When landslides become a laboratory

The Portland area has just slogged through one of its rainiest Januaries on record.

In western Oregon, Portland averages approximately 40 to 45 inches of rainfall per year between October and May.

Almost 10 inches of rain fell last month, making it Portland’s wettest January since 11.81 inches fell in 1970, according to the National Weather Service. January’s normal rainfall is 5.07 inches.

Heavy rain comes with its own set of hazards, including fender-benders, plugged storm drains, high water, downed power lines, flooded basements and lots of mud.

For Portland State’s geology department, their long history of landslide study turned Portland’s recent sogginess into a giant, living laboratory.

“When you have that much rain, you’re bound to start having landslides,” said Scott Burns, a professor in the department of geology. “All you need is a slope, the right kind of soil and a bunch of water dumped on top of it.”

Slides caused trouble all over the greater Portland area in late January and early February. Portland State’s geology department maintains an active presence in all types of geology fieldwork, including landslides. In a particularly visible and ongoing project, geology students at PSU have studied Oregon City’s Newell Canyon for 14 years, investigating its streams, wetlands, geology and soils.

“In 1992 we did a landslide study of the whole canyon,” Burns said. “We found that it was an extremely unstable area. We mapped the old slides, produced a report and presented it to the City Council in January of 1993.”

At that time, developers planned to build a series of housing developments on the Newell Canyon site, right on top of a series of huge old landslides.

“If a hill has moved once, it’s going to move again,” Burns said. “We recommended that they either cut back on the size of the development or not build at all.”

One of the diciest sites was that of the proposed Newell Creek Village Apartments. Ignoring the landslide date, developers continued to argue in favor of safe construction, while Burns and students argued back that the land sat atop the best example of slide topography in the canyon – a high hazard area.

In the end, while the planned 250 units were scaled back to 125, the complex was built.

“This year, it started to move,” Burns said. “For us it’s a great example of a worthwhile, credible student project. We got the data, we presented it to the town and they only partially took our word. Now they’re regretting it.”

The last patch of soil-saturated ground between the complex’s buildings and the canyon’s slopes slid downhill over the last two weeks. The buildings’ foundations were exposed, and residents were evacuated.

In another example of hands-on geology, Burns and his students were in action during the peak floods of Feb. 6 ?” 10, 1996. All of northwest Oregon’s rivers flooded, and landslides were everywhere.

“We mapped 705 slides that winter,” Burns explained. “In a normal year, we usually have four or five. In a really wet year, we might do 40 or 50.”

During the soggy 1996 winter, Burns’ students mapped and characterized the relation between the local geology, the types of landslide and where the slides occurred. The work generated an extensive data collection, which became one of the biggest landslide databases in the United States.

“The work was done by three grad students,” Burns said. “Today, one of that team is the head of landslide research for the Oregon Department of Forestry, one studies landslides for the state geological service and the third is a geology consultant here in town. We’ve got many students like these, working successfully in the field.”

According to Burns, today’s job market is rich for environmental and field-type geologists, and our current rain-soaked winter has provided a host of opportunities for field study.

“We’ve had almost 11 inches of rain in the past 30 days,” said Burns. “With that, we’re having lots of landslides. Portland has plenty of steep slopes and weak soils, just primed for slides. All you have to do is add water, and we’ve had plenty of that.”

Burns currently has several geology students out around the Portland area, studying actual slides and areas at risk for slides.

One of the high-risk sites is at the University of Portland. A fire last year burned and denuded a steep slope just below the school.

“The whole slope is ready to go,” Burns said.

His students are also studying a very large, secret slide on private property in Portland’s West Hills. Burns estimates the landslide at about 1,000 feet long and some 200 feet wide on its top end.

Burns’ students are monitoring the slide and are also intervening, helping the homeowners, “so that the slide doesn’t leave the property,” Burns said. Long-term modifications to the site may involve the building of check dams and the use of evergreen plantings to stabilize the slope.

The geology department is also working on a joint project with the U.S. Geological Service and the Oregon Department of Geology and Mineral Industries (DOGAMI).

“We’re combining efforts on a big project in the West Hills,” Burns said. “We’re trying to model landslides – to tell where and when they’ll occur.”

Burns and his students just finished installing a group of soil moisture gauges, and in the past week took their first measurements.

“We’ve essentially got a weather station set up in the forest,” Burns said. “We can measure and record precipitation, humidity, air temperature and soil moisture content at three different depths. We’ll eventually have a working model of what type of precipitation will create landslides.”

This is the first of four similar stations, each of which will provide data for creating models and predicting landslides. Students return to the site weekly to download data. Eventually, electronics will be added to allow satellite uplink and automated data retrieval.

“In another part of the project, we’re taking our own landslide database and putting it into a GIS [Geography Information Systems] program to create maps of landslides,” Burns said.

“We’re using a new type of imagery that lets us see right through the forest,” he continued. “It’s called LIDAR – Light Detection and Ranging – and it uses laser infrared. We’ve got students using it to map old landslides. We’ll eventually have a map of where landslides have occurred in the past, and with that we’ll be able to create a predictive model.”

Portland and surrounding cities would find this type of data immensely useful for new constructions and building permits.

“It’s really gratifying to see these students doing work that’s interesting and important,” he said. “They’re making a difference.”

Portland State’s landslide studies began in the 1950s, Burns said. The then-young geology department was called out to monitor a slide site next to the present-day Oregon zoo.

“The highway department had cut the toe off the hill that the zoo was built on,” Burns said. “The whole hill started to move.”

An archival sepia-tone photograph posted in the geology department shows three grinning student geologists standing next to a sign saying, “zoo crossing.”

“That was the joke,” Burns said. “The whole zoo was trying to cross the road, so these guys put up the sign.”