. Observers noted a small amount of steam at ground level in the vicinity of the eruption site, but there was no sign of a vertical plume. That day, an elongate area of slightly elevated temperature on the volcano's NE flank was visible in a satellite image.

[A 23 January overflight provided the first clear view of the lava flow since 3 December. The flow appeared to have widened to cover 2-3 times its 3 December area, but its front had not advanced significantly.]

Information Contacts: AVO.

01/1992 (BGVN 17:01) Eruption apparently ends; seismic data from eruption onset

Westdahl's eruption appears to have stopped. Poor weather limited observations and the stop date is uncertain, but a significant decrease in eruption intensity was noted on 15 January. Geologists noted that comparison with the 1978 eruption suggested that this cessation in activity may be only a pause.

No plume penetrated the cloud deck that obscured the summit-area fissure during a 23 January overflight. The lava flow appears to have widened to cover 2-3 times its 3 December area (figure 5), while its front had not advanced significantly. As of late January, infrared images from the NOAA-11 polar orbiting weather satellite indicated a "warm" spot in the vicinity of the volcano. Exact registration of the warm area has been difficult, but it is believed to be associated with the position of the cooling lava flow. The FAA removed all flight restrictions around the volcano on 7 February. During aerial observations by FWS personnel on 13 February, only scattered steaming was noted from the flow. Minor steaming occurred from a small cinder cone near a steep, ice-walled canyon, where the fissure vent cuts the E part of the summit glacier.

Information Contacts: AVO.

Westdahl is a broad, 1654-m-high glacier-covered volcano occupying the SW end of Unimak Island. Two peaks protrude from the summit plateau, and a new crater formed in 1978 cuts the summit icecap. The broad volcano has a somewhat of a shield-like morphology and forms one of the largest volcanoes of the Aleutian Islands. The sharp-topped, conical Pogromni stratovolcano lies 5 km north of Westdahl. Pogromni rises to 2002 m, several hundred meters higher than Westdahl, but is moderately glacially dissected and presumably older. Many satellitic cones of postglacial age are located along a NW-SE line cutting across the summit of Westdahl. Some of the historical eruptions attributed to the eroded Pogromni volcano may have originated instead from Westdahl (Miller et al. 1998). The first historical eruption of Westdahl occurred in 1795. An 8-km-long fissure extending east from the summit of Westdahl produced explosive eruptions and lava flows in 1991.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
1991 Nov 29 1992 Jan 14 Confirmed 3 Historical Observations ENE flank (1560-760 m)
[ 1979 Feb 8 ] [ 1979 Feb 9 ] Uncertain 3  
1978 Feb 4 1978 Feb 9 Confirmed 3 Historical Observations South of Westdahl Peak (1450 m)
1964 Mar 10 1964 Apr 16 Confirmed 2 Historical Observations
1827 1830 Confirmed 2 Historical Observations Pogromni or (more likely) Westdahl
1820 Unknown Confirmed 2 Historical Observations Pogromni or (more likely) Westdahl
1796 Unknown Confirmed 0 Historical Observations Pogromni or (more likely) Westdahl
1795 Unknown Confirmed 4 Historical Observations Pogromni or (more likely) Westdahl

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.


Cones

Feature Name Feature Type Elevation Latitude Longitude
Faris Peak Cone 1654 m 54° 32' 0" N 164° 11' 0" W
Pogromni
    Nosowskoj
    Kugidach-Jagutscha
    Pogrumni
    Pogrumnoy
    Devastation Volcano
Stratovolcano 2002 m 54° 34' 0" N 164° 11' 0" W
Pogromni's Sister Stratovolcano 1230 m
The summit area of Westdahl volcano, located on the southwestern part of Unimak Island in the eastern Aleutians, is seen here from the east. Westdahl Peak (left) and Faris Peak (right) cap the broad Westdahl stratovolcano. The cinder cone at the middle right marks the principal eruption site for the 1991-92 activity. Note the snow-mantled lava flow emanating from the cinder cone. The sinuous fissure cutting across the glacial icecap from the summit formed in the opening phases of the eruption and was the location of spectacular lava fountaining.

Photo by C.F. Zeillemaker, 1993 (U.S. Fish and Wildlife Service, courtesy of Alaska Volcano Observatory).
This 1992 oblique view up the eastern flank of Westdahl volcano was taken 2 months after the end of a major east-flank eruption. The dark, blocky lava flows are from the 1991-92 eruption; note wisps of steam scattered across the lava flow surface. The eruption took place from an 8-km-long fissure that extended from the summit down the east flank. It began on November 29, 1991, with a 6-km-high eruption plume. The lava flow traveled as far as 7 km from the principal vent, widening as it reached the lower flanks.

Photo by C. Dau, 1992 (U.S. Fish and Wildlife Service, courtesy of Alaska Volcano Observatory).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Coats R R, 1950. Volcanic activity in the Aleutian Arc. U S Geol Surv Bull, 974-B: 35-47.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Lamb H H, 1970. Volcanic dust in the atmosphere; with a chronology and assessment of its meteorological significance. Phil Trans Roy Soc London, Ser A, 266: 425-533.

Miller T P, McGimsey R G, Richter D H, Riehle J R, Nye C J, Yount M E, Dumoulin J A, 1998. Catalogue of the historically active volcanoes of Alaska. U S Geol Surv Open-File Rpt, 98-582: 1-104.

Motyka R J, Liss S A, Nye C J, Moorman M A, 1993. Geothermal resources of the Aleutian arc. Alaska Div Geol Geophys Surv, Prof Rpt, no 114, 17 p and 4 map sheets.

Myers J D, 1994. The Geology, Geochemistry and Petrology of the recent Magmatic Phase of the Central and Western Aleutian Arc. Unpublished manuscript, unpaginated.

Smith R L, Shaw H R, Luedke R G, Russell S L, 1978. Comprehensive tables giving physical data and thermal energy estimates for young igneous systems of the United States. U S Geol Surv Open-File Rpt, 78-925: 1-25.

Wood C A, Kienle J (eds), 1990. Volcanoes of North America. Cambridge, England: Cambridge Univ Press, 354 p.

Volcano Types

Stratovolcano?
Pyroclastic cone(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Basalt / Picro-Basalt
Trachyandesite / Basaltic trachy-andesite
Andesite / Basaltic Andesite
Minor
Trachyte / Trachyandesite
Dacite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
0
0
0
305

Affiliated Databases

Large Eruptions of Westdahl Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.