Transcript Natural Hazards Case Studies - Chew Valley School | Intranet

Natural Hazards Case Studies
One Tectonic hazard event in an LEDC
 Nevado Del Ruiz, Colombia
Nevado Del Ruiz
 Nevado del Ruiz is the
northernmost of several
Colombian stratovolcanoes in the
Andes Volcanic Chain of western
South America. The Andean
volcanic belt is generated by the
eastward subduction of the
Nazca oceanic plate beneath the
South American continental plate.
Typically, such stratovolcanoes
generate explosive Plinian
eruptions with associated
pyroclastic flows that can melt
snow and glaciers near the
summit, thus producing
devastating lahars.
Key terms
 Plinian – volcanic eruption with columns of gas and volcanic ash
 Stratovolcano – also known as a
Conical volcano
 Pyroclastic flow
- Fast flowing hot
Gas and rock
 Lahar – mudflow made of pyroclastic flow and water
Nevado Del Ruiz
After nearly a year of minor earthquakes and steam explosions from Nevado del
Ruiz, the volcano exploded violently on November 13, 1985. The initial blast began at
3:06 p.m., and two hours later pumice fragments and ash were showering down on
Armero. However, the citizens of Amero remained calm. They were placated by
reassuring messages from the mayor over radio, and from a local priest over the
church public address system. Nevertheless, the Red Cross ordered an evacuation of
the town at 7:00 p.m. However, shortly after the evacuation order the ash stopped
falling and the evacuation was called off.
 At 9:08 p.m., just as calm was being restored, molten rock began to erupt from the
summit crater for the first time (all previous eruptions were steam explosions). The
violent ejection of this molten rock generated hot pyroclastic flows and airfall
tephra that began to melt the summit ice cap. Unfortunately, a storm obscured the
summit area so that most citizens were unaware of the pyroclastic eruption.
Meltwater quickly mixed with the erupting pyroclastic fragments to generate a
series of hot lahars. One lahar flowed down the River Cauca, submerging the village
Chinchina and killing 1,927 people. Other lahars followed the paths of the 1595 and
1845 mudflows. Traveling at 50 kilometers per hour, the largest of these burst
through an upstream damn on the River Lagunillas and reached Armero two hours
after the eruption began. Most of the town was swept away or buried in only a few
short minutes, killing three quarters of the townspeople.

Eye witness account

"We didn't hear any kind of alarm, even when the ash was falling and we were in the hotel . . . we turned on the radio . . . The mayor was
talking and he said not to worry, that it was a rain of ash, that they had not reported anything from the Nevado, and to stay calm in our
houses.There was a local radio station and we were listening to it, when suddenly it went off the air . . . about fifteen seconds later, the electric
power went out and that's when we started hearing the noise in the air, like something toppling, falling, and we didn't hear anything else, no
alarm . . .The priest from Armero had supposedly spoken on a loudspeaker [around 6:00 p.m.] and had said the same thing: that there was no
need to leave Armero . . .When we went out, the cars were swaying and running people down . . . there was total darkness, the only light was
provided by cars . . . we were running and were about to reach the corner when a river of water came down the streets . . . we turned around
screaming, towards the hotel, because the waters were already dragging beds along, overturning cars, sweeping people away . . . we went back to
the hotel, a three-story building with a terrace, built of cement and very sturdy . . . Suddenly, I heard bangs, and looking towards the rear of
the hotel I saw something like foam, coming down out of the darkness . . . It was a wall of mud approaching the hotel, and sure enough, it
crashed against the rear of the hotel and started crushing walls . . . . And then the ceiling slab fractured and . . . the entire building was
destroyed and broken into pieces. Since the building was made of cement, I thought that it would resist, but the boulder-filled mud was coming
in such an overwhelming way, like a wall of tractors, razing the city, razing everything . . . .Then the university bus, that was in a parking lot
next to the hotel, was higher than us on a wave of mud and on fire, and it exploded, so I covered my face, thinking this is where I die a horrible
death . . .There was a little girl who I thought was decapitated, but . . . her head was buried in the mud . . . A lady told me, 'look, that girl
moved a leg'.Then I moved toward her and my legs sank into the mud, which was hot but not burning, and I started to get the little girl out,
but when I saw her hair was caught, that seemed to me the most unfair thing in the whole world." -- from A. Scarth (1999)
One Tectonic hazard event in an MED
 Mount Etna 2002
Mt Etna
 Mt Etna Volcano is one of the world's most active volcanoes. It has
been erupting since several million years. Mt Etna is one of the
greatest and beautiful volcano adventure tour destinations in
Sicily, beside many other which can be easily enjoyed from our
charming village of Taormina. This volcano has more than 400
craters, split all over the Catania county. To the ancient Greeks,
Mount Etna was the realm of Vulcan, god of fire, and the home of
the one-eyed monster known as the Cyclops. Etna offers skiing in
the Winter months and breathtaking hikes in the woods during the
Summer. There are also a number of smaller peaks on the slopes of
Etna, and some interesting caverns. Since Etna is a strato volcano,
with relatively cool lava temperatures and numerous openings
(vents), nobody ever knows precisely where on its vast surface the
next eruption will be.
Group 5
Mt Etna 2002-2003
 A rift had began to open and the volcano looked dangerous again
after a few hours various craters opened between 2700 and
2200m.s.l.m.long the rift on the western side of the volcano
The Facts
 On 29th of October on the fracture towards valley along the North-
east rift, twelve craters approximately between 2000-1800mt.
from which emitted a Strombolian type intensive explosive activity.
The following day earthquake of 3-4 on the Richter scale, seriously
damaged many villages in the eastern area of Etna
Pictures
Mt Etna
 An October 2002 eruption of Mount Etna, a volcano on the Italian
island of Sicily, as seen from the International Space Station. Etna is
the largest of Italy’s three active volcanoes and one of the most
active in the world. This eruption, one of Etna’s most vigorous in
years, was triggered by a series of earthquakes. Ash fall was
reported as far away as Libya, 600 km (373 mi) to the south.
Where is Mt Etna? (map)
What causes Mt Etna to
erupt?
Why do people live near Etna?
Eruption of Mt
Etna in 2002
How to people respond to the eruptions of
Mt Etna?
What were the primary and secondary
effects of the eruption
One Climatic hazard event in an LEDC
 Cyclone Nargis, Myanmar 2008
Distribution of tropical storms
Cyclone
Nargis
Inside Burma after the cyclone
 Watch the video link and write 5 statements of
what you feel about the cyclone in Myanmar
Where is Myanmar? (map)
What was the environmental
damage of Cyclone Nargis?
Characteristics of Myanmar
Cyclone Nargis,
Myanmar 2008
What were the social and economic effects
of Nargis?
How did people respond to Cyclone Nargis?
One Climatic hazard event in an MED
 Hurricane Katrina 2005
Distribution of tropical storms
Hurricane
Katrina
Hurricane Katrina
General information
2. Effects of the hurricane on people and economy
3. Reasons why response was so poor
1.