Augustine Volcano - John Seach



58.77 N, 153.68 W
summit elevation 2104 m

Augustine Volcano is located in southwestern Cook Inlet about 280 kilometers southwest of Anchorage, Alaska. It is the most active of the eastern Aleutian volcanoes of Alaska. The volcano forms most of Augustine Island, an 8- by 11-kilometer, nearly circular island composed mostly of volcanic deposits.

Captain James Cook named the volcano when he first observed it on St. Augustine’s Day in 1778.

The volcano contains summit lava domes and debris-avalanche and pyroclastic-flow deposits. At least 11 large debris avalanches have reached the sea during the past 2000 years. All known eruptions have occurred from a central conduit.

Augustine is possibly the youngest volcano in the Cook Inlet. The volcano began forming 25,000 to 40,000 years ago. At least 13 debris avalanches have occurred in the past 2500 years, which were the result of lava dome collapse.

Eruptions usually begin with a violent, vent-clearing phase associated with pyroclastic flows, vertical eruption plumes of ash and steam, and extensive ash fall. This is followed by lava dome extrusion, collapse, and hot block and ash flows.

2016 Earthquake
A magnitude 7.1 earthquake occurred 25 km north of Augustine volcano on 24 January 2016.

2006 Eruptions
Explosive eruptions began at Augustine on 11 January 2000, after an increase in seismicity at the volcano. An ash plume reached an altitude of 30,000 ft. Volcanic mudflows occurred on the E, S, and W sides of the volcano. Small rock and snow avalanche deposits were visible high on the SW part of the volcano. On 27th January, an eruption sent ash to 40,000 ft. During 1-7 February, pyroclastic flows continued to travel down the flanks, and ash plumes reached 15,000 ft altitude. Low level eruptions continued until April 2006.

1986 Eruptions
Between August 1985 and late February 1986 there were 12 earthquakes at Augustine volcano per day. On 17th February 1986 an explosive eruption was observed at the volcano with a plume reaching an altitude of 3 km. From 27-31 March 1986 large explosions sent eruption clouds into the stratosphere and produced pyroclastic flows that reached the sea. Flights were diverted from the area. On 29th March, a DC-10 airline experienced windscreen and turbine abrasion from volcanic ash while descending to Anchorage airport. A sulphur dioxide plume covered an area of 250 km diameter between Augustine volcano and Anchorage. By 24th April a new dome had formed in the crater, and hot rock avalanches were occurring down the NW side. The 1986 eruption was different from previous eruptions because there was no vent clearing explosion at the beginning.

1976 Eruptions
Explosive eruptions began on 22nd January 1976. Five large eruptions occurred over the next 3 days. Ash emissions reached a height of 14 km. Pyroclastic flows reached the sea on the S and NE sides of the volcano. Eruptions also occurred in mid-February, and mid-April. During July and August there was degassing from the lava dome, and no new eruptions.

1883 Eruptions
This was the largest historical eruption at Augustine volcano. Residents on Augustine Island felt strong earthquakes and evacuated the island prior to the eruption. The paroxysmal phase of the eruption began at 0800 hr on 6th October 1993. Residents of English Harbor (English Bay or Port Graham) on the Kenai Peninsula 85 km from the volcano heard a large explosion and saw dense emissions from the summit. A 9 m high tsunami hit Port Graham 25 minutes after the eruption. The tsunami occurred at low tide, and there were no fatalities. The tsunami was caused by collapse of the upper edifice of Augustine, which produced a debris avalanche that reached the sea.

1540 ± 100 years Eruption
A lateral blast accompanied failure of the northwest flank of Augustine about 1540 (± 100 years). The eruption formed the West Island debris-avalanche deposit.

Augustine Volcano Eruptions

2006, 1986, 1976-77, 1971, 1964-65, 1935, 1883, 1812, 1650 ± 100, 1540 ± 100, 1200 ± 75, 890 AD ± 150, 510 AD ± 200, 230 AD ± 20.