Transcript TECTONIC ACTIVITY and HAZARDS - School

TECTONIC ACTIVITY and HAZARDS
Tectonic Activity and Hazards
Cameron Dunn
Chief Examiner
TECTONIC ACTIVITY and HAZARDS
1.The specification
There are four themes to cover in the spec*:
• 1.1.Tectonic activity and causes
• 1.2.Tectonic hazard physical impacts
• 1.3.Tectonic hazard human impacts
• 1.4.Response to tectonic hazards
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2.Key differences compared to Legacy Spec B
• The spec is narrower than Spec B Unit 5 Hazard
– this is just tectonics
• There is a strong focus on causes and
understanding plate motion and boundaries
• The tectonic landscapes element (1.2) is new
• Human impacts (1.3) and responses (1.4) are
similar to what many of you are used to
• A further important point is that students have
studied the distribution of hazards in Unit 1 at AS
level.
TECTONIC ACTIVITY and HAZARDS
1.The Geography of volcanoes:
 Active volcanoes recorded since October 2004
TECTONIC ACTIVITY and HAZARDS
Tectonic settings & plate margins:
Constructive:
Destructive:
Conservative:
Hotspots:
oceanic 
oceanic 

oceanic 
continental 
continental 
continental 
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Geography:
• Well known locations.
• 50% of eruptions occur around
the Pacific Rim of Fire.
• A common hazard; 82
eruptions in the last year.
• Areas of increasing human
settlement.
• Very variable hazards and
impacts.
• Key to understanding them is
to understand the generation
of magma:
MAGMA
PARTIAL MELTING
HEAT
SOURCE
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2.The range of volcanic hazards:
• Huge variation in
hazard from merely
spectacular to
devastating.
• Some volcanoes
generate a single
hazard, such as a lava
flow.
• The most dangerous
volcanoes are multiple
hazard areas.
• This presents a series
of management
challenges.
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Magma
type
Tectonic setting
Hazards
•Oceanic Hot spot (Hawaii)
•CPM (Iceland)
•Lava flow
Andesitic
•DPM (Andes)
•Island arc (Montserrat)
•Lava flow
•Ash and tephra
•Pyroclastic flow
•Lahar
•Gas emission
Rhyolitic
•Continental Hot spot (Yellowstone)
•Continent collision zone (Himalaya)
•Explosion
•Pyroclastic flow
Basaltic
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Measuring explosivity:
• 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
TECTONIC ACTIVITY and HAZARDS
Explaining explosivity:
Magma
type
Eruption
temperature
Gas content
Viscosity
SiO2 content
Basaltic
(basic)
1100°C
LOW
LOW
(runny)
50%
Andesitic
1000 °C
MODERATE
MODERATE
60%
800 °C
HIGH
HIGH
(sticky)
70%
(intermediate)
Rhyolitic
(felsic)
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Magma type & volcano morphology
• 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.
TECTONIC ACTIVITY and HAZARDS
3.Some case studies: KILAUEA, Hawaii
• Mantle convection
plume (hot spot) = heat
source.
• Partial melting of the
upper mantle material
(peridotite) occurs.
• This yields basaltic lava
• Low gas content, low
silica content, low
viscosity, high
temperature.
• The hot spot is stationary,
oceanic plate moves over
it, forming an island
chain.
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NYIRAGONGO, Democratic Republic of
Congo
• Unusual tectonic setting; a
continental CPM
• Erupting basaltic magma
• Unusually high sulphur
emissions and very high
temperature, low silica lava.
Flows move at 60 km/h +
• Erupted in 1977 (100-1000
deaths) and again in 2002 (45
deaths; possibly 100,000
homeless)
• Up to 500,000 potentially at
risk.
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SOUFRIERE HILLS, Montserrat
• An island arc DPM.
• Two oceanic plates in collision.
• Subduction of one tectonic plate
occurs
• Note that both plates are made
of basalt.
• Explosive eruption
characterised by pyroclastic
flows.
