Geomorphology applied to glacial regions
135
drain the lake in order to avoid the spilling and subsequent destruction of the moraine dam.
A catastrophic destruction of an end-moraine lake occurred in the Santa Ana river valley
of the Peruvian Andes on 15 March 1941. It resulted in a large flood that destroyed the
village of Huaraz, causing the death of 6000 people (Hambrey and Alean, 1992).
Numerous such examples are also known in the Himalayas as well.
2.4. Volcanism and glaciers
When the heat liberated by volcanic activity affects glaciers, a sudden ice melt can occur.
The resulting water, mixed with volcanic ash, results in lahars or volcanic mudflows that
move by gravity, affecting human settlements and activities located at the foot of the
volcano. If the melt waters achieve large volumes, then quite dramatic floods can be
triggered. Three examples from different parts of the world serve to illustrate the dramatic
development of lahars and their significant consequences in both human lives and
economic losses. The crater lake of Ruapehu volcano (2797 m), located on the North
Island of New Zealand, broke out along with significant ice and snow melt on Christmas
eve, 1953, causing a lahar that destroyed a railway bridge immediately before the passage
of a train. The locomotive and five cars fell into the river and 151 people died (Francis,
1993).
The Mount St. Helens volcano (2950 m), located in the state of Washington, in the
Cascades Range, USA, begun its eruption on 18 May 1980, though its activity had started
2 months before with earthquakes and small phreatic eruptions. The volcano was subject
to close vigilance in hopes of avoiding greater problems (Crandell et al., 1975; Wesson,
1983). The big eruption caused by the landslide failure of the north face of the mountain,
lowered the height of the volcano ---400 m and triggered large ice avalanches. The ash
resulting from the explosion covered the neighbouring glaciers, which advanced in the
following few years as a consequence of the protection against solar radiation. On the
other hand, large lahars of up to 30 km in length developed, destroying houses and forests.
Some dams restrained them, and in other cases the trees contributed to damming the waters
in the bridges, resulting in floods when the bridges broke. Fifty-seven people died as a
consequence of this eruption, and the economic losses were estimated to be about $1000
million dollars (Lipman and Mullineaux, 1981; Hickson and Peterson, 1990).
The Nevado del Ruiz volcano (5400 m), located in the Colombian Andes at 5 ~ north
latitude, has an ice field in its summit. On November 13th, 1985, it had a low magnitude
eruption, with the emission of a few pyroclastic products. The eruption, as in previous
cases, was forecast 1 year before due to seismic activity and one phreatic explosion. In
spite of the low energy of the eruption, ice and snow avalanches were triggered, and
the hot ash melted ice masses; the resulting waters carried a large quantity of recent and
old ash, causing lahars or volcanic mudflows running toward the densely inhabited valleys
(Figure 6.11). The lahars developed in two main stages. On the east slope they were
channelized by the Lagunillas fiver, with velocities of 30 to 40 km h-1, until at midnight
they reached the city of Armero, located 60 km away from the volcano. The village
was buried in a few minutes by the lahars and 22,000 people died. On the west-facing
slope in the locality of Chinchinfi, mudflows killed 2000 people (Parra and Cepeda,
1990; Voight, 1990).
135
drain the lake in order to avoid the spilling and subsequent destruction of the moraine dam.
A catastrophic destruction of an end-moraine lake occurred in the Santa Ana river valley
of the Peruvian Andes on 15 March 1941. It resulted in a large flood that destroyed the
village of Huaraz, causing the death of 6000 people (Hambrey and Alean, 1992).
Numerous such examples are also known in the Himalayas as well.
2.4. Volcanism and glaciers
When the heat liberated by volcanic activity affects glaciers, a sudden ice melt can occur.
The resulting water, mixed with volcanic ash, results in lahars or volcanic mudflows that
move by gravity, affecting human settlements and activities located at the foot of the
volcano. If the melt waters achieve large volumes, then quite dramatic floods can be
triggered. Three examples from different parts of the world serve to illustrate the dramatic
development of lahars and their significant consequences in both human lives and
economic losses. The crater lake of Ruapehu volcano (2797 m), located on the North
Island of New Zealand, broke out along with significant ice and snow melt on Christmas
eve, 1953, causing a lahar that destroyed a railway bridge immediately before the passage
of a train. The locomotive and five cars fell into the river and 151 people died (Francis,
1993).
The Mount St. Helens volcano (2950 m), located in the state of Washington, in the
Cascades Range, USA, begun its eruption on 18 May 1980, though its activity had started
2 months before with earthquakes and small phreatic eruptions. The volcano was subject
to close vigilance in hopes of avoiding greater problems (Crandell et al., 1975; Wesson,
1983). The big eruption caused by the landslide failure of the north face of the mountain,
lowered the height of the volcano ---400 m and triggered large ice avalanches. The ash
resulting from the explosion covered the neighbouring glaciers, which advanced in the
following few years as a consequence of the protection against solar radiation. On the
other hand, large lahars of up to 30 km in length developed, destroying houses and forests.
Some dams restrained them, and in other cases the trees contributed to damming the waters
in the bridges, resulting in floods when the bridges broke. Fifty-seven people died as a
consequence of this eruption, and the economic losses were estimated to be about $1000
million dollars (Lipman and Mullineaux, 1981; Hickson and Peterson, 1990).
The Nevado del Ruiz volcano (5400 m), located in the Colombian Andes at 5 ~ north
latitude, has an ice field in its summit. On November 13th, 1985, it had a low magnitude
eruption, with the emission of a few pyroclastic products. The eruption, as in previous
cases, was forecast 1 year before due to seismic activity and one phreatic explosion. In
spite of the low energy of the eruption, ice and snow avalanches were triggered, and
the hot ash melted ice masses; the resulting waters carried a large quantity of recent and
old ash, causing lahars or volcanic mudflows running toward the densely inhabited valleys
(Figure 6.11). The lahars developed in two main stages. On the east slope they were
channelized by the Lagunillas fiver, with velocities of 30 to 40 km h-1, until at midnight
they reached the city of Armero, located 60 km away from the volcano. The village
was buried in a few minutes by the lahars and 22,000 people died. On the west-facing
slope in the locality of Chinchinfi, mudflows killed 2000 people (Parra and Cepeda,
1990; Voight, 1990).