FIRE-RELATED DEBRIS FLOWS ON STORM KING MOUNTAIN, GLENWOOD SPRINGS, COLORADO

(S.H. Cannon, P.S. Powers, and W.Z. Savage; U.S. Geological Survey, Denver Federal Center, Mail Stop 966, Denver, Colorado)

The South Canyon Fire of July 1994 burned 800 ha of vegetation on Storm King Mountain near Glenwood Springs, Colorado, USA. On the night of September 1, 1994, in response to torrential rains, debris flows inundated four places along a 4.8-km length of Interstate Highway 70. Mapping from November 1994 1:8000-scale aerial photographs, along with field observations and measurements, shows that the September rainstorm flushed dry-ravel deposits from the side channels, transported loose, larger material from the main channels, and eroded unconsolidated, burned surficial soil from the hillsides. This material was mobilized into a combination of debris- and hyperconcentrated flows. The flows inundated approximately 14 ha of Interstate Highway 70 with roughly 70,000 m3 of material. Flow velocities from 3 to 9 m/s are calculated, with discharges between 28 and 113 m3/s. Approximately 15% of the loose, unconsolidated soil on the hillsides was removed to a depth of 50 mm by rilling and sheetwash. Although the burned area was seeded in November of 1994, the potential for continuing and destructive debris-flow and landslide activity remains. During the Spring of 1995, a rainfall cell dropped 12.5 mm in 30 min, resulting in up to 3 m of channel incision and debris-flow activity in one drainage in the watershed.


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ed many times in the last forty years, especially on November, 1976 and April, 1985. The Lagariello landslide was particularly remoulded on April, 1978 and 1985.