magnitude and frequency of glacier-related hazards. As The second important change in glacier-related risks
one example, outbursts of naturally or artificially dammed concerns the increasing economic development in
mountain lakes were caused by impact waves from rock most mountain regions. Human activity is increasing-
and ice avalanches and this led to failure of the dams
55
. ly encroaching upon areas prone to natural hazards.
Such potential process interactions have to be assessed Related problems affect both developed and develop-
carefully in order to predict related consequences. ing countries. The latter (such as in Central Asia, the
Himalayas or the Andes), however, often lack resources
Two present global developments and their regional ex- for adequate hazard mitigation policies and measures.
pressions will strongly affect the potential impact of cur- Cost-efficient, sound and robust methods are there-
rent and possible future glacier hazards: climate change fore needed to regularly monitor the rapid environ-
and socio-economic development. First, atmospheric ment and land-use changes in high mountains and to
warming has an increasingly dramatic effect on moun- identify the most vulnerable areas. This is equally im-
tain glaciers
1
, and strongly influences the development portant for developed countries in the European Alps.
of related hazards. For example, potentially unstable Expensive protective structures had to be built in the
glacial lakes often form in glacier forefields dammed by past to reduce the risk. Public funds increasingly strug-
frontal moraines which were left behind by retreating gle to keep pace with – and to ensure sufficient protec-
glaciers. Steep slopes of unconsolidated debris are a po- tion from – the rapid environmental changes and their
tential source for debris flows when they are no longer consequences in mountain areas. Integrating climate
covered by glacier ice or cemented by ground ice. Fresh change effects and robust process models into risk
ice break-off zones may evolve in new places from glacier studies will help ensure that politics and planning can
retreat, while existing danger zones may cease to be ac- adapt to environmental conditions that change with in-
tive. Atmospheric warming also affects permafrost thick- creasingly high rates.
ness and distribution. The thickness of the active layer
(that is, the layer above the permanently frozen ground
that thaws during the summer) may increase, and the Glaciers, landscapes and the water cycle
magnitude and frequency of rockfalls may increase or
evolve at locations where such events were historically Landscapes around many high-mountain regions
unknown. Lateral rockwalls can be destabilized by gla- but also in vast lowlands were moulded and sculpt-
cier retreat as a result of the stress changes induced. In ed by large ice bodies during the most recent part of
general, climate change is expected to bring about a shift Earth’s history – the Ice Ages – over the last few mil-
of the cryospheric hazard zones. It is difficult, however, lion years
57,58
. The detection, in the first half of the
to ascertain whether the frequency and/or magnitude of 19th century, of corresponding traces from glacier ero-
events have actually increased already as a consequence sion and of erratic boulders far from mountain chains
of recent warming trends. Nevertheless, events with no led to the formulation of the Ice Age theory by Louis
historical precedence do already occur and must also be Agassiz and colleagues
59
. It was soon understood that
faced in the future
29,56
. large ice sheets had formed over North America and
CHAPTER 6B GLACIERS AND ICE CAPS 127