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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