A volcanologist observes a large, 6-m-high block that was carried about 4 km down the north flank of Augustine volcano in Alaska during the 1976 eruption. Blocks of this size and larger are fragments of the summit lava dome that were carried within block-and-ash flows produced by periodic collapse of the growing dome. This photo was taken during a quiet phase of the 1986 eruption and shows the steaming summit lava dome.
Collapse of the summit and flank of a volcano can produce massive volcanic landslides. The resulting highly mobile debris avalanches rapidly sweep down the volcano and far beyond its flanks. These small hills in the foreground of Alaska's Augustine volcano show a morphology common to debris-avalanche deposits. The hummocks consist of relatively intact segments of the volcanic edifice that were transported long distances without disaggregating. This debris avalanche traveled roughly 11 km from the summit about 450 years ago.
Volcanologist Jurgen Kienle hoists a light-weight block of pumice at the toe of a 1986 pyroclastic-flow deposit at Alaska's Augustine volcano. A pyroclastic-flow apron was formed by the accumulation of many individual lobes. Thermal measurements more than 100 days after the eruption showed a maximum temperature of 525 degrees Centigrade at a depth of 6 m. Pumiceous pyroclastic flows during the 1986 eruption traveled about 5 km from summit and reached the sea on the north and NE coasts of Augustine Island.
This wave-cut section exposes the interior of the Burr Point debris-avalanche deposit from the 1883 eruption of Augustine volcano. The color mottling, which results from the transport of discrete segments of the volcano that are not thoroughly mixed, is a characteristic texture of debris-avalanche deposits. The scale bar is 2-m high.
A pyroclastic flow sweeps down the north flank of Augustine volcano in Alaska on March 30, 1986, 3 days after the start of a 5-month long eruption. A large convecting ash column rises above the moving pyroclastic flows. As with many Augustine eruptions, early pyroclastic flows were pumice rich; later in the eruption block-and-ash flows were produced by collapse of a growing lava dome.