Another small eruption at Asamayama volcano, Japan

Another small eruption at Asamayama volcano, Japan

Another small eruption took place at Japan's Asamayama volcano at 10:28 UTC (19:28 LT) on August 25, 2019. The alert level remains unchanged at 2 of 5. The volcano is located about 140 km (87 miles) NW of capital Tokyo. This volcano has had several major plinian eruptions, the last two of which occurred in 1108 (VEI 5) and 1783 (VEI 4). 

The eruption on August 25 ejected volcanic ash about 600 m (1 968 feet) above the crater, the Japan Meteorological Agency (JMA) said. This is 3 168 m (10 393 feet) above sea level.

JMA warned of possible airborne rock debris and pyroclastic flows within about a 2 km (1.2 miles) radius of the crater.

The eruption follows another similar eruption at 13:08 UTC on August 7, 2019, when the alert level was raised from 1 to 3.

JMA said at the time it expects more eruptions, capable of affecting nearby communities. Pyroclastic flows are possible within 4 km (2.5 miles) of the crater, it said, urging residents and tourists not to approach the volcano.

On August 7, volcanic ash rose up to 4 300 m (14 100 feet) above sea level, about 1 800 m (5 900 feet) above the crater. Local authorities said there were no immediate reports of injuries.

Both seismic activity and sulfur dioxide emissions temporarily increased and then decreased later that day. During August 8 - 19, white plumes generally rose 400 m (1 312 feet) above the crater rim; occasionally they rose as high as 800 m (2 624 feet). Sulfur dioxide emissions were 70 - 300 tons per day.

On August 19, the Alert Level was lowered to 2 (on a scale of 1-5).

Asamayama eruption on August 7, 2019. Image credit: JMA

JMA said that activity at the volcano had been progressively increasing during the first half of June 2019. From June 2 - 5, a plume rose less than 400 m (1 300 feet) above the active crater. Weak incandescence from the summit crater was recorded at night with a webcam. Sulfur dioxide flux was a little higher than 900 tons per day when measured on June 2.

Plumes were rising as high as 300 m (984 feet) above Asamayama’s summit crater from June 16 - 23, JMA said, adding that weak crater incandescence was visible for the first time since December 23, 2017.

Geologic summary

Asamayama, Honshu's most active volcano, overlooks the resort town of Karuizawa, 140 km (87 miles) NW of Tokyo. The volcano is located at the junction of the Izu-Marianas and NE Japan volcanic arcs. The modern Maekake cone forms the summit and is situated east of the horseshoe-shaped remnant of an older andesitic volcano, Kurofuyama, which was destroyed by a late-Pleistocene landslide about 20 000 years before present (BP).

Growth of a dacitic shield volcano was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14 000 - 11 000 BP, and by growth of the Ko-Asama-yama lava dome on the east flank. Maekake, capped by the Kamayama pyroclastic cone that forms the present summit, is probably only a few thousand years old and has an historical record dating back at least to the 11th century CE.

Maekake has had several major plinian eruptions, the last two of which occurred in 1108 (Asamayama's largest Holocene eruption) and 1783 CE. (GVP)

Featured image credit: Richard Fiske, Smithsonian Institution

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