The Role of Geomorphology in the Identification and Evaluation of Natural Hazards

Abstract

Air photograph interpretation and detailed field investigations have been used to identify and evaluate a wide variety of natural hazards in Shakwak Valley, part of the main transportation corridor linking Alaska and western Canada. Potential natural hazards to communities, roads, and proposed major developments such as the Alaska Highway gas pipeline include (a) seismic shaking and surface rupture associated with active faults; (b) rockslides, rockfalls, slumps, and complex landslides; (c) active-layer detachment flows; (d) debris flows and debris torrents; (e) floods triggered by heavy rainfall and snowmelt; (f) jokulhlaups; (g) inundation of Haines Junction by a large glacier-dammed lake (Lake Alsek); (h) explosive volcanism; and (i) permafrost degradation. An evaluation of each of these hazards for the purpose of land use planning has been made first by determining locations of potential hazard areas relative to existing development in Shakwak Valley, and then by estimating the probability of occurrence and the likely areal extent of damage for destructive events of various magnitudes. Probabilities of the various hazards in Shakwak Valley are based on meager historical data and on radiocarbon dates on terrain features and sedimentary deposits produced by past “catastrophic” events. The following conclusions can be drawn from estimates of the probability of occurrence and probable economic impact of natural hazards in Shakwak Valley. The greatest short- to intermediate-term (10 to 100 years) hazards to life and property are floods, debris torrents, and earthquakes. Inundation of Haines Junction by Lake Alsek and catastrophic jokulhlaups elsewhere in the valley, although potentially extremely destructive, are unlikely to occur under present climatic and glacier balance conditions. Finally, large landslides and tephra falls in Shakwak Valley not only have lower probabilities than other hazards, but also would probably cause less damage.