Deadly ice avalanches of Glaciar 511 in the
Tropical glaciers
Cordillera Blanca, Peru
Tropical glaciers are found in the high moun-
Many disasters have been recorded from the glaciers in the Cordillera tains of the Andes in Colombia (Figure 6B.19),
Blanca. The 1962 and 1970 events originating from Glaciar 511 on Venezuela, Equador, Peru and Bolivia, as well
the Nevados Huascarán
142
(Figure 6B.18), the highest peak of which as in the high mountains of East Africa (Figure
is at 6768 m above sea level in the Peruvian Andes, were particularly 6B.20) and Irian Jaya, Indonesia. Around the
severe. On 10 January 1962, an ice avalanche took place with an esti- period 1950–1990 they covered about 2760 km
2
mated starting volume of 10 million m
3
; the avalanche travelled down with about one quarter in the Peruvian Cordill-
16 km and destroyed the city of Ranrahirca, where 4000 people died. era Blanca
143
; this area had shrunk to about 2500
On 31 May 1970, the most catastrophic rock-ice avalanche known in km
2
for the period 2000–2005
144
. The maximum
history was triggered at 3:23 p.m. by a strong earthquake with a mag- extents of tropical glaciers occurred between the
nitude of 7.7. The avalanche originated from a partially overhanging second half of the 17th century in Bolivia
145
and
cliff at 5400 to 6500 m above sea level, where the fractured granite the late 19th century in East Africa
146
. From then,
rock of the peak was covered by a 30 metre thick glacier. The ava- glacier shrinkage was more or less synchronous
lanche, which had an estimated volume of 50 to 100 million m
3
, trav- with the global one. Shrinkage rates were strong-
elled 16 km to Rio Santa down a vertical drop of 4 km. Along its path, est in the 1940s, followed by a pause around the
the avalanche overrode a hill in the downstream area and completely 1970s with several front advances. Since then,
destroyed the city of Yungay, claiming about 18 000 lives. glaciers have again begun to retreat
134
.
Since the publication of IPCC 2001, evidence
Caraz
has increased that changes in the mass balance
of tropical glaciers are mainly driven by coupled
changes in energy and mass fluxes related to
interannual variations of regional-scale wet and
dry seasons. Variations in atmospheric moisture
content affect incoming solar radiation, precipi-
tation and albedo, atmospheric longwave emis-
sion, and sublimation. At a large scale, the mass
balance of tropical glaciers strongly correlates
Yungay
with tropical sea surface temperature anomalies
N and related atmospheric circulation modes
1
.
Ranrahirca
0 5 km
Mancos
1962 avalanche
1970 avalanche
Figure 6B.18: Ice avalanches of the Nevados Huascarán in Peru.
The severe events in 1962 and 1970 originated from Glaciar 511
Lewis Glacier,
and claimed many thousands of lives.
mid 1990s.
Source: Data from the World Glacier Monitoring Service, Zurich, Switzerland Photo: S. Ardito
and figure by UNEP’s DEWA/GRID-Europe, Geneva, Switzerland
142 GLOBAL OUTLOOK FOR ICE AND SNOW