Introduction
The southern Coast Mountains were largely remote and undeveloped until about 50 years ago. Beginning in the 1950s, and accelerating in recent years, parts of this region have been opened to resource development, urbanization, and recreation. A highway extends north through the Coast Mountains into the British Columbia interior. It connects Vancouver to Whistler, North America’s premiere ski resort, and skirts the west flank of Mount Garibaldi.
As development has proceeded, conflicts have arisen over land use. The conflicts have centred on whether or not landslides (particular very large events resulting from the collapse of volcanic edifices) are a threat to public safety. We will examine two cases, and assess whether government intervention was warranted in either case.
Rubble Creek
In 1972 the BC Ministry of Transportation and Highways, which is responsible for land-use regulations in unincorporated areas of the province, approved the first stage of a subdivision for 126 housing lots on a fan that had been overrun by a large landslide near Mount Garibaldi in 1855-1856. However, having been alerted to the potential landslide hazard on the fan, the Ministry refused to approve the second stage of development on public safety grounds. This decision was appealed in court by the developer, but the Supreme Court of BC dismissed the appeal in 1973. Chief Justice Thomas Berger stated that "there is sufficient possibility of a catastrophic slide during the life of the community" to disallow development of the site. The judgment established an important precedent relating to planning and development of permanent settlements in the mountainous areas of western Canada.
You are presented with a topographic map (1:50 000), a map of the area affected by the 1855-56 avalanche, and a "fact sheet".
Questions to consider:
(a) What is a 'rock avalanche'?
(b) Why is "The Barrier" unstable?
(c) How confined is the avalanche path?
(d) Was Garibaldi in the run-out zone in 1855-56?
(e) Was the Ministry's decision justified?
(f) How would you define "the life of the community" in this context?
(g) What other facilities are at risk from this source?
Cheekye Fan
The community of Brackendale, a suburb of Squamish, is located on the lower part of a large debris flow fan (Cheekye fan). As population in this area has increased, pressure has mounted to develop the upper parts of the fan near its apex. However, concern that this area might by overrun by a large debris flow originating at the head of Cheekye River on the precipitous west flank of Mount Garibaldi led the British Columbia Ministry of Transportation and Highways to contract a geological and geotechnical study of the area by Thurber Engineering and Golder Associates. The study involved an examination of the geomorphology of the fan, the stratigraphy of the uppermost fan sediments, and modeling of hypothetical debris flows. Many debris flows were identified in the sediments forming the fan, although few were adequately dated. On the basis of this study, the Ministry of Transportation and Highways established zones in which development would be allowed, restricted, or prohibited.
You are presented with a topographic map (1:50 000), a map of the Cheekye Fan zones, and a "fact sheet".
Questions to consider:
(a) Why does the western flank of Mt. Garibaldi generate debris flows, rather than rock avalanches?
(b) Why is this source area unstable?
(c) How confined is the debris flow path?
(d) Is Brackendale in the run-out zone of large debris flows?
(e) Was the Ministry's decision to restrict development justified?
(f) What other facilities are at risk on the fan?
|
|