Cowlitz River Views

Highwater along the Cowlitz River, as seen from Castle Rock, Washington USGS Photo by T. Leighley, February 20, 1982

View eastward to U. S. Interstate Highway 5 bridge and confluence of the Cowlitz and Toutle Rivers. Here, the lahar from the South Fork Toutle entered the Cowlitz River at 1:00 p.m. P.D.T. on May 18, 1980. The lahar from the North Fork Toutle River arrived at the mouth of the Toutle River at about 8:30 p.m., where it was described as having a homogeneous, mortarlike consistency from bank to bank. The early part of the lahar past this point was seen to carry logs, buildings, and a pickup truck. As the lahar entered the Cowlitz River, the main mass moved downstream, but part moved upstream for 2.5 miles. Logs from the flow were deposited onto the Burlington Northern Railroad bridge, and U.S.Interstate Highway 5 was closed to traffic.

-- Excerpts from: Doukas, 1990, Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington: USGS Bulletin 1859, 53p.

Cowlitz River Bridge

During the May 18, 1980, eruption (of Mount St. Helens) and subsequent flooding, the effects of the South Fork Toutle River lahar were scarcely noticed here (from the bridge). At 1:30 p.m. P.D.T. the stage had risen to 13.15 feet, but by 2:15 p.m. it had returned to the preflood condition of 10 feet. The high flow from the North Fork Toutle River lahar was recorded at the Castle Rock bridge at midnight, nearly 15.5 hours after the 8:32 a.m. eruption. High-water temperature here was 85 degrees F. To your left as you leave the bridge is the Cowlitz County Fairgrounds (west of I-5). From 3 to 5 feet of sediment was deposited over the entire fairgrounds by the flood on May 18-19, 1980.

-- Excerpts from: Doukas, 1990, Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington: USGS Bulletin 1859, 53p.