Redoubt Volcano rises to a dramatic 10,197 feet from nearby sea level. This stratovolcano is at the head of the Chigmit Mountains within Lake Clark National Park and Preserve. There have been eruptions in 1902, 1966, 1989-1990 and most recently in 2009.
Form and Structure
Redoubt Volcano is a steep-sided cone about 10 km in diameter at its base and with a volume of 30-35 km3. The volcano is composed of intercalated pyroclastic deposits and lava flows and rests on Mesozoic granitic rocks of the Alaska-Aleutian Range batholith. It has been moderately dissected by the action of numerous alpine glaciers. A 1.8-km-wide, ice-filled summit crater is breached on the north side by a northward-flowing glacier, informally known as the Drift Glacier, which spreads into a piedmont lobe in the upper Drift River Valley. The most recently active vent is located on the north side of the crater at the head of the Drift Glacier. Holocene lahar deposits in the Crescent River and Drift River valleys extend downstream as far as Cook Inlet.
Vapor emissions 1933, 1965, 1967?
Ash-rich explosions 1902, 1966, 1967-68?, 1989-90
Volcanism at Redoubt may have begun as much as 0.88 Ma ago, although the bulk of the cone has been built within the last 200,000 years. Extensive 3500-year-old lahar deposits fill the Crescent River valley and dam Crescent Lake. The oldest historical eruption occurred in 1902, when explosions were heard 175 km away and widespread ashfall was reported in the Cook Inlet basin. Vapor emissions were reported in May 1933 and JanuaryFebruary 1965. During late January and early February 1966, an explosive eruption produced ash plumes as high as 6100 m; an associated burst of meltwater caused destruction of the glacier draining north from the summit crater and subsequent flooding downstream as far as Cook Inlet. A “series of clouds” during January 1967 and five explosions during December 1967 through April 1968 were reported by Wilson and Forbes (1969).
The most recent eruption at Redoubt began with a major phreatomagmatic, vent-clearing explosion at 9:47 am on December 14, 1989 after less than 24 hours of intense precursory seismicity. Three more ash-rich explosions occurred the following day, December 15, with the last blast generating a pyroclastic flow down the Drift Glacier. The resulting debris flow contained entrained ice blocks as large as 10 m across and crested about 8 m above the river channel near the Drift River Oil Terminal, 35 km downstream. A Boeing 747 enroute from Amsterdam that flew into the ash cloud several hours after the eruption experienced complete engine failure and narrowly avoided tragedy when the crew successfully restarted the engines and safely landed in Anchorage.
These initial explosive events were just the first of 23 major explosive events between December 1989 and April 1990. Following the mid-December explosive phases, the crater vent emitted only minor ash and steam for the next 5-7 days. From December 22 to January 2, 1990, however, a large, over-steepened lava dome grew over the vent. At 5:48 pm on January 2, the first of two powerful explosions destroyed most of the dome and sent ash plumes to over 12 km. Massive block and ash avalanches down the Drift Glacier generated the largest debris flow of the eruption, completely covering the 2-km-wide valley floor and spilling into Cook Inlet. Flood waters entered the oil terminal, as much as 75 cm deep in some buildings, and caused a temporary halt in operations.
Three eruptions occurred in the next two weeks during which time the vent remained open. The January 8 event occurred with no precursory warnings and the resulting ashfall on the Kenai Peninsula disrupted commerce and transportation. Open-vent eruptions on January 11 and 16 resulted in minor debris flows down the Drift River.
After the January 16 eruption, another period of dome growth ensued through mid-February. This dome was smaller than the earlier dome but larger than succeeding domes (Miller, 1994). Early on February 15, the dome was destroyed in an explosive eruption that again sent a large debris flow down the Drift River and blanketed the lower Kenai Peninsula with ash. A pyroclastic flow and surge traveled down the canyon, across the piedmont lobe of Drift Glacier, and swept up the opposite valley wall 700 m topping the ridge. Flow down the Drift River was largely diverted into a side drainage that carried flood waters close to oil storage tanks at the downstream oil terminal prompting reinforcement of the containment dikes surrounding the tank farm. A new dome began growing immediately following the eruption.
On February 21, the new, but considerably smaller, dome was destroyed, marking the beginning of a new trend in eruptive behavior. Characteristically, small domes were emplaced and subsequently destroyed explosively or by gravitational collapse, resulting in debris avalanches down the now ice-free canyon leading down to the Drift River valley, and flooding down the Drift River. Ten such eruptions followed from February 24 to April 21 at 4 to 8 day intervals. Following the April 21 eruption, growth of the present lava dome began and continued through early June. During the next several months, seismic activity declined dramatically and only steam emissions and minor rock falls from the dome were recorded as the eruption came to an end.
The 1989-90 eruption of Redoubt seriously effected the populace, commerce, and oil production and transportation throughout the Cook Inlet region and air traffic as far away as Texas. Total estimated economic costs are $160 million, making the eruption of Redoubt the second most costly in U.S. history [at the time].
There are several communities within a 200 mile radius of the volcano that could be affected by an eruption.
|Ninilchik||47 mi (76 km) SE|
|Salamatof||48 mi (78 km) NE|
|Clam Gulch||49 mi (79 km) SE|
|Nikiski||50 mi (81 km) NE|
|Anchorage||108 mi (174 km) NE|
To learn more about volcanoes in Lake Clark National Park and Preserve, visit their Volcanoes page.
References: Text for the "Form and Structure" through "1989-1990 Eruptions" is from Catalog of Historically Active Volcanoes in Alaska (USGS).