• The 1995-97 eruption caused
over half of the island to be
abandoned due to pyroclastic
flow risk
TECTONIC ACTIVITY and HAZARDS
Why is Soufriere Hills explosive?
•Water within the oceanic plate, lowers the melting temperature of some minerals
in the subducting plate.
•These minerals rise away from the unmelted part – a wet partial melt.
•The melted portion has a high silica and high gas content.
•As the magma nears the surface, confining pressure drops, the dissolved gas in
the magma expands (decompression). This blasts material out of the vent.
TECTONIC ACTIVITY and HAZARDS
YELLOWSTONE CALDERA, USA
• Tectonic setting is a
continental hot spot in northwest USA.
• Hot spot causes in situ melting
of the continental plate.
• As this is granitic, very viscous,
low temperature, high gas
content rhyolitic magma is
produced.
• The North American
continental plate moves over
the hot spot at 2-4cm/yr.
TECTONIC ACTIVITY and HAZARDS
• The caldera (huge crater) at Yellowstone is 75 x 45 km wide
TECTONIC ACTIVITY and HAZARDS
• Ash and tephra could
cover an area of 30,000
km2
• Short-term climate
change likely
• Huge potential impacts
on ecosystems, people
and economies
TECTONIC ACTIVITY and HAZARDS
Summary:
• Volcanic impacts are
linked to tectonic setting
• Understanding the
generation of magma is
key to understanding the
hazards
• Impacts are a result of
magma viscosity (gas &
silica content,
temperature)
• Fortunately, the more
viscous the magma, the
rarer the eruption.
TECTONIC ACTIVITY and HAZARDS
Tectonic landscapes
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Using models and concepts
• See notes
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A useful structure
• The Disaster Risk
Management
Cycle, or Hazard
Management
Cycle
• Useful concept for
students
Aseismic
Design
Tsunami
warning
U.N. emergency
response
TECTONIC ACTIVITY and HAZARDS
MITIGATION – building in earthquake zones
• Hazard resistant
design
• Long term policy
• High cost
• Requires legal
codes, inspection
and review
TECTONIC ACTIVITY and HAZARDS
The hi-tech solution:
• Costly
• 50-80% of
new-build
cost to retrofit
• Adds 10-25%
to new-build
cost
Crossbracing
resists
lateral
forces
Tuned mass
damper reduces
sway / vibration
Laminated or
similarly
strengthened
glass
Fluid
dampers
(shock
absorbers)
can be
installed
Pile
foundations
extend to
rockhead
Base isolation allows
foundation movement,
not building failure
TECTONIC ACTIVITY and HAZARDS
• Taipei 101
• World’s tallest building, and world’s largest
tuned mass damper at 730 tons.
• 8 massive vertical columns add rigidity, whilst
an external steel frame allows flex.
• 380, 80m concrete piles support the structure
from below
TECTONIC ACTIVITY and HAZARDS
• This 6 storey newbuild in Pakistan
breaks every rule in
the book:
• No cross bracing
• Brick in-fill walls not tied to
the frame
• Complex masses
• Low quality materials
TECTONIC ACTIVITY and HAZARDS
Options for the developing world:
• Up to 50% of people in
the developing world
live in adobe brick
homes
• The failure rate during
earthquakes is up to
90%
• Intermediate
technology and
education can save
lives.
http://www.world-housing.net/
TECTONIC ACTIVITY and HAZARDS
• Visual instructions for reinforcing
adobe buildings using groundplans, concrete ring foundations,
and flexible vertical supports
See also guidelines for
rebuilding in Kashmir from http://www.erra.gov.pk
TECTONIC ACTIVITY and HAZARDS
PREDICTION & EVACUATION
• Response to the tsunami
hazard, Okushiri Island, Japan
• Devastating tsunami struck in
1993, killing 198 and destroying
30% of homes
• Cause was a 7.8 earthquake,
generating waves of up to 25m
• Warning was at most 2-3
minutes from the earthquake
TECTONIC ACTIVITY and HAZARDS
http://nctr.pmel.noaa.gov/
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Japan has spent US$1.3 billion rebuilding
the island (population 3700), and renewing
its tsunami defences:
Nine mile long, 12m high sea wall
Tsunami evacuation platforms
Each house and business on Okushiri
Sluice gates
has an automated tsunami alarm,
close over
linked to the ocean detection system.
river mouths
TECTONIC ACTIVITY and HAZARDS
Can the developing world benefit from the
technological fix?
