Natural Hazards Case Studies

Mass Movement

Hollbeck hall 1993

• A landslip along the upper sections of boulder clay, at the 60m cliffs in Scarborough.

• Destroyed the 1883 Hollbeck hall.

• Its part of the most rapidly retreating area in Britain; would have cost too much to protect it.

• Agriculture blamed droughts for making the land unstable.

• It rained, the clay became saturated, causing an earth flow.

• Nothing to do with erosion.

• Nothing could be done until the slope slid to 25 degrees.

Swiss Alps 2007

• Avalanche

• Caused by: Heavy snowfall 75cm, mild winter so warmer layers, trees removed to help skiers, strong winds built up-drift, skiers went off piste, slopes reshaped for hotels.

• Impacts: 8 killed, some damage to buildings, high cost of rescue services, roads blocked.

• Responses: short term – rescue services, helicopters. Long term – fence off avalanche prone areas, structures to slow or divert avalanches, warnings and education, setting off potential avalanches, reforestation.

Aberfan 1966

• Flow/landslide

• Causes – Waste coal tip at a steep angle, prolonged heavy rain, tip built on a spring so water seeped through sandstone, little vegetation to bind the waste, no management of tip, assumed any slide would be slow.

• Impacts – 147 killed, 116 were children, 20 houses and a farm buried, huge physiological impact, loss of a generation, cost of clean up, it was slow enough to give a warning.

• Responses – short term: emergency rescue services. Long term: £20 million in clean up, no prosecutions, over £20 million in donations, 1969 Mines and Quarry Act passed which controls the siting of tips, other tips checked and their slope angles reduced.

Venezuelan Mudslide 1999

• High rainfall (410mm in one day)

• Precipitation 40% higher than average.

• Started with an avalanche of rocks/mud pour down slopes of 2000m Mt Avila, burying 300m of land.

• The rain triggered mudslides, landslides and flash floods that killed 30-50,000 people in a ***** between the mountains and the Caribbean sea.

• 150,000 became homeless.

• Slums were buried and swept out to sea.

• The mud was 30ft deep.

• Infrastructure was destroyed.

• Airport closed

• Ports flooded so supplies couldn’t be brought in.

• Container ships were damaged and hazardous materials leaked.

• Total cost $3 billion.

• Blamed corrupt politicians for allowing shanty towns to develop around the mountain.

• Search and rescue, few survivors found.

• Emergency relief, accommodation, food, water and medicine.

• Encouraged people to move away from overcrowded coast.

• Government announced it was to expend the city and build homes in the north coastal region.

• Reconstruction of canels and ports.

• Vargras built quickly.

• The town ruined was replaced with parks.

Flooding

North Sea Storm Surge 1953

• Physical causes – Storm surge: strong winds from north/east pushing water south, intense depression so sea level rose, high spring tide, north sea narrows towards south so greater wave size, heavy rain so rivers swollen.

• Human causes – Dredging of sand offshore, neglected sea walls, global warming so sea level rise, salt marshes reclaimed, rivers embanked, rapid urbanisation of coast, encroachment onto natural flood holding areas.

• Enviro impacts: Land lost to…