AS: A Case study on mass movement MEDC vs. LEDC contrast

Example of a (accelerated by man) Landslide in a MEDC:  Abbotsford Landslide, Dunedin, NZ 1979

Cause:

•              1978 families noticed cracks appearing in their homes.

•              1979 workmen discovered that a leaking water main had been pulled apart. Geologists discovered that water had made layers of clay on the hill soft, and the sandstone above it was sliding on this slippery surface.

•              Construction of the nearby Dunedin southern motorway, an earthquake that occurred in the area in 1974, deforestation (reduced evapotranspiration), increased urbanization (involved cutting into slope and infilling) and quarrying activity on the toe of the slope in the decades before may have further affected the land’s stability.

The landslide:

•              On July 27^th the slide began to accelerate.

•              Early warning system was put in place by Civil defense and a civil emergency was declared on the 6^th of August 1979. This was not thought to have been necessary, as geologists believed the slope would only move slowly.

•              However on the 9^th of August a 7 ha section of East Abbotsford started moving down the slope at a rate of 3m per minute, taking houses with 17 people inside.

•              It was essentially a block of sandstone resting on a bed of weaker clay. Displacement of 50m took place in about 30 minutes, leaving a small rift 30m deep in the head of the slope. In addition the slope was on an angle of 7⁰. Water collected in the impermeable clay, reduced its strength and cohesion, and caused the sandstone to slip along the boundary of the two rocks.

•              The sandstone involved 5.4 million m³ of material. At first the land moved as slow as soil creep, followed by a rapid movement with speeds of 1.7 m per minute.

Impacts:

•              Nobody was killed but 69 homes were destroyed or damaged and 200 people were displaced. The total cost from the destruction of the homes, infrastructure and relief organization amounted to £7 million ($10-13 million NZ today). In total 18 ha was affected.

•              Insurance schemes and government relief to cope with such disasters meant that residents were compensated for any damage.

•              However other impacts such as depressed housing prices, trauma and the cost of a prolonged inquiry were not immediately appreciated.

•              Lessons on landslide preparedness, and the affect human activity has on slopes can be learnt from this.

Case Study on a Physical Landslide in a LEDC: Vargas State, Venezuela  - 1999

Causes:

•              First two weeks of December 1999 saw an unusually high amount of precipitation (40-50% above normal rainfalls).

•              Political corruption – allowing shanty-towns to be built on steep slopes surrounding Caracas. The slopes around the region were changed to accommodate vast squatter settlements.

Landslide:

•              15-16^th December the slopes of the 2000m Mt Avila began to pour forth rock and mud burying 300 km stretch of the central coast.

•              Rains triggered mudslides, landslides and flash floods in between the mountains and the Caribbean Sea.

•              Search and rescue were deployed to search for survivors but very few were found in the first few days.

Impacts:

•              Rains triggered mudslides, landslides and flash floods which claimed the lives of 10,000 -50,000 (unknown accurately as most people were buried under mud or swept to sea) in between the mountains and the Caribbean Sea.

•              150,000 were left homeless by landslides and floods in the states of Vargas and Miranda.

•              Slum dwellings were often buried by mudslides (8-10m deep) or swept out to sea. This is why fatalities are unknown as many went missing and entire families went unreported as missing.

•              Bridges, roads, factories, crops, telecommunications and the tourism industry (in the immediate future) were destroyed. The international airport in Caracas was closed.

•              Containers at the seaport of Maiqueita were damaged. Harzardous material leaked out of these containers. Operations at the port were halted and hampered efforts to bring in emergency supplies. The economic damage was estimated at $3billion.

•              70% of Venezuelan population was living in this small coastal area. The government then made a plan to move some of the population to inland areas.

•              As a result of these landslides a plan to rebuild 40,000 homes was created for Vargas. A $100 million extension was planned for the international airport. The country’s main seaport in Vargas, was also planned to be modernized. Tourist destinations in Macuto and Camuri Chico were also rebuilt. Towns such as Carmen de Uria were not rebuilt, and instead created into parks & bathing resorts.

•              These improvements reduced the number of fatalities to 14 in the next 2005 mudslides in the region.