The Cerro Grande fire began as a controlled burn in the Bandelier National Monument,in New Mexico, on May 4, 2000. The wildfire quickly spread to the north, engulfing 19,300 hectares (ha) (47,690 acres) of timberland (primarily), as well as portions of the town of Los Alamos and Los Alamos National Laboratory. Thirty-four percent of the burned area was classified by the Burned Area Emergency Rehabilitation Team as high-burn severity, which resulted in the formation of water-repellent soils, as well as concomitant reduction of the water-retaining properties of previously vegetated slopes. The potential for near-term mass-wasting activity was evaluated through analysis of: (1) topographic, biologic, and geologic factors; (2) location and extent of water repellant soils; and (3) historic evidence of landslide activity in the immediate area. This analysis indicates that danger from geologic hazards in the project area (caused by the effects of the Cerro Grande fire) is low. To a large extent however, the occurrence of landslides, debris flows, and floods depends on the location, duration, and amount of precipitation. These critical factors cannot be predicted. The burn mosaic and locations of hydrophobic soils indicate that minor flooding might occur in streams from Pajarito Canyon in the south to Guaje Canyon in the north. White Rock Canyon has experienced multiple landslide episodes on a large scale. Although this has been the most active mass-wasting site, it is not anticipated that discharge from the streams from the burn area would be of sufficient volume to cause problems, other than minor flooding in the canyon.
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