Ukinrek Maars

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  • United States
  • Alaska
  • Maar(s)
  • 1977 CE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 57.832°N
  • 156.51°W

  • 91 m
    298 ft

  • 312131
  • Latitude
  • Longitude

  • Summit

  • Volcano

The Global Volcanism Program has no activity reports for Ukinrek Maars.

The Global Volcanism Program has no Weekly Reports available for Ukinrek Maars.

Index of Monthly 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.

03/1977 (SEAN 02:03) Explosions send ash plume above 6 km height

04/1977 (SEAN 02:04) Two new maars formed NW of Peulik volcano after 30 March

05/1977 (SEAN 02:05) Periodic earthquake swarms near the new vents

04/1998 (BGVN 23:04) Tectonic earthquake swarm in the Ukinrek Maars area

05/1998 (BGVN 23:05) Earthquake swarm decreases in rate and intensity

Contents of Monthly Reports

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

All times are local (= UTC - 8 hours)

03/1977 (SEAN 02:03) Explosions send ash plume above 6 km height

On 30 March, explosions were reported at 1500 and 1720 from a vent 13 km [but see 2:4] NW of Peulik volcano. The latter explosion was viewed from close range from a Wien Air Alaska plane. Its crew reported that the dense, ash-laden eruption cloud rose higher than 6,000 m. Peulik, an 1,844-m stratovolcano with a dacite lava dome, last erupted in 1852. It is surrounded by several small olivine andesite scoria cones.

Information Contact: T. Miller, USGS, Anchorage.

04/1977 (SEAN 02:04) Two new maars formed NW of Peulik volcano after 30 March

Two new maars formed in tundra terrain, 15 km NW of Peulik volcano, between 30 March and 9 April. Explosions were first observed on 30 March from 70 km SW of the eruption site. Pilots who overflew the eruption at 1725 and 1800 reported a single vent, 20-30 m in diameter, that emitted white steam, then a dark, ash-laden cloud that rose 6,000-7,500 m. Fine ash fell 135 km ESE of the vent, and a sulfurous haze layer lay over Kodiak (250 km E of the vent) all day. More ash clouds were seen on 1 and 2 April.

On 2 April, the original crater had filled with water and become quiescent, and a new 60-m-diameter vent had formed 500 m to the E. By the early afternoon of 3 April, the E crater had grown to about 100 m in diameter and contained a yellowish-orange lava lake. Fragments up to 1 m across were being ejected to 300 m height. Later in the afternoon, 15-20-m lava fountains were observed.

An ash cloud rising more than 4,000 m deposited traces of ash 95 km to the N on 5 April, but by 6 April activity had declined to steam emission and some ash explosions, which sent tephra to more than 1,000 m above the lava lake. Similar activity, including 30-m orange-red lava fountains, was reported on 7 April. No further eruptions were reported until the early morning of 9 April, when violent explosions of incandescent material were seen 30 km away.

A team of volcanologists from the University of Alaska and Dartmouth College visited the eruption site 14-21 April. The W crater was oblong (150 x 65 m) and filled with lukewarm, slightly acidic water. The E crater was about 250 m in diameter and 100 m deep. About 2/3 of its floor was occupied by a lava dome up to 40 m high that was degassing and was coated with sulfur and hematite. Ground water emerged from the crater walls at 50-70 m depth and cascaded onto the dome, where it flashed to steam. Occasional ash puffs were created by the caving of the steep crater walls. Blocks and boulders of highly variable composition and various degrees of rounding, and olivine basalt bombs with lithic cores, decreased in size from 1.5 m in diameter near the crater rims to about 50 cm diameter a few hundred meters away. Fist-sized cinders fell as far as 2 km away. Stripped bark, and mud with imbedded scoria plastered against tree trunks 500 m from the vents, indicate at least minor base surge activity during 1 or more explosions of the E crater.

Two portable short-period seismograph systems, which operated from 15-20 April, recorded a high level of microearthquake activity and three distinct earthquake swarms of several hours duration. More than 1 event per minute was recorded during the swarms. Many of the smaller events were shallow, but some of the larger ones showed S-P times indicating hypocenter depths between a few km and 20 km. Some of the larger events were also recorded by a permanent University of Alaska seismic station 25 km N of the eruption site.

Information Contact: J. Kienle, Univ. of Alaska.

05/1977 (SEAN 02:05) Periodic earthquake swarms near the new vents

When visited in late May, the E vent was filling with water. A glow could be seen through fractures in the E vent dome, which had ceased growing and was degassing less vigorously than in mid-April. The vents are located on the Bruin Bay Fault. Its projected trend cuts an area of about 12 new hot springs that have formed about 3 km to the N in Becharof Lake. Periodic earthquake swarms continued to occur in the vicinity of the new vents. A third seismograph station was added in late May to the two installed in April.

Further References. Kienle, J., Kyle, P.R., Self, S., Motyka, R.J., and Lorenz, V., 1980, Ukinrek Maars, Alaska, I. April 1977 eruption sequence, petrology and tectonic setting: JVGR, v. 7, p. 11-38.

