May 15, 2003
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
First Historical Eruption of Anatahan Volcano, Northern Mariana Islands
For the past week, a billowing column of dark volcanic ash has been erupting from Anatahan Volcano in the Northern Mariana Islands, burying parts of the volcano with more than 45 cm (18 inches) of ash and sending a dilute eruption cloud more than 1000 km (600 miles) to the west. This is the first eruption from the volcano in historical time, but it didn't come as much of a surprise to people familiar with Anatahan, especially to scientists of the Hawaiian Volcano Observatory (HVO) who worked there in 2001 with personnel from the Emergency Management Office (EMO) of the Commonwealth of the Northern Mariana Islands.
Anatahan Volcano is a small volcanic island located 320 km (200 miles) north of Guam. The island is about 9 km (5.6 miles) long and 3 km (2 miles) wide. Anatahan is a stratovolcano that consists of the largest known caldera in the Northern Mariana Islands. In 1990, when geologists from HVO, EMO, and the University of Hawai`i examined the rock layers of Anatahan, they discovered abundant evidence of ancient explosive eruptions that sent fast-moving flows of hot ash and rocks across the island.
The eruption began suddenly on the evening of May 10. No one was directly threatened by the initial activity-residents had long before evacuated the volcano, but not because of recent warnings from the volcano or officials from EMO. Most residents were evacuated in 1990 after a shallow earthquake swarm hinted at the possibility of volcanic activity; another swarm of earthquakes occurred in 1993. Any remaining residents on the island were likely driven away by destructive typhoons of the past year.
Within hours of the eruption's onset, a towering column of volcanic ash and gas rose to more than 10 km (33,000 feet) above sea level, and the prevailing wind blew the ash westward. An immediate concern that was felt far beyond the Western Pacific was the potential for the tiny abrasive ash fragments to damage aircraft passing nearby and downwind from the volcano.
Commercial flights between Hawai`i and the Philippines and Hong Kong, and between Japan, Saipan, Guam, Australia, and New Zealand, pass over volcanoes of the Northern Mariana Islands. When an explosive eruption from these islands sends volcanic ash and gas high enough to affect aircraft, it is extremely important for pilots already in the air, and airline dispatchers on the ground, to receive immediate notification of the activity and location of the resulting eruption cloud.
Engines of jet aircraft have failed within minutes of encountering a thick cloud of volcanic ash particles, and many aircraft surfaces and internal electronics can suffer severe damage from ash. More than 80 commercial aircraft have unexpectedly encountered volcanic ash in flight and at airports in the past 20 years.
The job of tracking eruption clouds from the Northern Mariana Islands is the responsibility of the Washington Volcanic Ash Advisory Center (VAAC) in Camp Springs, Maryland. The Washington VAAC issued a series of Volcanic Ash Advisories that identified the estimated location of the eruption cloud based on satellite images and pilot reports. The advisories are distributed through several global networks and served on the Internet.
The Washington VAAC also issued forecasts of where the eruption cloud was likely to go, based on predicted winds. These forecasts, called a Volcanic Ash Forecast Transport and Dispersion model, estimate the location of the eruption cloud at different elevations above sea level for 12-hour time intervals after the eruption began.
No one knows how this eruption may proceed in the next few weeks to months. Very little is known about Anatahan's eruptive history, and the volcano is not currently monitored with real-time volcano sensors that scientists need in order to track the intensity of an ongoing eruption.
In the 1980s and 1990s, HVO scientists assisted the EMO in installing one or two seismometers on several of the volcanoes of the Northern Mariana Islands, including Anatahan, but the single station on the volcano was not operating before the eruption. As scientists have learned elsewhere, a robust volcano-monitoring program is necessary to evaluate the potential for stronger volcanic activity in the near future.
Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued unabated during the past week. Streams of lava are still visible on Pulama pali and Paliuli. The lava breaks out of the main Mother's Day tube above Pulama pali and wends it way to the coastal flat in a series of open channels and tubes. Surface flows are found near the base of Paliuli, and the National Park Service has marked a trail out to the closest activity. Ocean entry activity at the West Highcastle delta was weak and intermittent during the week. Another active lobe of the Mother's Day flow is approaching the ocean and is within 150 meters (500 ft) of the coast at Highcastle.
The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The steam clouds are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary and onto the lava deltas and benches.
No earthquakes were reported felt during the past week.
Updated: May 19, 2003 (pnf)