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Chokai Volcano | John Seach
Honshu, Japan
39.08 N, 140.03 E
summit elevation 2237 m
stratovolcanoes
Chokai volcano is located in northern Honshu, bordering the Sea of Japan. Chokai is a large stratovolcano with two peaks (Nishi-Chokai and Higashi-Chokai).
The volcano is located 60 km back arc side of the volcanic front of
the northeast
Japan arc. The height of the volcano is 2,000 m from its base, and
the diameter at the base is 20 km x 15 km elongated in a WNW
direction.
History of the Volcano
The growth of a stratovolcano in the west was followed by the
formation of an explosion crater at the summit. The main vent then
shifted 3 km east and formed a new stratovolcano. An explosive
eruption formed a caldera which opened to the north. Recent
eruptions have occurred mainly inside of the younger caldera.
1974 Eruption
The eruption at Chokai volcano was preceded by small earthquakes
beginning December 1973. In early January, a climber reported an
unusual phenomenon at the summit of the volcano, which was possibly
increased fumarolic activity. In late February 1974, inhabitants
living on the eastern foot of the volcano, 10 km from the summit,
heard sounds like gun shooting or thunder in the direction of the
volcano. The eruption was first observed by a pilot on 1st March
1974. A new crater, about 50 m in diameter formed at the eastern
base of 1801 lava dome (Shinzan). On 6th March 1974 a mud flow, 2 km
long, was observed slowly flowing on the snow-covered northern floor
of the caldera, followed by a decrease in activity.
Eruptions resumed on 24th April 1974 at Chokai volcano at Kojindake
crater. The eruption ejected material from the 1801 and 1821
eruptions which had filled the crater. The explosive eruption of the
second cycle continued intermittently
until 30th April 30. This was followed by weak fumarolic activity
from both craters until October 1974.
Production of rooster tail jets, and rapid melting snow resulting
in mud flows, indicated fresh magma reached a shallow depth during
the 1974 eruption of Chokai volcano.
1821 Eruption
Phreatic explosions were recorded in 1821 in the caldera.
1801 Eruption
An eruption in 1801 for a dome called Shinzan which covered a maar
and a spine in the caldera.
Further Reading
Hayashi, S., 1984. Geology of Chokai volcano. The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists, 79(6), pp.249-265.
Hayashi, S., 1984. Petrology of Chokai volcano. Part I Petrography and major element compositions. The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists, 79(12), pp.475-483.
Chokai Volcano Eruptions
1974, 1821, 1800-04, 1764, 1740-41, 1738, 1735, 1659-63, 1560?,
1477?, 999?, 948, 939, 915, 884, 871, 861, 857, 856, 839, 829, 817,
804-06, 717?, 711, 610?, 577-78, 573.