America’s Volcanoes

The weekly update from AVO:

Friday, August 31, 2007 11:50 AM AKDT (1950 UTC)

PAVLOF VOLCANO (CAVW#1102-03-)
55°24′57″ N161°53′24″ W, Summit Elevation 8261 ft (2518 m)
Current Aviation Color Code: ORANGE
Current Volcano Alert Level: Watch

The eruption of Pavlof Volcano that began August 15th continues. Seismicity has steadily increased over the past week and is characterized by volcanic tremor, frequent explosions, and debris flow signals. Satellite observations throughout the week show an intense thermal anomaly from lava fountaining, lava flow, and collapse of the lava flow front.

A continous volcanic ash and gas plume has been reported by ground observers, pilots, and in satellite images since August 28. The height of the eruption plume has varied but has generally been between 12,000 to 16,000 ft (3.7 to 4.9 km) above sea level (ASL). A more vigorous plume to 20,000 ft (6.1 km) ASL with associated lighting (indicative of volcanic ash) was reported by NWS observers in Cold Bay on August 30 at 21:30 ADT (05:30 UTC on August 31). In response, the National Weather Service issued an Ashfall Advisory and Marine Weather Statement. There were no reports of ash fall and the Advisory was cancelled at approximately 01:00 ADT August 31.

If activity continues to increase, larger ash clouds that could affect higher-flying aircraft may be produced. The most immediate ground hazard in the vicinity of the volcano includes light ash fall on nearby communities. Previous historical eruptions from Pavlof caused only a few millimeters (about 1/10th of an inch) of ash to fall on King Cove, Nelson Lagoon, Cold Bay, and Sand Point. Mudflows in drainages from the flanks of the volcano, and lava flows and avalanching of hot debris on the upper reaches of the volcano are also of concern in the uninhabited areas around the volcano. Satellite and seismic data and eyewitness observations suggest most of the surface lava activity is occurring on the southeast sector of the steep-sided volcano; this suggests that the Pacific Ocean side of the volcano is at most risk from avalanching hot debris.

At this time, we expect this eruption to follow the pattern of previous eruptions. The last eruption of Pavlof began in September 1996 and consisted of a several-month-long series of ash explosions, lava-fountaining, and lava-flow production. Ash clouds reached as high as 30,000 ft asl on one occasion. However, most ash clouds were below 20,000 ft asl. Prior to 1996, Pavlof erupted in 1986 sending ash as high as 49,000 ft asl on at least one occasion. A hazard assessment for Pavlof and the Emmons Lake volcanic center is available on the web at http://www.avo.alaska.edu/pdfs/SIR2006-5248.pdf

Pavlof volcano is located on the southwestern end of the Alaska Peninsula. Pavlof is a stratovolcano which rises to an elevation of 8262 feet. With almost 40 historic eruptions, it is one of the most consistently active volcanos in the Aleutian arc. Eruptive activity is generally characterized by sporadic strombolian fountaining continuing for a several-month period. The community of Cold Bay is located 60 km (37 miles) to the southwest of Pavlof.

CLEVELAND VOLCANO (CAVW#1101-24-)
52°49′20″ N169°56′42″ W, Summit Elevation 5676 ft (1730 m)
Current Aviation Color Code: ORANGE
Current Volcano Alert Level: Watch

Periodically throughout the week satellite views showed a persistent thermal anomaly at Cleveland’s summit. Web camera views were cloudy all week.

AVO continues to monitor the volcano closely with satellite imagery as weather allows. The lack of a real-time seismic network at Cleveland means that AVO is unable to track local earthquake activity related to volcanic unrest. Short-lived explosions of ash that could exceed 20,000 ft above sea level can occur without warning and may go undetected on satellite imagery.

Cleveland volcano forms the western half of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. It is located about about 75 km (45 mi.) west of the community of Nikolski, and 1500 km (940 mi.) southwest of Anchorage. The volcano’s most recent significant eruption began in February, 2001 and had 3 explosive events that produced ash clouds as high as 12 km (39,000 ft) above sea level. This eruption also produced a rubbly lava flow and hot avalanche that reached the sea. The most recent minor ash emissions were observed in October 2006.

KOROVIN VOLCANO (ATKA ISLAND) (CAVW#1101-16)
52°22′48″ N174°9′22″ W, Summit Elevation 5030 ft (1533 m)
Current Aviation Color Code: YELLOW
Current Volcano Alert Level: Advisory

Intermittent, low-level seismic activity continued at Korovin. Satellite views were cloudy all week.

Korovin has erupted several times in the past 200 years, most recently in 1998. Eruptions typically produce minor amounts of ash and occasional, small lava flows. Ash plume heights could exceed 20,000 ft above sea level. Korovin occasionally produces large steam plumes from its summit.

Korovin Volcano is a 1553-m-high (5030 ft) stratovolcano located on the northern part of Atka Island in the central Aleutian Islands, about 184 km (110 mi) east of Adak, 538 km (350 mi) west of Dutch Harbor, and 1760 km (1100 mi) southwest of Anchorage. The volcano has two distinct summit vents about 0.6 km (2000 ft) apart, that have been the sites of eruptive activity as recently as June, 1998. The most recently active of the vents maintains a small, roiling, lake that occasionally produces energetic steam emissions. Thermal springs and fumaroles located on and near the volcano indicate an active hydrothermal system. Korovin has erupted several times in the past 200 years, including 1907, 1951, 1953, 1954, 1973, 1976, 1986, 1987, 1996, and 1998. All of these eruptions produced minor amounts of ash and occasional but small lava flows. Reports of the height of the ash plume produced by the 1998 eruption ranged from 4900 to 9200 m (16,000 to 30,000 feet) above sea level.

OTHER ALASKA VOLCANOES

Seismic activity is monitored in real time at 31 volcanoes in Alaska. Satellite images of all Alaskan volcanoes are analyzed daily for evidence of ash plumes and elevated surface temperatures. Some volcanoes may currently display anomalous behavior but are not considered to be at a dangerous level of unrest. Wrangell, Spurr, Redoubt, Iliamna, Augustine, Fourpeaked, Snowy, Griggs, Katmai, Novarupta, Trident, Mageik, Martin, Ugashik-Peulik, Ukinrek Maars, Aniakchak, Veniaminof, Dutton, Isanotski, Shishaldin, Fisher, Westdahl, Akutan, Makushin, Okmok, Great Sitkin, Kanaga, Tanaga, and Gareloi volcanoes are at Aviation Color Code GREEN and Volcano Alert Level NORMAL. All are at or near normal levels of background seismicity. AVO did not detect ash plumes or significant elevated surface temperatures in the vicinity of any volcano.

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