Magnitude and frequency of lahars and lahar-runout flows in the Toutle-Cowlitz River system

Scott, K M

Title: Magnitude and frequency of lahars and lahar-runout flows in the Toutle-Cowlitz River system

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Abstract

The recurrence interval of a lahar or lahar-runout flow at least large enough to inundate flood plains 50 kilometers from Mount St. Helens is less than 100 years. Lahars are volcanic debris flows and their deposits; lahar-runout flows are the hyperconcentrated streamflow evolved from distal lahars. The recurrence interval is conditional on eruptive state and is based on the most recent 4,500 years of the volcano's approximately 40,000- to 50,000-year history. The 100-year recurrence interval is within a normal time frame for long-term planning. Therefore engineering works in the Toutle River system should be designed for lahars, as well as floods, of a particular frequency. Unlike a water flood, a lahar that has a flow depth at least 1 meter on flood plains can cause a significant part of the maximum possible damage. Trees are killed, many structures are inundated and made unusable even if they are not crushed by timber floating in the lahar, and agriculture is not feasible for periods of as much as several years. The largest lahar in this history of the watershed was formed by the bulking of the sediment in a flood surge that originated from breaching of a natural dam of ancestral Spiritmore »« less

Authors:: Scott, K M

Publication Date:: Sun Jan 01 00:00:00 EST 1989

OSTI Identifier:: 6165142

Resource Type:: Journal Article

Journal Name:: United States Geological Survey, Professional Paper; (USA)

Additional Journal Information:: Journal Volume: 1447-B

Country of Publication:: United States

Language:: English

Subject:: 58 GEOSCIENCES; WASHINGTON; WATERSHEDS; LANDSLIDES; AGRICULTURE; BUILDINGS; DAMAGE; ENGINEERING; FLOODS; FREQUENCY DEPENDENCE; HISTORICAL ASPECTS; HYDROLOGY; LAKES; LAYERS; MT ST HELENS; PLANNING; RIVERS; SIZE; SOLIDS FLOW; THICKNESS; TIME DEPENDENCE; TREES; VOLCANIC ROCKS; VOLCANISM; CASCADE MOUNTAINS; DIMENSIONS; DISASTERS; FEDERAL REGION X; FLUID FLOW; IGNEOUS ROCKS; INDUSTRY; MOUNTAINS; NORTH AMERICA; PLANTS; ROCKS; STREAMS; SURFACE WATERS; USA; 580000* - Geosciences

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                    Scott, K M. Magnitude and frequency of lahars and lahar-runout flows in the Toutle-Cowlitz River system.  United States: N. p., 1989. 
        Web.

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                    Scott, K M. Magnitude and frequency of lahars and lahar-runout flows in the Toutle-Cowlitz River system.  United States.

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                    Scott, K M. 1989.  
        "Magnitude and frequency of lahars and lahar-runout flows in the Toutle-Cowlitz River system".  United States.

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@article{osti_6165142,

  title        = {Magnitude and frequency of lahars and lahar-runout flows in the Toutle-Cowlitz River system},

  author       = {Scott, K M},

  abstractNote = {The recurrence interval of a lahar or lahar-runout flow at least large enough to inundate flood plains 50 kilometers from Mount St. Helens is less than 100 years. Lahars are volcanic debris flows and their deposits; lahar-runout flows are the hyperconcentrated streamflow evolved from distal lahars. The recurrence interval is conditional on eruptive state and is based on the most recent 4,500 years of the volcano's approximately 40,000- to 50,000-year history. The 100-year recurrence interval is within a normal time frame for long-term planning. Therefore engineering works in the Toutle River system should be designed for lahars, as well as floods, of a particular frequency. Unlike a water flood, a lahar that has a flow depth at least 1 meter on flood plains can cause a significant part of the maximum possible damage. Trees are killed, many structures are inundated and made unusable even if they are not crushed by timber floating in the lahar, and agriculture is not feasible for periods of as much as several years. The largest lahar in this history of the watershed was formed by the bulking of the sediment in a flood surge that originated from breaching of a natural dam of ancestral Spirit Lake. The flow had a peak discharge of 300,000 to 300,000 m{sup 3}/s at a distance of 30 to 50 km from the volcano, and was the first of four lake-breakout lahars that occurred during a span of several years near the end of Pine Creek time. This series of lahars is interpreted as an analog of the events that would have happened, without engineering intervention, after the 1980 eruption. In 1980, a debris avalanche catastrophically raised Spirit Lake more than 60 m and created new lakes in blocked tributaries.},

  doi          = {},

  url          = {https://www.osti.gov/biblio/6165142},
  journal      = {United States Geological Survey, Professional Paper; (USA)},
number       = ,

  volume       = 1447-B,

  place        = {United States},

  year         = {Sun Jan 01 00:00:00 EST 1989},

  month        = {Sun Jan 01 00:00:00 EST 1989}

}

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