Anatahan Volcano - John Seach


Mariana Islands

16.35 N, 145.67 E
summit elevation 788 m

Anatahan Island is situated about 120 km north of Saipan - the capital of the Commonwealth of the Northern Mariana Islands. It lies at the southern end of the 1500-km-long Izu-Bonin- Mariana arc.

The island of Anatahan is only 1% of the volume of the entire volcano, which is 3700 m high from submarine base to summit, and an average diameter of 35 km. The highest point on the island is immediately west of the caldera.

Anatahan Island measures 9 km (east–west) by 3.7 km (north–south). The summit of the island contains an elongate caldera, 5 km by 2 km. The caldera is approximately 10 sq km in size and occupies about a third of the island’s area.

The east crater is located in the eastern part of the caldera. It is a a pit crater 1.4 km by 1.2 km in diameter, and 200 m deep.

2008 Activity
Seismic activity increased at Anatahan volcano in January 2008. A faint ash plume to 5,000 ft altitude was visible at Anatahan volcano on 28th July 2008.

2005 Eruption
The largest eruption of Anatahan volcano occurred on April 6, 2005, when ash reached 50,000 ft altitude. The eruption ejected about 50 million cubic meters of ash. A plume of vog from that eruption spread over the Philippine Sea, reaching about 1200 nautical miles west of Anatahan.

2003 Eruption
The first recorded eruption of Anatahan volcano occurred on 10th May 2003. Only sulfataric activity was observed previous to this eruption. The eruption ejected reddish brown ash to a height of 13 km. The eruption occurred from the east crater of the volcano.
A swarm of volcano-tectonic earthquakes occurred on the 10th May 2003 northeast of the island preceded the eruption. At 0500 UTC, the earthquakes surged to more
than 100 events per hour, with magnitudes less than 2. On 12th May Anatahan and
surrounding waters to a distance of 48 km were declared off limits to boats and aircraft not involved in hazard evaluations. Moderate to vigorous activity continued until 28th May 2003. Between 28th May and 5th June, an ashfall and small surge passed through the east flank crater. Dome growth occurred between 5-14 June. The small lava dome was destroyed by an eruption on 14th June.

2001 Geothermal Activity
In June 2001 there was a small increase in the area of geothermal activity around a couple of pits at the volcano.

1992-94 Seismicity
A few swarms of small, local, earthquakes occurred at Anatahan volcano between May–July 1993. Nine earthquakes larger than magnitude 4.5 occurred between late 1992 and May of 1994.

1990 Earthquakes
In March and April 1990, increased local seismicity, a large regional earthquake, and reported increased fumarolic activity in the pit crater, resulting in the evacuation of Anatahan village, at the west end of the island. A helicopter overflight noted a change in the pit crater lake from its typical green color to bluish gray, increased
fumarolic activity, a fresh landslide in the pit crater, and the odor of H2S. On 5th April 1990, a magnitude 7.5 earthquake occurred 150 km east of Anatahan, in the Mariana trench.

Anatahan Volcano Eruptions

2008, 2006, 2005, 2004, 2003