Landslide initiation locations in Nicaragua

Aerial photographs taken between December 4 and December 19, 1998 under the Open Skies program of the Defense Threat Reduction Agency were used to map the intiation locations of the landslides shown on the maps. The aerial photographs are at 1:60,000-scale, and 1:30,000-scale for portions of the Matagalpa and Jinotega/San Rafael del Norte study areas. Digital Raster Graphic (DRG) scanned images of 1:50,000-scale quadrangles projected to Transverse Mercator were used as base maps for the mapping. We mapped landslides by first identifying them on the aerial photographs using a mirror stereoscope and then manually plotting each landslide and its affected area by inspection onto the base maps. In some cases, the base maps were enlarged to 1:25,000-scale to facilitate mapping.

Field reconnaissance from April 25 through May 6, 2000 resulted in limited verification of the landslide and related effects mapping. Because of the large areal extent of the study areas and difficulties of access, we visited only a few, small areas. We observed as few as 5% of the landslides in some study areas and as many as 40% of the landslides in others. During this reconnaissance, we mapped the locations and extents of some landslides outside the coverage of the aerial photography. This mapping represents only features that we observed, and is not representative of all the landslide activity in the area.

Following field verification, a point representing the initiation location of each landslide was digitized. This point was located as the highest elevation point within the landslide polygon.