Glaciers and natural hazards of hazard. Glacier floods are of particular concern in view
of the rapidly retreating glaciers and the corresponding
Changes in glaciers may well lead to hazardous condi- formation and growth of numerous glacier lakes
30,32–34
.
tions, particularly in the form of avalanches and floods,
and thus have dramatic impacts on human populations In terms of hazard, ice and rock avalanches may be
and activities located in glacierized mountain regions. roughly grouped by volume. Avalanches with volumes
The majority of glacier hazards affect only a limited area smaller than 1 million m
3
are mostly of concern to dense-
– often only a few square kilometres – and mostly pose ly populated and developed mountain regions such as the
a danger to densely populated mountain regions such European Alps
41–43
. Avalanches with a volume of 1 to 100
as the European Alps. In some cases, however, glacier million m
3
or even more have usually more far reaching
hazards have far-reaching effects over tens or even hun- effects and the potential to completely devastate mountain
dreds of kilometres and thus also affect less densely pop- valleys. The most recent such disaster occurred in 2002
ulated and developed mountain regions. The long-term in the Caucasus with a 100 million m
3
ice-rock avalanche
average annual economic loss from glacier disasters or that extended more than 30 km downstream and killed
related mitigations costs are estimated to be in the order more than 100 people (see box on the 2002 Caucasus ice-
of several hundred million US dollars
28
. The largest dis- rock avalanche and its implications). These types of mass
asters have killed more than 20 000 people, for instance movements and the relationship between their magnitude
the Huascarán rock-ice avalanches in Peru in 1970 (see and their frequency have recently have become more and
box on deadly ice avalanches of Glaciar 511 in the Cor- more important in research because of concerns that they
dillera Blanca in Part 2 of this chapter), or the Nevado may become more frequent with continuing atmospheric
del Ruiz lahars (rapidly flowing volcanic debris flows) in warming, permafrost degradation and related destabiliza-
Colombia in 1985. tion of steep glaciers and rock walls
44
.
A systematic assessment of hazards can only be achieved Debris flows from periglacial areas have frequently caused
by identifying the physical processes involved. Generally damage to life and property in mountain areas
48
. Uncon-
speaking, the most important types of hazards are as solidated sediments, uncovered by glacier retreat during
follows: glacier floods, hazardous processes associated the recent decades, and degradation of stabilizing perma-
with glacier advance or retreat, ice and rock avalanches, frost in debris slopes are the main sources of the largest
periglacial debris flows, and ice–volcano interactions
29,30
. debris flows observed in the European Alps
31,49,50
.
Particularly severe disasters have often resulted from a
combination of these processes or chain reactions
13,31
. Ice-capped volcanoes pose particularly severe hazards
because large mass movements (avalanches, lahars)
Glacier lake outburst floods represent the largest and may result from the interactions between material that
most extensive glacial hazard, that is, the hazard with the erupts from the volcanoes with ice and snow
51,52
. Alaska,
highest potential for disaster and damage (up to 100 mil- the Cascades and the Andes are among the regions most
lion m
3
break-out volume and up to 10 000 m
3
per second affected by hazards posed by the interaction between
runoff). The Himalayas, Tien Shan and the Pamirs (see volcanoes and glaciers
53,54
.
box on glacier lake outburst floods and glacier surges in
Central Asia), the Andes, but also the European Alps are Chain reactions and interactions between the aforemen-
among those regions most severely affected by this type tioned processes play a crucial role in determining the
124 GLOBAL OUTLOOK FOR ICE AND SNOW