A2 CAMBRIDGE GEOGRAPHY: HAZARDOUS ENVIRONMENTS - HAZARDS RESULTING FROM TECTONIC PROCESSES. It contains: earthquakes, volcanoes, tsunamis.

1. A2 GEOGRAPHY
HAZARDOUS ENVIRONMENTS
9.1 HAZARDS RESULTING
FROM TECTONIC PROCESSES
ANIMATED PRESENTATION
- FOR ANIMATION: DOWNLOAD AND SLIDESHOW MODE ONLY -

2. EARTHQUAKES AND VOLCANOES
Tectonic hazards include:
SEISMIC ACTIVITY
(EARTHQUAKES)
VOLCANOES
TSUNAMI
Most of the world’s
earthquakes occur in clearly
defined linear patterns.
These linear chains generally
follow plate boundaries.

3. GLOBAL DISTRIBUTION OF
EARTHQUAKES AND VOLCANOES

4. EARTHQUAKES
Broad belts of
earthquakes are
associated with
subduction zones, where
a dense ocean plate
plunges beneath a less
dense continental plate.
Narrower belts of
earthquakes are
associated with
constructive plate
margins, where new
material is formed, and
plates are moving apart.

5. EARTHQUAKES
Collision boundaries, such as
in the Himalayas, are also
associated with broad belts of
earthquakes, whereas
conservative plate
boundaries, such as
California’s San Andreas fault
line, give a relatively narrow
belt of earthquakes (this can
still be over 100 km wide).
There are occurrences of
earthquakes related to
isolated plumes of tectonic
activity, known as hotspots.

6. TYPICAL MISTAKE
Most earthquakes are associated with plate boundaries and
tectonic activity, many earthquakes occur at great distances
from plate boundaries and are not readily explained by
tectonic activity.

7. VOLCANOES
Most volcanoes are found at plate boundaries, with some
exceptions, such as the volcanoes of Hawaii, which occur over
hot spots (isolated plumes of rising magma).
About three-quarters of the Earth’s 550 historically active
volcanoes lie along the Pacific Ring of Fire.
At subduction zones volcanoes produce more viscous lava,
and tend to erupt explosively and produce much ash.
By contrast, volcanoes that are found at mid-ocean ridges or
hot spots tend to produce relatively fluid basaltic lava, as in
the case of Iceland and Hawaii.

9. TSUNAMIS
Up to 90% of the world‘s
tsunamis occur in the
Pacific Ocean.
This is because they are
associated with subduction
zones, most of which are
found in the Pacific.
Tsunamis are generally
caused by earthquakes,
usually in subduction
zones, but can be caused by
volcanoes (like Krakatoa in
1883), and landslides (like
Alaska in 1964).

10. EARTHQUAKES AND
RESULTANT HAZARDS

11. EARTHQUAKES: HAZARDS AND IMPACTS
HAZARDS
Primary hazards
• Ground shaking
• Surface faulting
Secondary hazards
• Ground failure and soil liquefaction
• Landslides and rockfalls
• Debris flow and mud flow
• Tsunamis

12. EARTHQUAKES: HAZARDS AND IMPACTS
IMPACTS
• Loss of life
• Loss of livelihood
• Total or partial destruction of building structure
• Interruption of water supplies
• Breakage of sewage disposal systems
• Loss of public utilities such as electricity or gas
• Floods from collapsed dams
• Release of hazardous material
• Fires
• Spread of chronic illness

13. FACTORS AFFECTING
EARTHQUAKE DAMAGE
The extent of earthquake damage is influenced by:
- The strength and depth of earthquake and number of aftershocks
- Population density
- The type of buildings
- The time of day
- The distance from the centre (epicentre) of the earthquake
- The type of rocks and sediments
- Secondary hazards
- Economic development
Most earthquakes occur with little advance warning. Most problems
are associated with damage to buildings, structures and transport.

14. WAYS OF PREDICTING AND MONITORING
These include measurements of:
- Small-scale uplift, subsidence or ground tilt
- Changes in rock stress
- Microearthquake activity (clusters of small quakes)
- Anomalies in the Earth’s magnetic field
- Changes in Radon gas concentration
- Changes in electrical resistivity of rocks

15. TSUNAMI WARNING SYSTEMS
At present it is
impossible to
predict precisely
where and when
a tsunami will
happen.
In most cases it
is only possible
to raise the
alarm once a
tsunami has
started (early
warning system).

16. DEEP TSUNAMI WARNING SYSTEMS
Deep-ocean tsunami
detection buoys are one of
two types of instrument used
by the Bureau of
Meteorology (Bureau) to
confirm the existence of
tsunami waves generated by
undersea earthquakes. These
buoys observe and record
changes in sea level out in
the deep ocean.
This enhances the capability
for early detection and real
time reporting of tsunamis
before they reach land.

17. DEEP TSUNAMI
WARNING SYSTEMS
Deep-ocean tsunami detection
buoy technology was initially
developed in the United States of
America by the Pacific Marine
Environmental Laboratory. These
systems are capable of measuring
sea-level changes of less than a
millimetre in the deep ocean.
Two-way communication
between the tsunami buoy and
the tsunami warning centre
means that the buoy can be
controlled remotely.

