ENVISIONING AND PREPARING FOR A LANDSLIDE CATASTROPHE IN THE PACIFIC NORTHWEST

In North America, landslides claim an average of about 30 lives each year; the total annual cost of damages exceeds US $1 billion and may be as high as US $3 billion. The Pacific Northwest is a microcosm of landslides in the world’s developed countries, thus we focus on events from this region to illustrate broader issues surrounding risk and vulnerability. Landslides, unlike many other natural hazards, are localized and thus have only local impacts to small areas. Even landslides in urban environments, although typically highly destructive and often fatal, are little more than societal nuisances. In rare instances, however, landslides impact infrastructure on a regional scale, with consequences rivaling those of floods and earthquakes. Examples include blockage of economic and transportation corridors in mountain valleys north and east of Vancouver by rock falls and rockslides due to a large local earthquake; landslide damming of the Columbia or Fraser rivers; and countless debris flows over areas of tens of thousands of square kilometres by a megastorm with a return period of the order of 100 years. Standard engineering mitigation measures are appropriate for most “one-off” landslides, but the rarer, worst-case scenarios, such as those considered in this presentation, cannot be prevented through engineering. Rather, they must be envisioned by emergency managers as possibilities and then explicitly and effectively incorporated into disaster response planning. Only then will we avoid the paralysis that ensues when the “impossible happens”.