Natural Hazards in southern British Columbia

The interaction of strong north-south geomorphic obstructions and a low population density dominate the risk assessment for British Columbia. The north-south mountain ranges and valleys place severe limitations on where transportation and other infrastructure may be built. The limited economic routes are highly vulnerable to landslides and avalanches, requiring significant and ongoing mitigation of the risk. The major population centres are mostly along the southern border, exposed to volcanic eruption hazards from Washington, or along the coast, subject to an active subduction zone. These considerations dominate the hazard management within the province.

Physical Context

British Columbia is formed by northwest-southeast strips of terranes accreted onto the continental plate. The continental divide is roughly along the provincial border with Alberta. The western region is subject to active tectonic processes as the Juan de Fuca and Explorer Plates subduct under the North American Plate. Far western and eastern British Columbia are mountain ranges, while the interior is comprised of a series of plateaus and low mountain ranges.

The climate of British Columbia typically mild, with coastal temperatures typically ranging ±10 °C , and even extreme temperatures rarely broaching ± 30°C. The mountain ranges experience heavy precipitation (> 1 m/yr), while the interior is semiarid (≈0.3 m/yr).

Implications for Hazard Management

The extreme topography hampers wireless communication, with limited cell coverage outside of urban centers, and sometimes even limited access to satellite communication due to the tall peaks and narrow valleys. The already limited telecommunications are extremely vulnerable, making planning for communication during emergency response a challenge.

The disaster history of British Columbia suggests the the dominant concerns deal with earthquakes and mass movements, with awareness of the impact of floods, severe weather, nearby volcanic eruptions, and both local and distant-sourced tsunami

Social Context

Canada is a young country, with a growing population expanding primarily in geographically limited urban areas. The national average population density is 3.5 people per km² dropping to fewer than 1 person per km² within Britsh Columbia, with most of the population concentrated along the southern border in high-density settlements. This heterogeneous population density results in a far different approach to managing natural hazards than the more densely populated Europe where unpopulated regions are far more rare.

Implications for Hazard Management

As Canada is such a young country, written record of hazards is shorter than common in Europe, with less than 200 years of formal record-keeping in British Columbia. As high-intensity events are relatively infrequent, few are recorded. Additionally, as the modern low population density is still dramatically higher than for most of the province’s history, many events which occurred historically would be significantly more damaging were they to occur today. Many of the province’s largest-volume landslides resulted in no or few deaths and injuries, due to luck and low population densities.

The low population density, clustering along the southern border, and strong geomorphic north-south obstructions conspire to limit transportation and communication corridors. The corridors are often multi-purpose (with rail, roads, telecommunications, and pipelines in close proximity), and extremely vulnerable to hazards.

Current Hazard Management

The first stage of hazard management is to identify the hazards through inventories and assessments When a hazard is identified, models are used to establish the likely extent, intensity, and frequency of events to create a hazard map. The hazard map is used in combination with an assessment of the vulnerability of people or objects exposed to the hazard to determine the risk. Actions to change the established risk are to do nothing, to avoid the hazard, to mitigate through education, to monitor and forecast changes in the hazard, and to mitigate or eliminate the hazard through engineered solutions. The action depends on the risk, the physical parameters of the hazard and mitigation techniques, and the projected economic and social cost.

References

Environment Canada (2000). Canadian Climate Normals 1971-2000.
Mathews, B., & Monger, J. (2005). Roadside Geology of Southern British Columbia. Mountain Press Publishing Company.
McKinnon, M. (2010). Parameter Selection for Modelling Catastrophic Landslides. Master’s thesis, University of British Columbia.
Public Safety Canada (2007). Natural Hazards of Canada.
Statistics Canada (2006). Census.
Transportation Safety Board of Canada (1997). Derailment Canadian National Train No. Q-102-51-26. Railway Occurrence Report R97V0063. 1997.

Further Reading

Field report for the geoNatHaz 2010 Canadian field school covering approximately 2,600 km through southern British Columbia and southwestern Alberta.

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