The Osceola Mudflow, also known as the Osceola Lahar, was a

lahar A lahar (, from jv, ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley. Lahars are extr ...

in the U.S. state of

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

that descended from the summit and northeast slope of

Mount Rainier Mount Rainier (), indigenously known as Tahoma, Tacoma, Tacobet, or təqʷubəʔ, is a large active stratovolcano in the Cascade Range of the Pacific Northwest, located in Mount Rainier National Park about south-southeast of Seattle. With a ...

during a period of eruptions about 5,600 years ago. It traveled down the west and main forks of the White River, passed the location of present-day

Enumclaw Enumclaw ( ) is a city in King County, Washington, United States. The population was 12,543 at the 2020 census. The Enumclaw Plateau, on which the city resides, was formed by a volcanic mudflow ( lahar) from Mount Rainier approximately 5,700 ...

then reached

Puget Sound Puget Sound ( ) is a sound of the Pacific Northwest, an inlet of the Pacific Ocean, and part of the Salish Sea. It is located along the northwestern coast of the U.S. state of Washington. It is a complex estuarine system of interconnected m ...

near present-day Auburn. The Osceola collapse formed a wide horseshoe-shaped crater, open to the northeast, almost the same size as the crater produced by the

1980 eruption of Mount St. Helens On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated until a major explosive er ...

. Most of the Osceola crater has been filled in by subsequent lava eruptions, most recently about 2,200 years ago. With a volume of and an areal extent of about , the Osceola Mudflow buried a large portion of the Puget Sound lowland with hydrothermally altered volcanic material. Many communities in

King King is the title given to a male monarch in a variety of contexts. The female equivalent is queen regnant, queen, which title is also given to the queen consort, consort of a king. *In the context of prehistory, antiquity and contempora ...

and Pierce

counties A county is a geographic region of a country used for administrative or other purposesChambers Dictionary, L. Brookes (ed.), 2005, Chambers Harrap Publishers Ltd, Edinburgh in certain modern nations. The term is derived from the Old French ...

, notably

Kent Kent is a county in South East England and one of the home counties. It borders Greater London to the north-west, Surrey to the west and East Sussex to the south-west, and Essex to the north across the estuary of the River Thames; it faces ...

, Enumclaw, Orting, Buckley, Sumner,

Puyallup Puyallup may refer to: * Puyallup (tribe), a Native American tribe * Puyallup, Washington, a city ** Puyallup High School ** Puyallup School District ** Puyallup station, a Sounder commuter rail station ** Washington State Fair, formerly the ...

and Auburn, are wholly or partly located on top of Osceola Mudflow deposits. The Osceola Mudflow was Mount Rainier's signature event during the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided ...

. It was named after the unincorporated community of

Osceola Osceola (1804 – January 30, 1838, Asi-yahola in Muscogee language, Creek), named Billy Powell at birth in Alabama, became an influential leader of the Seminole people in Florida. His mother was Muscogee, and his great-grandfather was a S ...

References

Lahars Mount Rainier Geology of Washington (state) Landslides in the United States Prehistoric volcanic events Holocene events {{volcanology-stub