Lahars that formed during the 1989-90 eruptions of Redoubt Volcano in Alaska accumulated in the Drift River Valley NE of the volcano. The largest lahars, such as this one from the February 15, 1990 eruption, covered the valley floor nearly wall-to-wall and extended more than 35 km to the Cook Inlet.
Pyroclastic-flow deposits from the April 15 (lower 2/3 of section) and April 21 (upper 1/3 of section), 1990 eruptions of Redoubt Volcano in Alaska are exposed in a gully along the western margin of the piedmont lobe of Drift glacier. The shovel at the base of the section provides scale. The somewhat larger April 15 pyroclastic flow carried large blocky fragments of a lava dome that had been growing in the summit crater.
This oblique view from the north shows the final lava dome of the 1989-90 eruption of Alaska's Redoubt Volcano as it appeared approximately one year after the end of the eruption. The dome measures approximately 350-400 m across and represents an estimated 10 million cubic meters of material. Snow is accumulating on the cooling lava blocks although some hydrothermal activity continues to produce intermittent steam plumes. Periodic lava dome growth during the eruption was punctuated by strong explosions that destroyed earlier lava domes.
An Alaska Volcano Observatory geologist uses a laser-surveying instrument to measure distances to targets installed on the flanks of Redoubt Volcano. Minute changes in distances to the targets can reflect ground deformation that may indicate magma movement. Steam rises above a lava dome in the crater of Redoubt in this photo taken on May 5, 1990, near the end of an eruption that had begun the previous December.
An Alaska Volcano Observatory geologist sets up GPS (Global Positioning System) instrumentation on the north flank of Redoubt Volcano. The GPS receiver calculates an extremely accurate location through satellite-based triangulation. This helps pinpoint locations for electronic distance measurements that detect deformation of the volcano related to eruptive activity. The Drift River valley extending away from the volcano to the NE was covered with pyroclastic-flow and mudflow deposits from the 1989-90 eruption.