Kienle, J., and Swanson, S.E., 1983, Volcanism in the eastern Aleutian Arc: late Quaternary and Holocene centers, tectonic setting, and petrology: JVGR, v. 17, p. 393-432. (This reference also contains data on Augustine and Iliamna.)

Self, S., Kienle, J., and Huot, J.P., 1980, Ukinrek Maars, Alaska, II. Deposits and formation of the 1977 craters: JVGR, v. 17, p. 39-66.

Information Contact: J. Kienle, Univ. of Alaska.

04/1998 (BGVN 23:04) Tectonic earthquake swarm in the Ukinrek Maars area

During 8-9 May, a seismic swarm of tectonic earthquakes shook the middle Alaskan Peninsula region including the towns of King Salmon, Dillingham, Egegik, and Pilot Point. The swarm began with five earthquakes of M 5.2-4.7 occurring between 1630 and 2259. Dozens of earthquakes in the M 2.5-3.5 range were felt locally. The earthquakes continued through 9 May, but the number of earthquakes had decreased notably by the morning of 10 May. Felt earthquakes were still occurring at a rate of 1-2/day as of the afternoon of 12 May.

The earthquakes were clustered on the SW shore of Lake Becharof, approximately 10-20 km NW of the 1977 Ukinrek Maars volcanoes and near the S end of the Bruin Bay fault. The earthquakes were all very shallow (<7 km in depth). In the past, the few local seismic stations have been able to accurately locate earthquakes only of magnitudes greater than M 4. The recent expansion of Alaska Volcano Observatory (AVO) volcano seismic monitoring to include volcanoes in Katmai National Park, NE of Lake Becharof, and Aniakchak Volcano, to the SW, has allowed better detection and location of Becharof earthquakes.

AVO scientists traveled to King Salmon on 9 May for an overflight of the swarm location and vicinity. Their U.S. Fish and Wildlife Service (FWS) pilot had overflown the area the evening of 8 May after the first earthquakes. Nothing indicating any volcanic activity or surface breakage was seen on either flight. Some small slumping was noticed along the SW shoreline of Lake Becharof and some local discoloration by sediments was seen both likely resulting from ground shaking. Similarly, a slight change in the green coloration of the crater lake in the large maar at Ukinrek Maars was likely due to disturbed sediments. No evidence of any disturbance or unusual activity was seen at Peulik volcano. Peulik is heavily snow-covered and showed no sign of discoloration, deformation, or slumping. The area of seismicity is not monitored by real-time seismic instrumentation; scientists scouted for possible locations to establish a temporary seismic net. The net will allow scientists to determine if there is a volcanic component to the earthquake swarm and any potential volcanic hazard. AVO is also in communication with citizens of King Salmon, Egegik, Meshik, and Pilot Point, as well as the National Park Service and FWS pilots who frequently overfly the area.

The preliminary interpretation is that the swarm was of tectonic origin, although the occurrence of five M 4.7-5.2 earthquakes in such a short time with no clear mainshock may suggest a volcanic component. Considering the nature of the formation of Ukinrek Maars in 1977, where no volcano existed previously, intrusion of magma associated with tectonic movement is possible. There is no evidence of imminent volcanic hazard from this seismic swarm.

Background. The May 1998 swarm was the most energetic to date. There were no major seismic events detected in association with the 1977 Ukinrek Maars eruptions, except for a number of small events detected by a portable seismic net which was deployed by the University of Alaska at Fairbanks (UAF) and the U.S. Geological Survey (USGS) for several months following the 1977 eruptions. Ukinrek Maars formed 30 March-10 April, 1977 as a result of magmatic intrusion into water-saturated glacial till 2 km S of Gas Rocks on the S shore of Lake Becharof. During a 10-day period, violent explosions produced steam and ash plumes as high as 6.5 km and light ash fall as far as 160 km to the N. Since the Ukinrek Maars formed, CO2 gas has been continuously emitted from the vicinity of the maars, the Gas Rocks, and from beneath Lake Becharof.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL:, b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Roger Hansen, Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775 USA (Email:

05/1998 (BGVN 23:05) Earthquake swarm decreases in rate and intensity

During the last week of May, the anomalous seismic activity under SW Lake Becharof (BGVN 23:04) continued but at a decreased rate and intensity; magnitudes of 12 located earthquakes ranged from M 1.7 to 3.3. During 1-5 June, 20 earthquakes were located ranging from M 1.8 to 4.3. Activity decreased significantly during 6-12 June; only four earthquakes were located, all M > 3.0. Several overflights of the location by AVO scientists revealed no signs of volcanic activity or surface breakage. The area of seismicity was not monitored by real-time seismic instrumentation; however, a portable seismic instrument has recently been installed. AVO is in communication with local citizens and land managers who frequently overfly the area. There was no evidence of imminent hazard at the site.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL:, b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Ukinrek Maars are two explosion craters that were created in an area without previous volcanic activity during a 10-day-long phreatomagmatic eruption March-April 1977. The basaltic maars were erupted through glacial deposits in the Bering Sea lowlands 1.5 km south of Becharof Lake and 12 km west of Peulik volcano; their location is related to the regional Bruin Bay fault. The elliptical West Maar, which was the first to form, is 105 x 170 m wide and 35 m deep. The other maar, 600 m to the east, is 300 m wide and 70 m deep. Both maars are now filled by crater lakes; the eastern lake encircles a 49-m-high lava dome that was emplaced at the end of the eruption. Base surges were directed primarily to the NW. Juvenile material from the Ukinrek eruptions was of mantle-derived olivine basaltic composition. The dacitic Gas Rocks lava domes, of Quaternary age, are located on the shores of Becharof Lake, 3 km north of Ukinrek maars and were the site of a phreatic eruption about 2300 years ago.

