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LITHOSPHERIC PROCESSES, HAZARDS AND MANAGEMENT:
MASS MOVEMENT CASE STUDIES
Natural causes
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Earthquakes  avalanche, rock fall
o Eg. 7.7-magnitude earthquake in Peru, 1970
o There was loosened a mass of unstable ice and snow near the summit of Huascaran,
causing an avalanche that was travelling at a speed of 480km/h, triggering rock falls
along the way. The avalanche hit the town of Yungay with a population of 20,000 people.
Rescue workers took three days to reach the town. Very few survivors were left.
Volcanic eruption  mudflow
o Eg. eruption of Nevado del Ruiz in Colombia, 1985
o Prior to the eruption, the warming peak melted snow and ice caused a 20m mudflow
which travelled 27km down the Lagunillas Valley.
o On the day of eruption, more meltwater was released to produce a 30m mudflow which
travelled down the valley at over 80km/h. The mudflow buried the town of Armero to
8m deep and killed 21,000.
Hurricane  landslide, mudflow
o Eg. Hurricane Mitch off the Caribbean coast of Honduras, 1998
o Torrential rains over a few days caused landslides that affected 3 million people
o In Nicaragua, heavy rain falling onto Volcano Casita caused mudflows that killed 1,900
people and virtually destroyed the town of Posoltega.
Human causes
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Dam  landslide
o Eg. Vaiont Dam in Italy, 1963
o The dam was built in a narrow valley with steep sides consisting of alternate layers of
clays and limestone. Heavy rain saturated the clay, causing a landslide of rocks, clay and
mud into the reservoir. The displaced water spilled over the dam and swept down the
valley, destroying the town of Longarone. 1,900 people died. A court enquiry concluded
that the site was geologically unstable and that even during construction many smaller
landslides had occurred. The dam was eventually closed.
Dumping waste material  mudflow
o Eg. Coal waste storage in Aberfan, 1966
o The waste were dumped on slopes of 25°, over 200m above the town and unknowingly,
on a line of springs. Water from the springs added weight to the waste heaps, increasing
shear stress. Heavy rain resulted in mudflow that contained over 100,000m3 of material,
engulfing part of the Aberfan town. There were 147 deaths. The potentially dangerous
waste have been lowered, regarded and landscaped since.
©caughtingeog 2013.
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Urbanisation
o Eg. building on slopes in Hong Kong, 1948-1998
 Landslips have been responsible for 480 deaths. These landslips are due to the
inadequacies of hillside construction works and deficiencies in maintaining
slopes ocne they are utilised.
 In 1966, torrential rainstorms triggered massive landslides which killed 64
people, displaced 2,500 and caused 8,000 to be evacuated. In 1977, the
Geotechnical Engineering Office (GEO) was set up to better manage the slopes
eg. advise on land-use plans, undertake landslide warning and emergency
services.
 BUT in 1997, most of Hong Kong experienced over 300mm of rain in 24 hours. At
the centre of the storm, 110 mm fell in one hour and 800mm in the day,
resulting in landslides. One person died, and 8 were injured, which shows
success of management by the GEO.
o Eg. slums in Rio, 1966 and 1967
 The poor in Rio build their shanties at the sides of the hills above the city.
Torrential rains in 1966 caused mudslides, killing 239 and injuring hundreds of
residents as their houses were swept away or crushed by the mud. But the
people believed that the incident was only a rare one and so did not address it.
 In 1967, an 11-inch rainfall caused mudslides again and crept into Rio’s three
power plants, cutting the city’s electrical supply to 40%. The death toll was 259.
After the incident, the governor prohibited more construction in and about the
hills and instituted new laws to prevent the destruction of vegetation. Concrete
shorings were also set into the slopes.
o Eg. undercutting in India
 A landslide occurred in Himachal Pradesh in 1995 that killed 65 people because
of the undercutting of the slope of an alluvial fan that over-steepened the slope.
o Eg. cliff-top building in Scarborough, 1993
 The back garden of Holbeck Hall Hotel collapsed due to a rotational slump. Clifftop development took place despite the cliff being constantly eroded, and the
top layers of the cliff being made of boulder clay, unconsolidated material
deposited by retreating glaciers.
 BUT this was following a number of drier than average summers, and a
particularly wet spring in the year.
©caughtingeog 2013.