Transcript Tectonic hazards human impacts - School

6GEO4 Unit 4 Tectonic Activity and Hazards
What is this option about?
• The Tectonic Activity and
Hazards option focuses on the
range of natural hazards
generated by plate tectonics
• In addition to understanding
why these hazards happen, you
will need to understand:
• The impact of tectonic
processes on the landscape
• The impact of tectonic hazards
on people
• The ways in which people
respond to, and try to manage,
natural hazards.
Primary hazards
Secondary
hazards
Earthquakes
Tsunami
Landslides
Liquefaction
Volcanoes
Lahars
Landslides
Tsunami
CONTENTS
1.
2.
3.
4.
Tectonic activity and causes
Tectonic hazards physical impacts
Tectonic hazards human impacts
Response to tectonic hazards
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1. Tectonic activity and causes
• Tectonic activity can produce a
very large range of hazard events
• Not all of these events are
‘disasters’
• A natural hazard event becomes
a disaster when the event causes
a significant impact on a
vulnerable population.
• These impacts could be human
(death, injury) and / or economic
(property losses, loss of income).
• Definitions vary, but ‘significant’
losses usually means 10+ deaths /
100+ affected / $1 million losses.
The Dregg disaster model
Event profiles
• Not all tectonic hazards are the same
• Event profiles are a common way of comparing
different hazards
• In this example the 2004 Asian Tsunami and ongoing
eruption of Kilauea on Hawaii are compared
• Hazard profiles can be drawn for any event.
Earth’s heat engine
• Tectonic processes are
driven by radioactive
decay in the core
• This decay generates
heat inside the earth,
which drives vast
convection currents
• This convection is
largely responsible for
plate movement
Tectonic settings and plates
• Most tectonic hazards are concentrated at plate margins
(boundaries), although ‘hotspots’ are a notable exception.
• Different types of boundary generate very different tectonic
hazards.
The range of volcanic hazards
• Dangerous volcanic
hazards are found
along subduction
zones at destructive
plate margins
• The most dangerous
volcanoes are
themselves multiple
hazard areas.
• Volcanoes at
constructive plate
margins (Iceland) and
oceanic
hotspots(Hawaii) are
much less hazardous
and destructive.
Magma generation
• Magma, molten rock in the earth’s crust, has an important relationship
with volcanic explosivity and hazard level
• Andesitic magmas, formed by wet partial melting at subduction zones
produce highly explosive and destructive composite volcanoes
Magma
type
Generation
Basaltic
Dry partial melting of
upper mantle
Low silica, low gas, low
viscosity.
Andesitic
Intermediate
Rhyolitic
High silica, high gas, high
viscosity.
Tectonic setting
Oceanic Hot spot (Hawaii)
Constructive (Iceland)
Hazards
Lava flow
Wet partial melting of Destructive plate margin
subducting plates
(Andes)
Island arc margin
(Montserrat)
Lava flow, ash and tephra,
pyroclastic flow, lahar, gas
emission
In situ melting of
lower continental
crust
(very rare eruptions)
Cataclysmic explosion,
pyroclastic flow
Continental Hot spot
(Yellowstone)
Continent collision zone
(Himalayas)
Measuring volcanic explosivity:
• The Volcanic
Explosivity Index (VEI)
is used to measure
volcanic power.
• VEI measures: Volume
of ejecta Height of the
eruption column
Duration of the
eruption.
• Modern humans have
never experienced a
VEI 7 or 8
Earthquakes
• Earthquakes are a very
common, sudden release of
energy that generate seismic
waves
• Most occur along faults (cracks
in the earth’s crust) which
become ‘locked’
• Opposing tectonic forces push
against the locked fault,
building up strain, which
eventually gives way releasing
stored energy
• This energy spreads out rapidly
from the earthquake origin (the
focus) reaching the surface at
the epicentre, and then
spreading horizontally.
Tsunami
• Tsunami are relatively rare events.
• They are generated by submarine earthquakes, volcanic collapse, and
coastal landslides, which suddenly displace huge volumes of water
• The 1993 Okushiri tsunami (Japan), 2004 Asian Tsunami and 2009 Samoa
events are all useful as case studies.
• Tsunami waves are radically different from normal wind generated ocean
waves.
• When a tsunami hits a coastline, the effect is more like a devastating
coastal flood than a single breaking waves
2. Tectonic hazards physical impacts
• Tectonic processes play a key
role in forming the landscape
around us
• Volcanic activity and the
movement of tectonic plates
create mountains, plateaux
and other landscape features
• These landscapes are then
modified by geomorphological
processes (weathering,
rivers, ice, wind and slope
processes)
Magma type and volcano morphology
• Volcanoes are extrusive igneous landforms. The form of volcanoes
is related to magma types, and therefore to different tectonic
settings:
• Basaltic – huge, low relief shield volcanoes plus small scoria cones
and fissure vents.
• Andesitic – steep sided strato-volcanoes; layers of lava, ash and
tephra.
• Rhyolitic – central craters with lava plugs / domes, due to high
viscosity of the lava. Calderas and collapse calderas.
Extrusive igneous activity
• Large scale outpourings of basaltic magma, called flood basalts,
have occurred at various times in the past.
• These produce distinctive lava plateaux and stepped or ‘trap’
topography
Intrusive igneous activity
• The injection (intrusion) of magma below the surface can
produce characteristic landforms
• Igneous rock normally resists weathering and erosion in
comparison to surrounding rocks, which produces positive relief
features.
