Geologic Hazards Overview
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Geologic Hazards Overview 
 

Massive landslide along Magnolia Bluff in Seattle, a hard-hit area during 1996 winter storms. Photo by Hugh ShipmanGeology and Earth Resources Division geologists actively identify, assess, and map geologic hazards using modern geotechnical and geophysical methods. Our hazard maps are critical for land-use and emergency-management planning, disaster response, and building-code amendment. As our population grows, there is increasing pressure to develop in hazardous areas. Delineation of these areas has never been more important.

In response to the Growth Management Act's mandate to use the ‘best available science’, our geologists meet with local governments and townspeople in at-risk communities to educate them about geologic hazards and ensure that these hazards are taken into account in growth-management and disaster planning.

The Division is also among the first responders to disasters, helping staff the State Emergency Operations Center at Camp Murray and later documenting damage in the field.

Landslides

Landslides are a continuing problem along our hillsides, shorelines, and roadways. Just since 1996, landslides have caused hundreds of millions of dollars of damage in Washington.

The Division is a leader in landslide hazard identification, mitigation, and emergency response. Our geologists responded to landslide emergencies in Seattle in 1997, in Olympia and Grand Coulee in 1998, and in Snohomish County in 2002. We have mapped Cowlitz County’s landslide hazard areas to assist with growth-management planning. The county's Aldercrest landslide, which damaged 138 homes, was declared a federal disaster area. Damage to public facilities and private property is estimated in excess of $30 million.

Landslide hazard maps can help prevent this kind of loss to property by showing those areas that are unsafe for building. To this end, additional landslide mapping projects are currently underway or planned for several Washington counties.

Division geologists are also studying large ancient landslides that may record prehistoric earthquakes to help document the recurrence intervals for mega-quakes, which could be devastating to western Washington.

Earthquakes

Geologic evidence suggests that most of Washington is at risk from large earthquakes. In 1700, a mega-quake occurred on the Cascadia subduction zone just off the coast of Washington. The largest quake since European settlement was in a sparsely populated area east of the Cascades in 1872. Puget Lowland earthquakes in 1946, 1949, and 1965 killed 15 people and caused more than $350 million in property damage, and the Nisqually earthquake in 2001 caused more than $2 billion in damage.

The Division produces earthquake hazard maps for at-risk urban areas. These maps show areas where earthquake damage from amplification of earthquake waves or soil liquefaction can be expected to be high. Damage can then be mitigated by either reinforcing structures in these areas or not building there at all.

Five detailed liquefaction maps and one ground-shaking map have been published by the Division to date. Our Olympia map was tested by the Nisqually earthquake and successfully predicted the areas of greatest damage. A federally funded statewide reconnaissance map of ground-shaking and liquefaction susceptibility was completed in 2004 and is available on our website (see Open File Report 2004-20).

Division geologists hold workshops to show cities and counties how to use these maps for land-use and emergency-management planning.

Mount St. Helens from the Pumice Plain, about one mile north of the mountain, on April 16, 1983. Photo by Pat PringleVolcanoes

In the past 12,000 years, Washington’s five active volcanoes have erupted more than 200 times, producing ash, lava, and massive mudflows. The 1980 eruption of Mount St. Helens killed 57 people, blanketed eastern Washington with ash, and caused more than $1 billion in damage.

Mount Rainier is our most dangerous volcano because of the large population close to the mountain. Previous lahars (mudflows) from Mount Rainier inundated Puget Lowland valleys as far as current-day Renton, Tacoma, and Olympia. The Division has mapped and determined the age of many of these events to present a much clearer picture of their frequency and magnitude.

In the past, lahars from Glacier Peak have flowed through the Skagit Valley all the way to La Conner. Recent mapping in Skagit and Whatcom Counties has identified previously unrecognized, young lahars from Glacier Peak that would obliterate small towns such as Darrington and destroy sections of Interstate 5, should they occur today.

The Division collaborates with the U.S. Geological Survey's Cascades Volcano Observatory to produce volcano hazard maps and develop response plans for each volcano. We assist at-risk communities with their land-use, evacuation, and emergency-management plans and hold open meetings in at-risk communities to present the danger and allow citizens to ask questions and voice concerns.

Tsunami hazard signTsunamis

The coast of Washington is at risk from tsunamis of both local and distant origin. These destructive waves are most commonly caused by submarine earthquakes. In 1964, the Washington coast suffered $600,000 damage from a tsunami caused by the great Alaska earthquake in Prince William Sound. Our current technology gives us plenty of warning for tsunamis produced by distant quakes. An earthquake on the Cascadia subduction zone—like the 1700 event or the Indian Ocean earthquake of 2004—could generate a tsunami that would strike our coast with great force within a few tens of minutes.

The Division is on the front line in disseminating information about tsunamis. To date, we have produced five tsunami hazard maps showing projected areas of inundation for much of our outer coast, where more than 40,000 residents and $1.5 billion in property are at risk. We hold informational meetings in coastal communities and help local governments develop evacuation and emergency-management plans.

We also participate in the National Tsunami Hazard Mitigation Program to help improve tsunami warnings, inundation modeling, and dissemination of tsunami research. Our librarian, under a grant from the NTHMP, prepares and publishes TsuInfo Alert, a newsletter that links tsunami scientists, emergency responders, and community planners to the latest tsunami research.

Coal Mine Subsidence

Abandoned coal mines underlie at least 50,000 acres in King, Kittitas, Lewis, Pierce, Skagit, and Whatcom Counties. Some of these mines are near the surface and pose a risk to buildings or other structures from mine collapse. Information about the location and condition of coal mines is necessary to identify hazardous areas. Our extensive coal mine map collection and staff expertise are invaluable in guiding development in these areas. We work with local governments to accurately locate mines and interpret mine maps. We also respond to collapses in urban areas.

The main adit at the Lockwood Pyrite mine, showing acid mine drainage with dissolved metals. Photo by Mac McKayAbandoned Metal Mines

There are more than 3800 abandoned metal mines in Washington. The mines were worked and abandoned before there was a requirement for reclamation and cleanup. Mine hazards include water quality degradation from high concentrations of heavy metals, and physical hazards such as vertical pits, caving shafts, and collapsing underground workings. These hazards have obvious and significant liability problems for land owners, the public, and government. Other states have found that it only takes one accident to create a headline in every newspaper in the state.

We are currently cataloging and investigating these sites for the Inventory of Inactive and Abandoned Mine Lands. The Division was awarded a U.S. Forest Service grant for this work because of our technical expertise and the extensive collection of reports and data about these mines in our library. We are publishing our findings on each mining district as the site investigation work is done.

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 Contacts

Geologic Hazards Group
Geology & Earth Resources Division
Washington State Department of Natural Resources
360-902-1450
Fax 360-902-1785
dnrgeologyhazards@dnr.wa.gov

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