The steep slope at Hogg Rock, along U.S. Highway 20 west of Sisters, is known to slide. Snow slides there have even blocked the highway, one of the main arteries through the Cascades, for a couple of days at a time.
“But it is not mud and debris, which is a whole different type of slide concept,” Peter Murphy, spokesman for the Oregon Department of Transportation in Bend said Wednesday.
Mud, muck and debris are what search teams are contending with in Oso, Wash., where a horrific landslide on March 22 buried a small community. As of Wednesday afternoon, The Associated Press reported the Oso landslide had killed at least 36 and the search continued for more bodies.
The Oso landslide has prompted conversations about the possibility of landslides elsewhere around the Northwest.
Landslides occur when there are the right set of circumstances, from geology to weather, said Ian Madin, the chief scientist for the Oregon Department of Geology and Mineral Industries. Some places around Central Oregon, such as the slopes of the Cascades or the hills around Prineville, could be prone to slide, but the lava flows around and under Bend are fairly stable.
“It is not a real high hazard (around Bend),” Madin said.
Understanding what the landslide danger in an area is requires looking at its past, and the clues left in the land. State scientists like Madin used to do this by driving around or scanning over aerial photos, searching for signs of slides. Nowadays they use high-tech laser technology to create detailed images of the landscape, but the time-consuming chore of looking for places in the images where there have been landslides remains much the same.
The agency has an online map showing where landslides have occurred, going back a few thousand years. But the map is far from complete. Madin said it shows about 25 percent of the historic landslide activity west of the Cascades and about 50 percent east of the mountains. The disparity comes from the old forms of data gathering — it was easier to see where there had been slides east of the Cascades because of lesser vegetation.
The laser images show the ground below vegetation, making it possible to see where there have been landslides even below thick woods. This will help speed up mapping landslides around the state, Madin said, but there is the question of funding.
To completely map the state would cost $1 million to $2 million and then to identify and monitor the most dangerous places could cost about $1 million a year, Madin said. For now, that’s not in the agency’s budget.
The U.S. Geological Survey has a national landslide hazard map, but it was made in 1982, according to the USGS website . Again, money becomes an issue.
“We do as much as we can given the amount of funding that Congress gives us,” said Leslie Gordan, spokeswoman for the USGS.
Madin said he is set to have a conference call Friday with USGS officials and his counterparts from other state geological agencies around the country. The conversation will be about mapping landslides and finding funding for the work.
A hazard map only shows part of the situation though, said Bill Burns, an engineering geologist with the Oregon Department of Geology and Mineral Industries. Overlaying a map with roads, homes and buildings would give a true picture of what is at risk.
“The real question is, do we have high hazard where we have people living,” he said.
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