• Large intrusions such as batholiths produce upland areas,
whereas minor intrusions produce smaller landscape features
Earthquakes and
faults
• Tectonic movements and movements along faults (which
generate earthquakes) also produce distinctive landforms and
relief:
Note: diagram not to scale
3. Tectonic hazards human impacts
• A surprising number of
people live in areas of
active tectonic processes
• Major tectonic hazards can
strike with devastating
force
• The 2005 Kashmir
Earthquakes killed around
85000, the 2008 Sichuan
‘quake over 65,000 and
200,000+ died in the 2004
Asian Tsunami
• It is important to consider
why people live, in such
large numbers, in areas of
great risk
Ignorance of the
risks and / or
underestimation
of risk
Choice e.g.
fertile
farmland or
tourism
Living in
areas of
tectonic
risk?
Nowhere else to
go / lack of
alternatives
Inertia;
always lived
there
Impacts
• Every hazard event is different, and therefore the specific
impacts of disaster vary
• When researching case studies, it is important to be able to
identify specific impacts and be able to explain these
• Some impacts are tangible and can be given a financial value.
Others are intangible, such as the destruction of a temple or
artwork.
• Many losses are direct and immediate such as property
damage, but others are indirect – these come later and are
harder to quantify, such as stress and psychological damage.
• Impacts are often considered as human (death, injury,
illness), economic (property loss, loss of income, cost of
relief effort) and physical (changes to landscape and
topography).
• Examine the two earthquakes below and consider how factors such as
economic development, building types, the geography of the area
affected and the relief effort may have affected the impacts
Details
(South Asian) Earthquake
October 2005, Kashmir
Magnitude 7.6. Huge number of
landslides accounting for 30%+
of deaths
(Wenchuan) Earthquake
May 2008, Sichuan, China
Magnitude 8.0. Thrust fault at continent
continent convergence
Fault
displacement
Focus depth
Largely horizontal
displacement of up to 10m
10 km
Up to 5m vertically and 4m horizontally at the
surface
19 km
Aftershocks
900+ over magnitude 4.0
250+ aftershocks over magnitude 4.0
Deaths
80,000
70,000
People affected
Injuries
8 million
3-4 million homeless
200,000+
15-30 million
5 million homeless
380,000
Damage estimate
US$5 billion
US$150 billion
Buildings
Around 1 million damaged/
destroyed / severely damaged
Over 2 million damaged
200,000+ buildings destroyed
Developed versus developing world
• It is often said that
disaster impacts in
the developed world
are largely economic,
whereas in the
developing world they
are human (death).
• You should carefully
consider if this
generalisation is true.
(see the table, right)
• The 1995 Kobe
earthquake in Japan
and 1991 eruption of
Mt Pinatubo in the
Philippines are useful
examples to consider
Death Toll
Event
Location
Date
5,115
Mount Kelut eruption
Indonesia
1991
23,000
Nevado del Ruiz eruption
Colombia
1985
Spitak Earthquake
Armenia
1988
25,000
30,000
Bam earthquake
Iran
2003
35,000
Manjil Rudbar earthquake
Iran
1990
36,000
Krakatoa eruption tsunami
Indonesia
1883
66,000
Ancash earthquake
Peru
1970
69,197
Sichuan earthquake
China
2008
86,000
Kashmir earthquake
Pakistan
2005
100,000
Tsunami
Messina, Italy
1908
105,000
Great Kanto earthquake
Japan
1923
Indian Ocean tsunami
Indian Ocean
2004
Tangshan earthquake
China
1976
230,000
245,000
Impacts over time
• A simplified version of Park’s hazard response model is shown
below
• Different hazard events have different impacts, shown by the
speed of the drop in quality of life, the duration of the decline,
and the speed and nature of recovery.
• The differences in the 3 lines might be related to type of
hazard, degree of preparedness, speed of the relief effort and
the nature of recovery and rebuilding.
4. Response to tectonic hazards
• People cope with natural
hazards in very different ways
• The chosen ways are often
related to wealth and access
to technology
• Humans do have a capacity to
ignore or seriously
underestimate risk, even when
it seems obvious to others
• Often it may seem obvious that
people should move out of
harms way, but in reality this
may be impossible.
Do nothing
(ignore
the risk)
Move to a
safer
location
Attempt
to prevent
the hazard
Adapt
lifestyle to
the hazard
Hazard modification
• Several different approaches can be taken to reduce the impacts of
tectonic hazards:
Modify the
event
(hazard
mitigation)
Modify human
vulnerability
Modify the
loss
Tsunami
Coastal defences
and engineering
•Warming and prediction systems
•Coastal zone management and
landuse planning
•Provision of emergency kits
Earthquakes
Not possible
•Ground shaking and liquefaction
risk mapping
•Aseismic buildings
•Earthquake education and drills
•Prediction not possible
Volcanoes
Lava diversion
•Monitoring, prediction warning
and evacuation systems
•Hazard mapping e.g. lahar risk
•Education
•Shelters
Loss modification
involves immediate
rescue efforts,
followed by relief
efforts which focus
on food, shelter,
water and
sanitation.
Insurance can help
recovery.
Long term
reconstruction is
needed.
The hazard management cycle
• Successful hazard
management involves a cycle
(see diagram) which focuses
on the 3 types of modification
from the previous slide.
• A focus on modifying loss only,
will not improve survival
chances when the next hazard
strikes
• Long before a natural hazard
event, there needs to be a
focus on mitigation and
prevention (if possible) as well
as human preparedness.