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  • United States
  • Alaska
  • Stratovolcano
  • 7600 BCE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 54.8°N
  • 163.589°W

  • 1871 m
    6137 ft

  • 311380
  • Latitude
  • Longitude

  • Summit

  • Volcano

The Global Volcanism Program has no activity reports for Roundtop.

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

The Global Volcanism Program has no Bulletin Reports available for Roundtop.

Basic Data

Volcano Number

Last Known Eruption



7600 BCE

1871 m / 6137 ft


Volcano Types

Lava dome

Rock Types


Tectonic Setting

Subduction zone
Continental crust (> 25 km)


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

Geological Summary

The flat-topped, glacier-covered Roundtop volcano is the easternmost and lowest of an E-W-trending line of volcanoes on eastern Unimak Island. Roundtop lies 13 km SW of the village of False Pass. The snow and ice-covered edifice fills much of a 3-km-wide caldera that formed during the early Holocene. The caldera-forming eruption produced pyroclastic flows and a rhyolitic tephra layer that is widespread throughout the southwestern end of the Alaska Peninsula. A group of lava domes was constructed south of Roundtop volcano. No historical eruptions are known from the 1871-m-high stratovolcano. In the 1930s warm springs were found on its slopes.


The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

Carson E C, Fournelle J H, Miller T P, Mickelson D M, 2002. Holocene tephrochonology of the Cold Bay area, southwest Alaska. Quat Sci Rev, 21: 2213-2228.

Fournelle J H, 1988. The geology and petrology of Shishaldin volcano, Unimak Island, Aleutian arc, Alaska. Unpublished PhD thesis, John Hopkins Univ, 507 p.

Henning R A, Rosenthal C H, Olds B, Reading E (eds), 1976. Alaska's volcanoes, northern link in the ring of fire. Alaska Geog, 4: 1-88.

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

Miller T P, 1999. Newly identified early Holocene caldera-forming druption from Roundtop volcano, Unimak Island, Alaska. Eos, Trans Amer Geophys Union, 1999 Fall Mtg, abs V51B-17.

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.

Smith R L, Shaw H R, 1975. Igneous-related geothermal systems. U S Geol Surv Circ, 726: 58-83.

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.

Eruptive History

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

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
7600 BCE ± 500 years Unknown Confirmed 5 Tephrochronology

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.


Khaginak (?)

Photo Gallery

Three prominent volcanoes are constructed along an E-W line on the eastern half of Unimak Island. The aptly named Roundtop volcano in the lower foreground is glacially eroded and has had no historical eruptive activity. In the 1930s warm springs were found on its slopes. The recent discovery of Holocene pyroclastic-flow deposits and a group of lava domes south of Roundtop indicate it is still an active volcano. The glacially dissected Isanotski volcano and the beautifully symmetrical Shishaldin volcano are the prominent peaks behind Roundtop.

Photo by Clayton and Marcia Brown, 1986 (courtesy of John Reeder, Alaska Div. Geology Geophysical Surveys).
Three prominent stratovolcanoes are constructed along an E-W line on Unimak Island. Steaming Shishaldin, the highest of the three, rises to 2857 m in the foreground and is one of the most active volcanoes in the Aleutians. The dissected Isanotski volcano (right) has had reported eruptions of uncertain validity, and Roundtop volcano (center distance) has had Holocene eruptions, but no historical activity.

Photo by Clayton and Marcia Brown, 1987 (courtesy of John Reeder, Alaska Div. Geology & Geophysical Surveys).
The flat-topped, glacier-covered Roundtop volcano, rising to the west beyond buildings of the village of False Pass, is the easternmost and lowest of an E-W-trending line of volcanoes on Unimak Island. Roundtop has produced Holocene pyroclastic flows, and a group of lava domes was constructed south of the volcano. No historical eruptions are known from the 1871-m-high stratovolcano. In the 1930s warm springs were found on its slopes.

Photo by Game McGimsey, 1998 (Alaska Volcano Observatory, U.S. Geological Survey).

Smithsonian Sample Collections Database

There are no samples for Roundtop in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

Affiliated Sites

Large Eruptions of Roundtop 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).
MODVOLC - HIGP MODIS Thermal Alert System Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.
MIROVA Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.