6GEO4 Unit 4 Tectonic Activity and Hazards

1
6GEO4 Unit 4 Tectonic Activity and Hazards
2
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.

3
CONTENTS

• Tectonic activity and causes
• Tectonic hazards physical impacts
• Tectonic hazards human impacts
• Response to tectonic hazards

Click on the information icon to jump
to that section. Click on the home button
to return to this contents page
4
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
5
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.

6
Earths 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

7
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.

8
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.

9
Magma generation

• Magma, molten rock in the earths 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

10
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

11
Earthquakes

• Earthquakes are a very common, sudden release of
  energy that generate seismic waves
• Most occur along faults (cracks in the earths
  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.

12
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

13
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)

14
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.

15
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

16
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

17
Earthquakes and faults

• Tectonic movements and movements along faults
  (which generate earthquakes) also produce
  distinctive landforms and relief

Note diagram not to scale
18
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

19
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).

20

• 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

21
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

22
Impacts over time

• A simplified version of Parks 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.

23
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.

24
Hazard modification

• Several different approaches can be taken to
  reduce the impacts of tectonic hazards

25
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.