Oso landslide: building toward disaster

Building toward disaster

The decades preceding the deadly landslide near Oso reflect a shifting landscape with one human constant: Even as warnings mounted, people kept moving in. This interactive graphic tells that story, starting in 1887. Thirteen aerial photographs from the 1930s on capture the geographical changes; the hill is scarred by a succession of major slides while the river at its base gets pushed away, only to fight its way back. This graphic lets you go back in time and track the warnings from scientists; the failed attempts to stabilize the hill; the logging on or near the unstable slope; and the 37 homes that were built below the hill only to be destroyed.

Glossary

Clear-cut - A type of logging in which most or all of the trees are removed.
Crib wall - A barrier built with logs lashed together with wire cable and anchored with buried, concrete blocks. Woody debris is sometimes added to slow the current and create pools for fish.
Department of Ecology - The state agency that regulates water quality.
DNR - The Department of Natural Resources, the state angency that regulates logging.
Fisheries Department - The state agency that regulated commercial fishing (food fish); it's now part of the Department of Fish & Wildlife.
Game Department - The state agency that regulated sport fishing (game fish); it's now part of the Department of Fish & Wildlife.
Geomorphologist - A geomorphologist studies landscape dynamics, investigating how geological processes such as landslides have sculpted the earth.
North Fork - Forty-five miles long, the North Fork of the Stillaguamish joins with the South Fork in Arlington; from there the river — the "Stilly," for short — flows to Puget Sound.
Scarp - Also called an escarpment, this is a steep, exposed face formed by erosion or sliding.
Slide Hill - Scientists have used three names for the hill — Hazel Landslide, Steelhead Haven Landslide, Halterman Slide — all references to the hillside's constant movement. Some residents just called it Slide Hill.
Stillaguamish Tribe - With fishing rights secured by treaty, the tribe has worked to restore salmon runs in the Stillaguamish River, often teaming up with the state.
U.S. Army Corps of Engineers - A federal agency with civilians and soldiers, whose engineering tasks include reducing risks from natural disasters.
Whitman Bench - A two-square-mile plateau above the slope, with mostly subsurface drainage.

Sources

This graphic relied on reports, memos, correspondence and photos obtained from local, state and federal agencies, including:

State: The Department of Natural Resources; Department of Ecology; Game and Fisheries departments (both since folded into the Department of Fish & Wildlife); the Recreation and Conservation Office; Department of Transportation; and the University of Washington;
Federal: The U.S. Army Corps of Engineers; the U.S. Forest Service; the U.S. Geological Survey; and the U.S. Department of Agriculture;
Local: Snohomish County departments including Public Works; Emergency Management; Planning; Health; and the Assessor’s office.

Most of these records were obtained under the state’s Public Records Act or the U.S. Freedom of Information Act, or from the Washington State Archives.

Some reporting relied on mapping and geographical analysis; among other steps we cross-referenced aerial photos and utilized lidar imagery, which exposes landscape beneath vegetation. In three instances – 1947, 1955 and 1969 – we needed to combine two aerial images taken on the same day, which is why there’s a visible line or divider toward the top of the photos.

We researched newspaper archives and tapped books, videos and oral or written histories from people who studied the hill or lived in or visited this river valley. We also drew on news accounts from The Seattle Times, The (Everett) Herald and NBC News.

Oso's Slide Hill

Building toward disaster

Glossary

Sources

Credits