People in the Mountains - Mountain Geography: Physical and Human Dimensions - page 526

the former common among longtime mountain dwellers and the latter now more com-
mon in highly developed and regulated jurisdictions in Europe and North America. Mit-
igation includes: strengthening of slopes using retaining walls, bolts, pylons, terracing,
coatings, and vegetation; catching or diverting rockfalls and debris and mudflows us-
ing nets, walls, dikes, and sheds; draining water from slope using pipes, tiles, and di-
versions; strengthening buildings, bridges, and support structures against impacts; and
forecasting and warnings to alert people to danger, close facilities, roads, and so on,
and initiate evacuations if necessary.
As discussed in Chapter 6, soil erosion is a more subtle but, in the long term, very
damaging process in mountain environments. It results primarily from water runoff on
soils and is especially prevalent in areas of soil exposed for agriculture and construc-
tion.
Snow Avalanches
Snow avalanches, the sudden and rapid downslope movement of masses of snow, are
the most widespread and common hazardous processes in high mountains. Millions oc-
cur globally every year, but relatively few pose a risk because they occur in remote
locations. Nonetheless, they have been and remain a very significant hazard in popu-
lated and heavily used locations, as discussed in Chapter 4. The growth of snow-based
tourism and recreation has dramatically elevated risk (McClung and Schaerer 2004). In
addition to posing a hazard, snow avalanches transport sediment, influence vegetation,
and redistribute water, soil, and wood in ways that are both harmful and beneficial to
mountain people. For example, in the snow-covered parts of the northwest Himalaya in
northern Pakistan, Kashmir, and Himachal Pradesh, avalanche-transported snow, sedi-
ment, organic material, and wood contribute to agriculturally productive fan deposits
and to the local firewood supply (De Scally and Gardner 1994). On balance, however,
avalanches are seen primarily as a hazard.
Advanced scientific understanding of snow avalanches has aided the effective man-
agement of the hazard, especially since the 1950s, when the combination of the rapid
and widespread expansion of recreational skiing in Europe and North America, and very
serious avalanche disasters in Europe during the 1950-51 winter coalesced to a crisis
(Fraser 1966; McClung and Schaerer 2004). Previously, mountain people had reason-
ably effective traditional and local knowledge of avalanches that helped them to man-
age risk by winter evacuations, avoidance of dangerous locations for, and modifications
of, permanent dwellings, maintaining protective forests, and forgoing travel, during
high hazard episodes (Fig. 10.20). As discussed in Chapter 4, a better understanding
of the interactions between topography, weather, and snow conditions, the three prin-
cipal ingredients of avalanche conditions, are enabling more effective management of
the hazard and the risk. The mitigating measures include: identification of avalanche
slopes and event frequency and magnitude to produce effective hazard maps; using haz-
ard maps to regulate the location of activities and structures; monitoring weather and
snowpack conditions to forecast avalanche hazards; using forecasts to pre-release ava-
lanches with explosives in selected locations; regulating highway, rail, and recreation-
al traffic and activity during high hazard conditions; issuing public information bullet-
ins indicating hazard levels and using public education to upgrade general knowledge