1. Case Study: Nevado Del Ruiz - 1985
Where did it happen?Nevado Del Ruiz is a stratovolcano found in west
Colombia where the Nazca plate is being subducted beneath the South
American plate. The latest eruption was ash plumes in January 2013.
What happened?
First seismic activity noticed in 1984. These included fumarole
activity, deposits of sulphur on the summit of the volcano and phreatic eruptions.
11th
September 1985 major phreatic eruption shoots steam high into the air.
Volcanic activity decreases during October1985 but increases during November 1985.
At 9:09pm on November 13th
1985 Nevado Del Ruiz erupts sending ash 30km into the air.
The total mass of the erupted material was 35 million metric tons.
The eruption produced pyroclastic flows which melted glaciers and snow on the summit. This
caused lahars which ran down the volcano’s sides at 40 miles per hour and reached a
maximum width of 50m.
Why did it happen? As the Nazca plate is subducted beneath the South American plate it melts. This
magma is lighter because it is mixes with gases, water and soil from the surface. The magma rises
forming a volcano. The pressure builds up until eventually the volcano erupts. The lahars were formed
when the heat from the eruption melted glaciers on top of the volcano. The water from the glaciers
mixes with volcanic debris and surges down the volcano.
Primary effects Secondary effects
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The pyroclastic flows melted
glaciers forming lahars which
were 30m deep, 50m wide and
travelled at 12m per second.
150000 animals killed by lahars.
Land made more fertile by the
mud from the lahars.
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3400 hectares of agricultural land
was lost in the eruption.
Cost the Colombian economy
$7.7billion dollars, 20% of GDP
for 1985.
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All roads and communications
were destroyed in the areas
affected by the eruption.
50 schools, 2 hospitals, 58
industrial plants and 343
23000 people were killed by the
lahars and 5000 were injured.
8000 people were made homeless
The Armero tragedy – a lahar

2. l commercial establishments were
damaged or destroyed.
Damaged water supplies
swept through a town killing ¾ of
the inhabitants.
Immediate responses Long term responses
Colombian Red Cross and Civil Defence
personnel were the first to organize
rescue and medical care.
Colombian military provided helicopters
to airlift victims for medical care,
distributed supplies and established field
medical care and shelter facilities
Health workers administered 80000
doses of tetanus and typhoid vaccines.
Colombia established a plan for warning
and evacuation of areas at risk from
another eruption.
Public education campaign started in
early 1986 to educate people about the
dangers of the volcano.
Red Cross circulated flyers about the
volcanic hazard with information about
evacuation procedures and warning
systems.
Hazard maps distributed in towns.
Evacuation route markers were painted
on buildings.
How was the hazard managed? The hazard was not managed because despite many warning signs a
year before the eruption there was no evacuation of areas at risk in spite ofscientists saying there was
a risk of lahars. A hazard map was published but it was poorly distributed and had many errors such
as, there was no key to indicate what colours meant on the map. Many people who survived the lahars
said they had not seen the map.
Why was the death toll so high?The death toll was so high because there was no evacuationand
people living in places such as Armero were unaware of continuing activity. Plus 3 days after the
disaster the government still had no plan of action plan which prevented government aid from
reaching people in need.