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

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
1977 Mar 30 1977 Apr 9 Confirmed 3 Historical Observations West and East Ukinrek Maars
0350 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected) Gas Rocks

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.

Feature Name Feature Type Elevation Latitude Longitude
East Maar Maar
West Maar Maar

Feature Name Feature Type Elevation Latitude Longitude
Gas Rocks, The Dome
Vigorous phreatomagmatic eruptions produced when magma came in contact with groundwater eject an ash-rich column at the Ukinrek Maars on the Alaska Peninsula. This photo from the south on April 5, 1977, shows explosive eruptions from East Maar, one of two new craters that were blasted through glacial sediments in an area without previous volcanic activity. The hummocky, snow-covered surface in the foreground is that of a debris-avalanche deposit from Peulik volcano.

Photo by Jim Faro (Alaska Department of Fish and Game).
An aerial view into East Maar on April 3, 1977, shows incandescent lava on the floor of the crater and a small phreatomagmatic vent above it that is producing an ash column. The 1977 eruptions of Ukinrek Maars began on March 30 at West Maar, which was formed during the first 3 days of the eruption. East Maar formed during the next 7 days at a location 600 m to the east. A lava dome, now covered by a crater lake, was erupted on the floor of East Maar.

Photo by Ken Parker, 1977 (Alaska Department of Fish and Game).
Ukinrek Maars are two explosion craters that were created in an area without previous volcanic activity during a phreatomagmatic eruption March-April 1977. A greenish lake fills East Maar, the largest of the Ukinrek Maars in this 1994 view from the south. East Maar and the smaller West Maar, within the dark tephra blanket near the left margin, were formed during the 10-day-long eruption that began on March 30, 1977. Gas Rocks, an older glaciated volcanic center, forms the peninsula extending into Becharof Lake in the background.

Photo by Chris Nye, 1994 (Alaska Division of Geological and Geophysical Surveys, Alaska Volcano Observatory).
An ash-rich eruption column rises above the eastern crater of the newly formed Ukinrek Maars on April 6, 1977. West Maar was formed during the initial days of the eruption, which began on March 30. Three days later explosions began at East Maar, 600 m away. At the peak of the eruption ash plumes reached up to 6 km above the vent. On the 4th day of the eruption a lava dome appeared within East Maar.

Photo by R. Russell, 1977 (Alaska Department of Fish and Game).
The interaction of magma with groundwater produced this dark, ash-rich eruption column in 1977 from the Ukinrek Maars on the Alaska Peninsula. The eruption occurred in an area without previous volcanic activity, when magma rose along a fault that cut through low-lying surficial glacial deposits. The phreatomagmatic explosions created two new craters, which were named after the Yupik Eskimo words for "two holes in the ground." This photo was taken from the WSW on April 6, 1977.

Photo by R. Russell, 1977 (Alaska Department of Fish and Game).
Explosive craters, known as maars, originate from strong explosive eruptions involving magma-water interaction. This lake-filled crater and another small crater (left) are the Ukinrek Maars, which formed during an eruption in 1977 in a lowland area of the Alaska Peninsula west of the main volcanic chain. The contact between lighter and darker material in the walls of the lake-filled eastern maar marks the original pre-eruption surface, which is now blanketed by a dark apron of ejecta produced during the eruption.

Photo by Christina Neal, 1993 (Alaska Volcano Observatory, U.S. Geological Survey).

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.

Fierstein J, 2007. Explosive eruptive record in the Katmai region, Alaska Peninsula: an overview. Bull Volc, 69: 469-509.

Hildreth W, Fierstein J, Calvert A T, 2007. Blue Mountain and the Gas Rocks: rear-arc dome clusters on the Alaska Peninsula. In: Haeussler P J, Galloway J P (eds), Studies by the U.S. Geological Survey, {U S Geol Surv Prof Pap}, 1739-A: 1-27.

Kienle J, Kyle P R, Self S, Motyka R J, Lorenz V, 1980. Ukinrek Maars, Alaska, I. April 1977 eruption sequence, petrology and tectonic setting. J Volc Geotherm Res, 7: 11-37.

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.

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

Volcano Types

Lava dome(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Basalt / Picro-Basalt


Within 5 km
Within 10 km
Within 30 km
Within 100 km

Affiliated Databases

Large Eruptions of Ukinrek Maars 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.