Case Study: Mass Movement (DP IB Geography)

Revision Note

Case Study: Vargas, Venezuela

Vargas mass-movement facts

  • Location – Vargas state, Venezuela

  • Date – 15–16th December 1999

  • Cause – Rainfall 40–50% above the usual average

  • Events – Rainfall triggered flows of soil and debris

  • Type of mass movement – Fast-moving debris flow

Hazard event

  • Thousands of debris flows moved rapidly down the steep-sided mountains and narrow canyons

  • The debris flow included boulders up to 10 metres in diameter

  • In some places, the deposits created by the debris flow were several meters thick

  • The debris flow speed was estimated at between 3 and 14.5 metres per second

Impacts

  • Rain caused many mudslides, landslides and debris flows across the region

  • There were between 10,000–50,000 deaths (many people were never found, and whole families were buried by the mudslides or swept out to sea)

  • Over 150,000 people were made homeless

  • Towns including Cerro Grande and Carmen de Uria were completely buried or swept away

  • Over 70% of the population in Vargas state were affected

  • The debris flow and mudslides destroyed many squatter settlements 

  • Bridges and roads were destroyed

  • The seaport at Maiquet was affected, leading to hazardous material leaking from containers

  • Crops were destroyed

  • Economic damage was estimated at US$3.5 billion

  • Communication systems were destroyed 

  • Supplies of food and water were affected for months

  • Looting occurred across the region, meaning martial law had to be implemented for over a year

Factors affecting vulnerability

  • The debris flows killed thousands of people as a result of a range of factors:

    • High population density in the coastal areas

    • Disorganised urban growth 

    • Poor quality buildings – many of the areas affected were squatter settlements

    • Corruption amongst government and public officials, which allowed homes to be built in vulnerable areas

    • In 1999, the government stopped collecting rainfall information:

      • This data was used to maintain bridges, reservoirs and other infrastructure

    • Lack of warning – no evacuation orders were issued

    • The government ignored a report from the Civil Defense Agency that urged them to declare a state of emergency 12 hours before the main debris flows

Case Study: Ponzano, Italy

Ponzano facts

  • Location – Ponzano, Italy

  • Date – February 2017

  • Cause – Combined effect of earthquakes and snowmelt leading to saturated soil and intense rainfall (81mm in four days)

  • Type of mass movement – Slow-moving landslide

Hazard event

  • The rate of landslide movement averaged one metre per day for two weeks

  • Ponzano village in the north-east of Italy, about 30km north of Venice

Impacts

  • An estimated 7 million m3 of material moved

  • Over 100 people evacuated from 35 houses

  • Collapse of several buildings

  • Agricultural land around the village becoming unsafe to cultivate

Factors affecting vulnerability

  • Low population density

  • The slow movement of the landslide made evacuation easy

  • The landslide was monitored and tracked by the Civil Protection Department

  • Emergency services supported people to recover property from evacuated buildings

  • Psychologists were provided to support people's mental health

Examiner Tip

When considering hazard events it is important that you can explain why vulnerability varies between and within communities.

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