Seattle Area, Washington

Science Center Objects

Recent ConditionsNational Weather Service:

Bluff location:

Data is updated every 60 minutes. Updates may be interrupted occasionally by instrument, computer, or network malfunctions.

Monitoring at this site is for researching rainfall thresholds for forecasting landslide potential. Shallow landslides are common on coastal bluffs overlooking Puget Sound. Hundreds of landslides occurred on the bluffs in late December 1996 and early January 1997 as heavy rainfall accompanied by abrupt warming caused rapid melting of recent heavy snow. Smaller numbers of landslides occur every few years during extended rainy periods and intense storms.

 

Cumulative Precipitation Threshold

Graph of the cumulative precipitation threshold for Seattle Area

The Cumulative Precipitation Threshold is (3-day Precipitation)=3.5 - 0.67*(15-day Precipitation).

(Public domain.)

The cumulative precipitation threshold for the occurrence of landslides in the Seattle area is based on an analysis of historical landslide and precipitation data from the period 1933 - 1997. The threshold was visually identified after plotting antecedent 3-day and prior 15-day cumulative precipitation amounts associated with landslides that were part of events with 3 or more landslides in a 3-day period. Between 3.5 and 5.2 inches total precipitation during any 18-day period (last 3 days plus the previous 15 days) are required to exceed the cumulative threshold. It is interpreted as a lower-bound threshold below which the specified level of landslide activity does not occur or occurs only rarely. Recent analysis has shown that the probability of landslides occurring on a day when the cumulative threshold has been exceeded is roughly 10%. See USGS Open-File Report 00-469USGS Open-File Report 03-463, and USGS Open-File Report 06-1064 for details concerning the identification of the threshold and its performance.

 

 

Rainfall Intensity-Duration Threshold

Graph of the rainfall intensity-duration threshold in the Seattle Area.

The Intensity-Duration Threshold is Intensity=3.257(Duration)**-1.13.

(Public domain.)

The rainfall intensity-duration threshold for the occurrence of landslides in the Seattle area is also based on an analysis of historical landslide and precipitation data from the period 1933 - 1997. This threshold was developed to identify conditions when abundant landslides are likely. Recent analysis has shown that the probability of landslides occurring on a day when the intensity-duration threshold has been exceeded is between 30% and 70%, depending on antecedent soil wetness and size of the area affected by threshold exceeding rainfall. See USGS Open-File Report 06-1064 for details concerning the identification of the threshold and its performance. USGS Fact Sheet 2007-3005 also has more information about the rainfall thresholds and their application to forecasting landslides.

 

 

 

Landslide starting on the side of a cliff in the Seattle Area

Photograph showing head of a landslide in 1997 that eventually destroyed several homes near the south end of Perkins Lane in Seattle, Washington.

(Public domain.)

Landslide came across a road in Seattle, into a house on the side of a cliff

Photograph showing a house that was damaged by a 1997 landslide along Perkins Lane in Seattle, Washington.

(Public domain.)

 

landslide on the side of a cliff with a house at the top of the cliff, looking up at the house

Photograph showing the scar left by a landslide on a hillside above the Burlington Northern Santa Fe Railway in Everett, Washington.

(Public domain.)