Aldercrest-Banyon landslide
Encyclopedia
The Aldercrest-Banyon landslide was a major slow-moving landslide
in the east Kelso, Washington
neighborhood of Aldercrest beginning in early 1998 through 1999. The disaster ended up being one of the worst urban landslides in United States
history in terms of cost. The landslide is one of the most famous in Washington state, which has many landslides due to it’s mountainous terrain. The Aldercrest-Banyon landslide was the first landslide disaster in the United States that the Federal Emergency Management Agency
(FEMA) to be declared an official disaster area.
(15,300–12,700 years ago). Approximately 2 to 14 million years ago, the Columbia River
deposited gravels, sands, silts, and clays and are known as the Troutdale Formation. In the area of the landslide, along a northwest-southeast trending ridge about one-half mile east of Interstate 5, the Troutdale Formation ranges from approximately 40 to 500 feet thick in the Kelso area and was deposited upon a much older, near-shore marine sedimentary deposit known as the Cowlitz Formation. These areas are known for landslide activity. At the base of the slope is the Coweeman River
.
In mid-April 1998, 2.5 to 6 foot high crack developed on the natural slope causing the evacuation of two homes. The city of Kelso did it’s best to repair roads and moved utilities above ground so residents could stay in their homes for as long as possible.
Movement of the upper slope gradually increased into a continuous headscarp approximately 1500 feet long with a vertical separation of 30 feet by June 1998. The landslide is about 3000 feet (915 m) wide by 1500 feet (457 m) in length had reached the height of 125 feet. In June 1998, 54 homes were located within the active limits of the landslide and during the winter of 1998-1999, 3 more homes were swallowed up. The maximum slide movement in 1998 was about 6 to 12 inches (15 to 30 cm) per day
On October 16, 1998, President Bill Clinton
and the Federal Emergency Management Agency issued a Presidential Disaster Declaration. Some assistance was then given to the affected residents. The city of Kelso condemned 137 homes and dispersed roughly 4.7 million in FEMA funds to those evacuated.
in Palos Verdes Hills
of Southern California
, when 130 homes were destroyed. All but eleven homeowners took the offer accepting the risk that the upper ridge of possibly reactivating. The federal government has removed all of the purchased homes.
In 2000, in response to the Aldercrest–Banyon and other recent damaging landslides in Cowlitz County, the Washington Division of Geology and Earth Resources began a geographic information systems
-based landslide inventory and slope stability mapping project. In total, 260 square miles (680 km2) of urbanizing lands in Cowlitz County between the Toutle River
and the Lewis
and Wahkiakum County
lines have been mapped for all landslides, regardless of age.
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
in the east Kelso, Washington
Kelso, Washington
Kelso is a city in southwest Washington State, United States, and is the county seat of Cowlitz County. At the 2010 census, the population was 11,925. Kelso is part of the Longview, Washington Metropolitan Statistical Area, which has a population of 102,410. Kelso shares its long western border...
neighborhood of Aldercrest beginning in early 1998 through 1999. The disaster ended up being one of the worst urban landslides in United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
history in terms of cost. The landslide is one of the most famous in Washington state, which has many landslides due to it’s mountainous terrain. The Aldercrest-Banyon landslide was the first landslide disaster in the United States that the Federal Emergency Management Agency
Federal Emergency Management Agency
The Federal Emergency Management Agency is an agency of the United States Department of Homeland Security, initially created by Presidential Reorganization Plan No. 1 of 1978 and implemented by two Executive Orders...
(FEMA) to be declared an official disaster area.
History
The 80-acre Aldercrest residential neighborhood was completed in three phases between 1973 and 1979. It is built on an ancient landslide that may have occurred during the Missoula floodsMissoula Floods
The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...
(15,300–12,700 years ago). Approximately 2 to 14 million years ago, the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...
deposited gravels, sands, silts, and clays and are known as the Troutdale Formation. In the area of the landslide, along a northwest-southeast trending ridge about one-half mile east of Interstate 5, the Troutdale Formation ranges from approximately 40 to 500 feet thick in the Kelso area and was deposited upon a much older, near-shore marine sedimentary deposit known as the Cowlitz Formation. These areas are known for landslide activity. At the base of the slope is the Coweeman River
Coweeman River
The Coweeman River is a tributary of the Cowlitz River, in the U.S. state of Washington. Its name comes from the Cowlitz word ko-wee-na, meaning "short one", referring to a short Indian who once lived along the river.-Course:...
.
