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  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 39.95°N
  • 139.73°E

  • 291 m
    954 ft

  • 283262
  • Latitude
  • Longitude

  • Summit

  • Volcano

The Global Volcanism Program has no activity reports for Megata.

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

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

Geological Background

Megata, a group of three small maars along the tip of the Oga Peninsula in NW Honshu, has been active during the Holocene (Ishikawa et al., 1957). Lakes 300-600 m wide fill the basaltic-to-dacitic maars, which are a noted locality for mantle-derived xenoliths. Ichinomegata, the easternmost, largest, and oldest of the three maars, is 600 m in diameter. Ninomegata and Sannomegata are located immediately east and south of Toga Bay (Togowan), which itself is a maar. The rim of the rhyolitic Toga (Togowan) maar, larger than the Megata maars, is breached by the sea on the western side and was formed about 450,000 years ago. The Megata maars are mostly late Pleistocene in age, but Murayama (1987) noted that pottery from roughly 4000 years before present (Jomon Period) has been found within tephra layers from the maars.

Eruptive History

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

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2050 BCE (?) Unknown Confirmed   Tephrochronology
7050 BCE (?) Unknown Confirmed   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.


Feature Name Feature Type Elevation Latitude Longitude
Maar 161 m 39° 57' 0" N 139° 45' 0" E
Ninomegata Maar 199 m 39° 57' 0" N 139° 44' 0" E
Sannomegata Maar 291 m 39° 56' 0" N 139° 43' 0" E
Maar 39° 57' 2" N 139° 43' 4" E

Photo Gallery

An aerial view from the NW with Toga Bay in the foreground shows Sannomegata (center), one of a group of the three small Megata maars along the tip of the Oga Peninsula. The names of the three maars, Ichinomegata, Ninomegata, and Sannomegata mean First, Second, and Third Megata, respectively. Lakes 300-700 m wide fill the maars, which are noted localities for mantle-derived xenoliths and are located immediately east and south of Toga Bay.

Copyrighted photo by Hiroshi Yagi (Japanese Quaternary Volcanoes database, RIODB, and Geol Surv Japan, AIST,


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.

Hasenaka T, Ui T, Nakamura Y, Hayashi S, 1992. Traverse of Quaternary volcanoes in Japan. 29th Internatl Geol Cong, Kyoto, Field Trip A06, 74 p.

Hayakawa Y, 1994. A catalog of the volcanic eruptions during the last 2000 years in Japan. Sci Rpt Fac Education Gumma Univ, (in Japanese with English abs).

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

Ishikawa T, Minato M, Kuno H, Matsumoto T, Yagi K, 1957. Welded tuffs and deposits of pumice flow and nuee ardente in Japan. 20th Internatl Geol Cong, Mexico City, Sec 1: 137-150.

Koyaguchi T, 1986. Life-time of a stratified magma chamber recorded in ultramafic xenoliths from Ichinomegata volcano, northeastern Japan. Bull Volc, 48: 313-323.

Nakano S, Yamamoto T, Iwaya T, Itoh J, Takada A, 2001-. Quaternary Volcanoes of Japan. Geol Surv Japan, AIST,

Ono K, Soya T, Mimura K, 1981. Volcanoes of Japan. Geol Surv Japan Map Ser, no 11, 2nd edition, 1:2,000,000.

Takahashi E, 1978. Petrologic model of the crust and upper mantle of the Japanese island arcs. Bull Volc, 41: 529-547.

Volcano Types


Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Andesite / Basaltic Andesite
Basalt / Picro-Basalt


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

Affiliated Databases

Large Eruptions of Megata 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.