Osceola Mudflow
The Osceola Mudflow, also known as the Osceola Lahar, was a
The Osceola flow began either as an avalanche or series of avalanches near the summit of Mount Rainier but had transformed to a lahar within 2 km (1.2 mi) of where it was initiated as it incorporated significant amounts of water from within the volcano's hydrothermal system.[1] The sector collapse formed a 1.8 km (1.1 mi) wide horseshoe-shaped crater, open to the northeast, almost the same size as the crater produced by the 1980 eruption of Mount St. Helens. Most of the Osceola crater has been filled in by subsequent lava eruptions, most recently about 2,200 years ago.[2]
With a volume of 3.8 km3 (0.91 cu mi) and an areal extent of about 550 km2 (210 sq mi), the Osceola Mudflow buried a large portion of the Puget Sound lowland with hydrothermally altered volcanic material that is estimated to have been traveling at 70 km/h (43 mph) up to 50 km (31 mi) downstream from the source region. Many communities in King and Pierce counties, notably Kent, Enumclaw, Orting, Buckley, Sumner, Puyallup and Auburn, are wholly or partly located on top of Osceola Mudflow deposits which reach a depth of up to 100 m (330 ft).[2] The flow may have buried embayments of Puget Sound.[1]
The Osceola Mudflow was Mount Rainier's signature event during the
.Age of the mudflow
The age of the mudflow has been determined by the
Source of the mudflow
Since 1898, geologists recognized that Mount Rainier was historically higher. In 1963, D.R. Crandell inferred that the “missing summit” had collapsed down the northeast side becoming the Osceola Mudflow. A semicircular amphitheater would have opened to the northeast. The depression then filled over time with ice (
Volume of the mudflow
The volume of the mudflow is estimated at 3.8 cubic kilometres (0.91 cu mi) from an examination of outcrops and well logs plus an estimation of the volume parcels from across the identified flow. The mudflow centers about 80 kilometres (50 mi) from Mount Rainier. The Osceola volume of 3.8 cubic kilometres (0.91 cu mi) plus the Paradise lahar of 0.05 to 0.1 cubic kilometres (0.012 to 0.024 cu mi) is more than the 2 to 2.5 cubic kilometres (0.48 to 0.60 cu mi) of the “missing summit.” The material would have expanded during the avalanche, and it would have added materials from along the route, accounting for the difference.[1] The Osceola debris underlies the
References
This article incorporates public domain material from websites or documents of the United States Geological Survey.
- ^ a b c d e f g h i Vallance, James W.; Scott, Kevin M. (February 1997). "The Oceola Mudflow from Mount Rainier: Sedimentology and hazard implications of a huge clay-rich debris flow" (PDF). Geological Society of America Bulletin: 143–163.
- ^ a b c "Significant Lahars at Mount Rainier". United States Geological Survey. 2014-11-10. Retrieved 2018-03-18.