United States Army Corps of Engineers, Hydrological, Coastal, and River Engineering Section
Date of Award
Master of Environmental Management (MEM)
Environmental Science and Management
Mount Saint Helens (Wash) -- Eruption (1980), Volcanic eruptions -- Washington (State) -- Mount Saint Helens -- Measurement
The May 18, 1980 eruption of Mount St. Helens created a massive amount of sediment and debris, thought to be as much as 5.5 billion cubic yards. This sediment causes infill of river stretches and collects along levees protecting southwest Washington State. The sediment must be removed to ensure these areas do not flood. The US Army Corps of Engineers (USACOE) is tasked with flood protection for southwest Washington State and the levees protecting the cities of Castle Rock, Lexington, Kelso, and Longview. The Sediment Retention Dam, opened in 1989 is able to filter out larger particulate but fine grain sediment remains in the water column and is transported further down the river. In order to calculate how much sediment remains to be removed Portland State University’s Environmental Sciences and Management program and the USACOE formed a partnership and generated Digital Elevation Models (DEM) from topographic maps made by the United States Geological Survey (USGS). This was accomplished by taking 600 dots per inch (dpi) scanned images of the eruption path, geographically rectifying them in ESRI’s ArcMap software environment, and running Iterative Self-Organizing Data Analysis Technique (ISODATA) Unsupervised Classification utilizing ERDAS Imagine 9.3 software. After the contour lines were extracted from the images we cleaned up the lines in a raster environment, converted the raster to vector lines, and entered elevations.
From these contour lines we created the DEM and calculated the volume difference between the pre-eruption 15 minute USGS maps and the 7.5 minute post-eruption quad maps. The volume difference was 7,870,546,345 m3 for Mount St. Helens quads, - 4,335,917,517 m3 for Spirit Lake quads, -220,149,557 m3 for Goat Mtn. in Cougar quads, -3,155,437,891 m3 for Elk Rock quads, and 734,102,545 m3 for Hoffstadt Mtn. in Elk Rock pre quad. These figures indicated a large generation of sediment and debris on the slope north of Mount St. Helens, sediment deposition in the Hoffstadt Mtn. river reach, and erosion in all other areas. The USACOE will use my raw data contour elevation lines to create their own DEMs incorporating stream locations to further refine the data. From this data they hope to extrapolate how much sediment is left and where the sediment deposits are likely to erode from in the future.
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Wickham, Dâvid Nuñez, "Calculating the Volume of the May 18, 1980 Eruption of Mount St. Helens" (2009). Environmental Science and Management Professional Master's Project Reports. 9.