HIGHWAY 101 LANDSLIDE: IT COMES WITH THE TERRITORY

By Adam Spencer, The Triplicate December 10, 2012 06:21 pm

 Work continues Friday to clear the slide that has reduced traffic to one lane on U.S. Highway 101 since last weekend.
Work continues Friday to clear the slide that has reduced traffic to one lane on U.S. Highway 101 since last weekend. Del Norte Triplicate / Adam Spencer
 The luscious mountain ridges that paint Del Norte’s horizons to the east are growing just as fast as your fingernail. In fact, experts say the Coast Range and Klamath Mountains would be taller than the Himalayas if it wasn’t for all that natural erosion.  

Like the kind of massive erosion demonstrated recently by an impressive landslide on U.S. Highway 101 about three miles south of Crescent City.

Caltrans officials said that the highway is expected to return to two-way traffic by Tuesday evening — more than a week after last Saturday’s slide closed the northbound lane.

Redwood National & State Parks Superintendent Jeff Bomke said it was the largest slide with old growth redwoods he has seen in more than 30 years on the North Coast. A redwood roughly 5 feet in diameter was toppled.

Redwoods fall over regularly as part of the natural forest process, Bomke said. Three fallen redwoods briefly closed U.S. Highway 199 last week during the same storm that caused the slide.  But landslides taking down old growth are “fairly rare,” he said.

Still, landslides are very common to our region.

Just ask Michael Furniss, a hydrologist with the U.S. Forest Service’s Pacific Northwest Research Station and adjunct professor at Humboldt State University.

“The big picture is that the landscape is rising long term at about the rate that a fingernail grows, and over time this really adds up. It grows steeper and steeper and eventually something has to give way,” Furniss said.

The rapid uplift of the Coast Range and Klamath Mountains is one of the main elements that makes erosion and landslides so common to the region.

“The natural erosion process is what balances that uplift,” Furniss said.

Besides the fast uplift, frequent and heavy rains, deep soils and a fractured bedrock contribute to our landslide trends.

After the heavy rains that caused the 1964 Christmas flood, Furniss said that landslides “were all over the place.”

“There was thousands of them and most road systems were inaccessible,” he said.

There was so much debris in drainages from landslides that even small streams rose 20 to 30 feet, Furniss said.  Those streams have since carved a path through the muck, but the terraces that were created can still be seen.

Although Crescent City received more than 4 inches of rain in a 24-hour period from a storm last week, it was the series of storms that created the perfect conditions for the 101 landslide.

“In long-duration, soaking storms — with one storm after the other — the water pressure builds up on the slope and lifts them up and they slide,” Furniss said. “The wetter they get, the less friction there is, then gravity wins and down it goes.”

All that water creates a “buoyant force” that makes the slope float up in a way, decreasing friction and increasing the likelihood of a slide, Furniss said.

Caltrans officials said they will evaluate the area for future management after all the debris is cleared, but in this terrain, landslides are almost unavoidable.

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