Printer friendly versionALASKA VOLCANO OBSERVATORY
Tuesday, August 23, 2005 1:45 PM AKDT (21:45 UTC)
57°8.1’N 156°59.4’W, Summit Elevation 7,005 ft (2,135 m)
Current Level of Concern Color Code: Not Assigned
An AVO field crew reports that a 1,300 ft (400 m) wide melt-water lake has formed in the snow and ice filled summit crater at Chiginagak Volcano sometime since the last observations in August 2004. Sometime earlier this summer, the southern crater rim of Chiginagak was breached, allowing a portion of the lake to drain. The resulting lahar (a debris flow consisting of a mixture of volcanic sediment, water, and ice) left a deposit on the unnamed glacier draining the crater to the south and caused flooding of 3 to 6 ft (1 to 2 m) above normal on Indecision Creek. Volcano Creek and Mother Goose Lake, the headwaters of King Salmon River, were affected as well. Floodwaters also flowed on and through Chiginagak’s southeast glacier, spilling out into an unnamed Pacific drainage leading to Chiginagak Bay. The lahar likely contained acidic water. Although we have no direct samples of the summit lake water, measurements from crater lakes at similar volcanoes have shown pH values ranging from 0 to 3, the acidity arising mainly from sulfuric acid. Vegetation damage was observed along Indecision Creek and the unnamed Pacific drainage.
The breach in the crater rim and the ensuing lahar probably occurred in July 2005; reports from Painter Creek Lodge at this time tell of strong sulfur smells and cloudy, yellowish water in the Indecision Creek drainage
AVO geologists continue to investigate the event and its impacts. There are no indications that an eruption is imminent or that this event is necessarily precursory to an eruption.
Chiginagak Volcano is not seismically monitored. The nearest seismic networks are at Aniakchak and Ugashik-Peulik Volcanoes, both about 50 miles (80 km) away. It is AVO policy not to assign a color code of Green to a volcano without a real-time seismic network.
Chiginagak is a symmetric stratovolcano located 175 km (110 mi) south of King Salmon on the Alaska Peninsula. The nearest settlement is Pilot Point, 60 km (37 mi) to the northwest. The high flanks of the volcano are snow-and ice-covered, and a prominent fumarole located high on the north flank at about 5,500 ft (~1,675 m) constantly emits steam and sulfur gases. Historical eruptive activity has been minor and is poorly documented, however, the volcano is surrounded by pyroclastic deposits and lava flows that are likely less than a few thousand years old
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RECORDING ON THE STATUS OF ALASKA'S VOLCANOES (907) 786-7478
Tom Murray, Scientist-in-Charge, USGS
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Steve McNutt, Acting-Coordinating Scientist, UAF-GI
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The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.