• Probably not, in terms of coastal defences due to high costs
• Warning systems are being developed, but will depend on effective
information dissemination and evacuation systems if they are to be
successful
• The technology to warn of tsunami is well-developed.
• The PTWC (Pacific Tsunami Warning Centre) did issue a tsunami warning 15
minutes after the first fault motion off Sumatra in 2004, 1 minute
before the first waves struck the island.
TECTONIC ACTIVITY and HAZARDS
(See the flyer in your pack for further details)
www.gitews.org, and the BBC website has a
good explanation of how tsunami warning systems
work.
TECTONIC ACTIVITY and HAZARDS
Indian Ocean Tsunami Warning and
Mitigation System (IOTWS)
• Co-ordinated by
UNESCO
• Aid from MEDCs
• The system went ‘live’ in
June 2006
• 3 DART buoys currently
in place, plus over 20
seismic stations, with
more planned.
http://ioc3.unesco.org/indotsunami/
TECTONIC ACTIVITY and HAZARDS
The easy bit?
The hard part?
US$200 million cost
$25 million annually to run.
•
Political co-operation
needed.
•
Technical expertise.
•
Dissemination system
•
Warning system
•
Evacuation routes and
safe-havens
•
Education of population
•
Planning / Zoning to
reduce economic loss
“A timely 100 percent accurate
and precise warning will
not provide any protection,
if people do not know how
to respond to the
emergency”
(UNESCO D-G, 2006)
TECTONIC ACTIVITY and HAZARDS
Why was the Kashmir death toll so high?
• 74,500 fatalities *, including
18,000 children
• 106,000 people injured
• 780,000 buildings destroyed
or uninhabitable
• 10,000 of 11,500 schools
collapsed
• 3.5 million people rendered
homeless
Deadliest earthquakes since 1900
1976 Tangshan, China 255,000.
2004 Sumatra, Indonesia 230,000
1920 Ningxia-Gansu, China 200,000
1927 Tsinghai, China 200,000
1923 Kanto, Japan 143,000
1948 Ashgabat, Turkmenistan 110,000
2005 Kashmir, Pakistan 80,000
*The official figure is 80,000, but some
experts suggest 100,000
TECTONIC ACTIVITY and HAZARDS
• Kashmir was a classic
‘seismic gap’
• Lack of experience and
expectation
• Virtually all buildings were
destroyed; almost none were
EQ proof.
• Around 2400 landslides
occurred; killing perhaps
24,000
• Most children were at school
(Saturday morning)
• Landslides hampered relief
efforts, as did terrain and
remoteness
Source: Prof David Petley,
University of Durham
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The historic town of Balakot has been effectively obliterated by the earthquake.
The city of Muzaffarabad
Source: Prof David Petley,
University of Durham
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• Kashmir fits the saying
‘earthquakes don’t kill,
buildings do’
• Up to 50% of people in the
developing world live in adobe
brick homes: the failure rate
during earthquakes is up to 90%
• This 6 storey new-build in
Pakistan breaks every rule in the
book:
• No cross bracing
• Brick in-fill walls not tied to the
frame
• Complex masses
• Low quality materials
TECTONIC ACTIVITY and HAZARDS
•
The rebuilding effort in Kashmir
is co-ordinated by the ERRA *
http://www.erra.gov.pk
• It has a number of key aims:
1- Zoning the re-build area
to identify RISK
2- Micro-zoning urban
areas, such as
Muzaffarabad, to further
identify risk
3- Education on building
reconstruction to ensure
rebuilds are safe
(see example)
*Earthquake Reconstruction and Rehabilitation Authority)