18. VOLCANIC HAZARDS

19. VOLCANIC HAZARDS
Volcanic hazards can be divided into six main categories:
Lava flows
Ballistic and tephra clouds
Pyroclastic flows and ash fallout
Gases and acid rain
Lahars (mud flows)
Glacier bursts (Jokulhlaups)

21. LAVA FLOWS
Lava flows are the least
hazardous of all
processes in volcanic
eruptions.
How far a lava flow
travels depends on the
flows temperature, silica
content, extrusion rate,
and slope of the land.
A cold lava flow will not
travel far and neither
will one that has a high
silica content.

22. BALLISTIC AND TEPHRA CLOUDS
Tephra falls and Ballistic
Projectiles formed on Land.
Tephra consists of
pyroclastic fragments of
any size and origin.
It is a synonym for
"pyroclastic material.“
Tephra ranges in size from
ash (<2 mm) to lapilli (2-64
mm) to blocks and bombs
(>64 mm).

23. PYROCLASTIC FLOWS
Pyroclastic flows consists of
particles that have been ejected
from vents and have travelled
through the atmosphere before
falling to earth or into water.
Transport of pyroclastic fallout
material is by ballistic trajectory
and by turbulent suspension.
Energy is supplied initially to
fragments by the eruption and
later by wind.
Elutriation is a process for separating particles
based on their size, shape and density, using a
stream of gas or liquid flowing in a direction
opposite to the direction of sedimentation.
A pyroclastic flows is a fast-moving cloud
of extremely hot gas, ash and rock
fragments, which can reach temperatures of
about 1000 degrees Celsius and travel at
speeds of up to 700km/h.
A nuee ardente is a mass of hot gas,
superheated steam and volcanic dust that
travels down the side of a volcano as a
“glowing avalanche” following a volcanic
eruption.

24. ASH FALLOUT
Fallout ash can also
be derived from
elutriation of ash
the boils up from
pyroclastic flows as
they travel across
the land.
Pyroclastic material
that falls on land is
"subaerial fallout,"
and that falling into
water is subaqueous
fallout.

25. GASES AND ACID RAIN
Acid rain is caused by a
chemical reaction that
begins when compounds
like sulphur dioxide and
nitrogen oxides are
released into the air.
These substances can
rise very high into the
atmosphere, where they
mix and react with
water, oxygen, and other
chemicals to form more
acidic pollutants, known
as acid rain.

26. LAHARS (MUDFLOWS)
A lahar is a type of
mudflow or debris flow
composed of a slurry of
pyroclastic material,
rocky debris, and water.
The material flows down
from a volcano, typically
along a river valley.
Lahars are extremely
destructive: they can flow
tens of metres per
second, be 140 metres
deep, and large flows can
destroy any structures in
their path.

27. GLACIER
BURSTS
A glacial lake outburst flood is
a type of outburst flood
occurring when water dammed
by a glacier or a moraine is
released.
When a marginal lake bursts, it
may also be called a marginal
lake drainage.
When a sub-glacial lake bursts,
it may be called a jökulhlaup.
Jokulhlaups in Iceland
The term "jokulhlaup" is derived from
Icelandic and refers to an outburst flood
event of glacial origin. Jokulhlaups can start
when cavities in or under the glacier rapidly
release quantities of water at unpredictable
times. Some jokulhlaups are small and others
such as the November 1996 event in Iceland
are cataclysmic events and truly worthy
examples of mass wasting.

28. HAZARDS ASSOCIATED WITH
VOLCANIC ACTIVITY
DIRECT HAZARDS
(PRIMARY HAZARDS)
INDIRECT HAZARDS
(SECONDARY HAZARDS)
SOCIO-ECONOMIC
IMPACTS
Pyroclastic flows
Volcanic bombs
Lava flows
Ash fallout
Volcanic gases
Nuees ardentes
Earthquakes
Atmospheric ash fall out
Landslides
Tsunamis
Acid rainfall
Lahars (mudflows)
Destruction of settlements
Loss of life
Loss of farmland and forests
Destruction of
infrastructure – roads,
airstrips and port facilities
Disruption of
communications

29. EXPERT TIP
It is a good idea to have contrasting case studies
of volcanoes – one MEDC and one LEDC – to bring
out differences in impact, management, land-use.

30. PREDICTING VOLCANOES
Volcanoes are easier to predict than earthquakes because there
are certain signs. The main ways of predicting volcanoes
include:
- Seismometers to record swarms of tiny earthquakes that
occur as the magma rises
- Chemical sensors to measure increased sulphur levels
- Lasers to detect the physical swelling of the volcano
- Ultrasound to monitor low-frequency waves in the magma,
resulting from the surge of gas and molten rock
- Direct observation

31. FACTORS AFFECTING
THE PERCEPTION OF RISK
At an individual level there are three important influences on
an individual’s response to risk. For example:
- Experience – the more experience of environmental hazards
the greater the adjustment to the hazard
- Material well-being – those who are better off have more
choice
- Personality – is the person a leader or a follower, a risk-taker
or risk-minimiser

32. THREE CHOICES
Ultimately there are three choices:
- do nothing and accept the hazard;
- adjust to the situation of living in a hazardous environment;
- leave the area.
It is the adjustment to the hazard that we are interested in. The
level of adjustment will depend, in part, upon assessing the
risks caused by the hazard. This includes:
- Identification of the hazards
- Estimation of the risk (probability) of the environmental
hazard
- Evaluation of the cost (loss) caused by the environmental
hazard