In 1959, a rock spur became detached from the headwall of a cirque near Pandemonium Creek in the southern Coast Mountains of British Columbia. Approximately 5,000,000 cu m of blocky, gneissic quartz diorite debris travelled 9.0 km along a highly irregular path, descending a vertical distance of 2 km to the valley of South Atnarko River. The high mobility of the rock avalanche is manifested by superelevation in valley bends, two run-ups, and two right-angle changes in flow direction. This mobility is due, in part, to (1) peculiarities in the path of the landslide (lateral moraines, for example, funnelled and accelerated the debris) and (2) travel over a glacier below the detachment zone. Although most of the debris came to rest on the upper part of a fan at the mouth of Pandemonium Creek, one lobe traversed the fan and entered Knot Lakes, where it generated displacement waves that destroyed trees along the shore. Run-up and superelevation data indicate that the debris was moving between 81 and 100 m/s as it entered the run-up zone at Pandemonium Creek and 21-38 m/s in Pandemonium valley to the east. These velocities were analysed by applying the dynamic model of H.J. Korner (Rock Mechanics, 1976, 8: 225-256) to the path of the landslide. The analysis suggests that the rock avalanche had two phases: a very rapid initial phase from detachment to the beginning of the run-up, and, following sudden energy losses at the run-up, a second phase involving much lower velocities. The Pandemonium Creek landslide is similar in many respects to much larger, highly mobile rock avalanches in other parts of the world, for example, Huascaran (Peru) and Little Tahoma Peak (Washington, U.S.A.). Although much less common than rockfalls and debris flows, rock avalanches are capable of far greater damage. This is a consequence of their size and the fact that they travel great distances at high velocities. The potential exists for other highly mobile landslides of the Pandeminium Creek type in the mountains of western Canada, highlighting the need for caution in the future development of this region.

  • Corporate Authors:

    National Research Council of Canada

    Research Journals
    Ottawa, Ontario K1A 0R6,   Canada 
  • Authors:
    • EVANS, S G
    • HUNGR, O
  • Publication Date: 1989-8

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 427-446
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00488244
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 30 1989 12:00AM