Download MT ST Helens and NEVADO DEL RUIZ

VOLCANOES
MT ST HELENS/RURAL/MEDC
Date
18th May 1980
Place
Mt. St. Helens, Cascade Range, Washington State, USA
Plates
North American plate/Juan de Fuca plate- Destructive boundary
Type of
 Minor earthquakes and small dust and ash cloud followed by:
eruption
 North side bulged, landslide of rock into Spirit Lake
 Massive explosion causing a blast zone and pyroclastic flow
 Series of eruptions of gas, ash and volcanic bombs
 Dust and ash combined with meltwater from glaciers to cause mudflows(lahars)
 Huge dust and ash cloud which eventually encircled the earth
Effects



60 died
Logging camps destroyed
Rivers heated and chocked with sediment so all fish died. Salmon and trout
fishing area with hatcheries
 Road and railway bridges washed away
 Cars stalled in dust
 Every tree within 25 sq km destroyed
 Electricity and phone lines cut
 Wildlife in whole area lost
 Crops and cattle lost from flooding and dust clouds
Mt. St. Helens has become a National Park with thousands of visitors a year. Gradually plant and animal
life is coming back to the area
NEVADO DEL RUIZ/RURAL/LEDC
Date
Nov 13th 1985 9.00pm
Place
Nevado del Ruiz, Andes Mts, Columbia
Plates
South American plate/Pacific plate- Destructive boundary
Type of
 Minor earthquakes and small dust and ash clouds for several months followed
eruption
by:
 Explosion causing pyroclastic flow and dust and ash cloud
 Dust and ash combined with meltwater from glaciers to cause mudflows(lahars)
 Series of lahars which carry with them rocks, soil and trees and they sweep
down valley, in places up to 5 metres deep
Effects
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


25,000 died
Town of Armero destroyed
Rivers heated and chocked with sediment
Road and railway bridges washed away making access for rescue services
difficult. Only access was by helicopter
 Electricity and phone lines cut
 Wildlife in area lost
 Crops and cattle lost from flooding and dust clouds
The site of Armero has been preserved as a national monument to all who died in the disaster. The rescue
effort was chaotic because the country was ill prepared, access was difficult and politicians and world news
teams commandeered helicopters. Equipment and medicines needed for injured was very slow to arrive,
often unsuitable or broken so that many survivors died afterwards.