Chokai Volcano - John Seach


Honshu, Japan

39.08 N, 140.03 E
summit elevation 2237 m

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.

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.