Highway 30 just east of Astoria reopened to one lane on Jan. 5 following a rock and mud slide that closed the busy route early Monday morning, Jan. 4.
"The cause is excessive rainfall the past few days and saturated soils," Oregon Department of Transportation (ODOT) spokesman Lou Torres said. "We have many places on state highways along the coast, in the coast range and in the Cascades where we can get landslides, mudslides, rockfalls, etc. After all this is Oregon where we get lots of rainfall that falls on steep slopes."
Torres said motorists need to pay attention when driving along Highway 30 and other routes in landslide areas.
"The message is that this is winter in Oregon," he said. "Keep both hands on the steering wheel, mind on driving and eliminate distractions. Be prepared for winter driving conditions which can mean dealing with wet and icy roads, snow, high water and possibly rock and mud slides."
Torres added that road closures during the winter are a fact of life in the region and can’t be totally prevented.
"Always leave plenty of travel time, check TripCheck.com before you go and expect delays," Torres said.
The Oregon Department of Geology and Mineral Industries (DOGAMI) said the landslides can be caused by several factors, including the type of geology, the slope and water. Rainwater buildup following frequents storms can lead to a landslide.
According to a DOGAMI executive summary report about landslides and debris flows, the events are common in the Oregon Coast Range due to the combination of high precipitation, steep slopes, and landslide-prone geologic units. Cutting through the northern Coast Range, the U.S. Highway 30 (Oregon State Highway 92) corridor is prone to slope instability.
DOGAMI lists the following for precautions and safety.
People, structures and roads located below steep slopes in canyons and near the mouths of canyons may be at serious risk. Dangerous places can include:
• Canyon bottoms, stream channels, and areas of rock and soil accumulation at the outlets of canyons.
• Bases of steep hillsides.
• Road cuts or other areas where slopes of hills have been excavated or over-steepened.
• Places where slides or debris flows have occurred in the past.
According to DOGAMI’s A Homeowners Guide to Landslides, a landslide is the downward slope movement of rock, soil or debris. Debris flow, earth flow, rock fall, mudflow, mudslide, and slump are also terms for landslide.
Landslides can take human life. However, even a few inches of slope movement can disrupt septic, sewer and water lines and crack foundations severely damaging or destroying your home, according to the guide.
If you live on or near a steep slope, the guide encourages you to look for warning signs of landslides by evaluating your property for signs of landslide movement. Many, but not all, signs of landslide activity are listed below. A high score may indicate the presence of a landslide.
Inside Your Home:
Cracks in walls
Nails popping out of walls
Separation of chimney from walls
Light switches coming out of walls
Doors/windows hard to shut
Cracks in floors
Water seeping into basement
Outside Your Home:
Changes in surface drainage
Bulges in retaining walls or tilting of walls
Cracks developing in the soil
Pistol-butted or bent trees
Broken water, utility, or sewer lines
Cracks in sidewalks or foundation
Stretched or leaning utility lines
The guide also recommends actions property owners can take to reduce the chances of landslides, which include:
• Draining water from surface runoff, downspouts, and driveways well away from slopes.
• Planting native ground cover on slopes.
• Consulting with a professional before significantly altering existing slopes uphill or downslope of your home.