15
1. Internal geological processes
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5.1.1.
Seismic risk in Spain
The Iberian Peninsula is situated near the contact region
of the African and the Eurasian plates, although it is not a
very active area.
As a result, there is a moderate seismic risk, less than in
most other Mediterranean countries. This means that
there are earthquakes which are felt by the population and
more rarely, others that cause considerable damage.
Catastrophic earthquakes in this area cannot be ruled
out, such as the one in Arenas del Rey (Granada) in
1884, which caused more than 1 000 deaths, or the
most recent one in Lorca (Murcia) in 2011, which caused
nine deaths.
5.2.
Volcanic risk
The risks associated with volcanic activity are quite varied,
as you can see in the following figures and examples:
Seismic risks
in Spain: maximum intensity expected in a 500 year period
(source: IGN)
Analyse
37.
Look at the map. Listen and answer the questions.
INTENSITY
< 6
= 6
= 7
= 8
0
1
2
3
4
5
6
7
8
Height
of cloud
Plinian
Vulcanian
Hawaiian
VEI Volume
of ash
Type of
eruption
0.0001 km
3
0.001 km
3
0.01 km
3
0.1 km
3
1 km
3
10 km
3
100 km
3
1000 km
3
< 0,1 km
0,1 - 1 km
1 - 5 km
3 - 15 km
10 - 25 km
>25 km
acid
rain
ash cloud
falling ash
prevailing wind
lava
stream
lahar (mudflow)
earthquakes
landslide
pyrocrastic
flow
pyrocrastic
flow
VEI (volcanic explosivity index)
Analyse
39.
TheVEI is used tomeasure
thedangerofaneruption.
Look at the graph. What
two factors determine
the VEI? What is the
maximumheight that ash
clouds can reach?
Risks associated with volcanic activity
❚❚
The eruption of Laki (Iceland) in 1783-84
released so much ash and gases into
the atmosphere that temperatures in
the northern hemisphere went down
substantially, causing losses of crops
and starvation.
❚❚
On 27 August 1883 the explosion
of Krakatoa in Indonesia produced a
tsunami that caused 36000 deaths.
❚❚
On 8May 1902 a pyroclastic flow from
the volcano Mount Pelèe destroyed
the city of St. Pierre (Martinique Island)
killing 28000 people.
❚❚
On13November1985asmalleruption in
the Nevado del Ruiz volcano (Colombia)
melted part of snowy summit causing
a lahar that buried 23000 people.
❚❚
On 21 August 1986 a cloud of carbon
dioxide froma volcano caused thedeath
of 1746 people due to suffocation in
Cameroon.
❚❚
On 17 January 2002 the streams of lava
from the Nyiragongo volcano caused
close to one hundred deaths in the
city of Goma (Zaire).
Understand
38.
Explain why lava flows are an important volcanic risk.