The Landslide
Following 3.5 years of above average rainfall the water loosened layers of clay but did not percolate through, and the load on the earth was increased. The Troutdale and Cowlitz formations began to slip. Also a road excavation in February 1998 across the lower part of the slide may have been a trigger to cause the initial reactivated movement, which then caused storm drains to break and storm water to be fed back into the slide. Logging operations at the toe of the landslide may also have contributed to the reactivation. Aldercrest-Banyon residents began to see signs of ground movement. In February 1998 underground utilities began to break from the pressure and once broken storm drains fed abundant water into the system, it further increased the earth movement rates. By March homes began to show signs of movement and stress. These included jammed doors and windows, and concrete foundations cracking. Other signs were separation of chimneys from foundations, drywall bulging over nailheads, twisted ceiling beams, water flowing thru foundation cracks, bulging walls, kitchen cabinets separating from the walls and creaking, popping and snapping noises could be heard in the homes.In mid-April 1998, 2.5 to 6 foot high crack developed on the natural slope causing the evacuation of two homes. The city of Kelso did it’s best to repair roads and moved utilities above ground so residents could stay in their homes for as long as possible.
Movement of the upper slope gradually increased into a continuous headscarp approximately 1500 feet long with a vertical separation of 30 feet by June 1998. The landslide is about 3000 feet (915 m) wide by 1500 feet (457 m) in length had reached the height of 125 feet. In June 1998, 54 homes were located within the active limits of the landslide and during the winter of 1998-1999, 3 more homes were swallowed up. The maximum slide movement in 1998 was about 6 to 12 inches (15 to 30 cm) per day
On October 16, 1998, President Bill Clinton
Bill Clinton
William Jefferson "Bill" Clinton is an American politician who served as the 42nd President of the United States from 1993 to 2001. Inaugurated at age 46, he was the third-youngest president. He took office at the end of the Cold War, and was the first president of the baby boomer generation...
and the Federal Emergency Management Agency issued a Presidential Disaster Declaration. Some assistance was then given to the affected residents. The city of Kelso condemned 137 homes and dispersed roughly 4.7 million in FEMA funds to those evacuated.
Aftermath and Damage
The homes and infrastructure suffered more than $70 million of destruction. FEMA and the state of Washington offered to buyout 127 homeowners at 30 cents on the dollar. This was the second largest landslide disaster in US history involving homes on a landslide. The largest was the 1956 Portuguese Bend LandslidePortuguese Bend
The Portuguese Bend region is the largest area of natural vegetation remaining on the Palos Verdes Peninsula, in Los Angeles County, California....
in Palos Verdes Hills
Palos Verdes Hills
The Palos Verdes Hills are a mountain range on the south coast of Los Angeles County, California.They are the landed end of the Channel Islands of California Transverse Ranges formation, and are the location of Palos Verdes Estates, Rolling Hills, and other communities.The South Coast Botanic...
of Southern California
Southern California
Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...
, when 130 homes were destroyed. All but eleven homeowners took the offer accepting the risk that the upper ridge of possibly reactivating. The federal government has removed all of the purchased homes.
In 2000, in response to the Aldercrest–Banyon and other recent damaging landslides in Cowlitz County, the Washington Division of Geology and Earth Resources began a geographic information systems
Geographic Information System
A geographic information system, geographical information science, or geospatial information studies is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data...
-based landslide inventory and slope stability mapping project. In total, 260 square miles (680 km2) of urbanizing lands in Cowlitz County between the Toutle River
Toutle River
The Toutle River is a river in southwestern Washington State, in the Pacific Northwest region of the United States. It rises in two forks on the flanks of Mount St. Helens and joins the Cowlitz River near Castle Rock.-Eruption of Mount St. Helens:...
and the Lewis
Lewis County
Lewis County is the name of seven counties in the United States:* Lewis County, Idaho* Lewis County, Kentucky* Lewis County, Missouri* Lewis County, New York* Lewis County, Tennessee* Lewis County, Washington* Lewis County, West VirginiaSee also:...
and Wahkiakum County
Wahkiakum County
Wahkiakum County may refer to:Places*Wahkiakum County, WashingtonShips*USS Wahkiakum County , a United States Navy landing ship tank in commission from 1953 to 1970...
lines have been mapped for all landslides, regardless of age.
See Also
- Washington Department of Natural ResourcesWashington Department of Natural ResourcesThe Washington Department of Natural Resources manage over of forest, range, agricultural, and commercial lands for the people of Washington State. DNR also manages of aquatic areas which include shorelines, tidelands, lands under Puget Sound and the coast, and navigable lakes and rivers...
- List of Landslides