Digital elevation models of Mount St. Helens crater and upper North Fork Toutle River basin, based on 1987 and 1999 airborne photogrammetry surveys Digital elevation models of Mount St. Helens crater and upper North Fork Toutle River basin, based on 1987 and 1999 airborne photogrammetry surveys Digital elevation models of Mount St. Helens crater and upper North Fork Toutle River basin, based on 1987 and 1999 airborne photogrammetry surveys

The lateral blast, debris avalanche, and lahars of the May 18th, 1980, eruption of Mount St. Helens, Washington, dramatically altered the surrounding landscape. Lava domes were extruded during the subsequent eruptive periods of 1980-1986 and 2004-2008. Nearly four decades after the emplacement of the 1980 debris avalanche, high sediment production persists in the North Fork Toutle River basin, which drains the northern flank of the volcano. This high sediment production poses a risk of flooding to downstream communities along the Toutle and Cowlitz Rivers and of clogging the shipping channel of the Columbia River. Consequently, U.S. Army Corps of Engineers (USACE), under the direction of Congress, built a sediment retention structure on the North Fork Toutle River in 1989 to maintain an authorized level of flood protection. During 1987 and 1999, WH Pacific, under contract to USACE, facilitated airborne photogrammetry surveys of Mount St. Helens crater and upper North Fork Toutle River basin. Digital softcopy photogrammetry techniques were used to produce a contour map, breaklines, and masspoints. The U.S. Geological Survey (USGS) used these data to produce a digital elevation model (DEM) of the survey areas. This USGS data release contains digital elevation data as a 10- and 30-foot resolution raster datasets (dem_1987.tif and dem_1999.tif). These DEMs can be used to develop sediment budgets and models of sediment erosion, transport, and deposition.