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A new lidar-based landslide inventory maps show more than 7,000 past landslides - 10 times as many as research teams mapped after 1996-97 storms.

PAMPLIN MEDIA GROUP FILE PHOTO - A January 2006 landslide damaged property on Southwest Cardinell Street, crushing two cars beneath the rubble. A new state study is drawing lines across Multnomah County where landslides could happen, and where residents and buildings are most at risk.

The study by Oregon's Department of Geology and Mineral Industries included the cities of Portland, Gresham, Troutdale, Fairview and Wood Village, and shows areas where working to reduce landslide risk could make a difference. About 37,000 people live, and about $8.7 billion in buildings and land value are in areas with a high probability of landslides, according to the study. About 6,700 of those people and $1.65 billion of building and land value, sit atop property affected by past landslides.

"Even a few inches of movement during landslides can cause serious damage," says Bill Burns, an agency engineering geologist and the study's lead author. "Thousands of landslides have occurred in Multnomah County since the 1970s, and are continuing to happen every year."

(Image is Clickable Link) COURTESY PHOTO - An interactive map shows past landslides across the Portland area.The study used lidar (a pulsed-laser measuring tool), which offers a detailed look at the earth's surface, to help identify where landslides occurred in the past. The study's new lidar-based landslide inventory maps show more than 7,000 past landslides — 10 times as many as research teams mapped after 1996-97 storms.

The study also used new geology data to create landslide susceptibility maps, which show areas where landslides are more likely to occur in the future.

"Overall, the study shows significant landslide risks in some areas of Multnomah County," Burns says. "It's important to continue working to reduce our landslide risks, and there are steps we can all take to do that."

Find the study and interactive maps at www.OregonGeology.org.

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