Tectonic Hazards

Question 1

Radioactive decay of…

Answer 1

Isotopes such as uranium-238 in the Earth’s core and mantle generate huge amounts of heat, which flows towards the Earth’s surface. The interior of the Earth is therefore dynamic.
Most tectonic hazards occur at or near tectonic plates boundaries.
These represent the locations of ascending and descending arms of mantle convection cells.

Question 2

Global distribution of tectonic hazards

Answer 2

Most earthquakes occur at, or close to plate boundaries. Some plate boundaries earthquakes cause a secondary tectonic hazard, tsunami.
Plate boundary type depends on:
Motion (how plates are moving)
Plate type (oceanic vs continental.)
Some volcanic eruptions are described as ‘intra plate.’ At these locations:
Isolated plumes of convicting heat, called mantle plumes, rise towards the surface generating volcanoes.
A mantle plume is stationary but the tectonic above moves slowly over it.
This produces a chain of volcanic islands.

Question 3

Divergent

Answer 3

Oceanic-oceanic - mid Atlantic ridge at Iceland. Riding convection currents bring magma to the surface resulting in small, basaltic eruptions.
Continent-continent- African rift valley. Caused by a geologically recent mantle plume splitting a continental plate to create a new ocean basin. Basaltic volcanoes and minor earthquakes.

Question 4

Convergent

Answer 4

Continent- continent- - Himalaya. Creates a mountain belt as the landmass crumples. Infrequent, major earthquakes.
Oceanic-oceanic- Aleutian Island, Alaska. One oceanic plate is subducted beneath another, generating frequent earthquakes and a curving (arc) of chain volcanic islands.
Oceanic-continent- Andean mountains. Creates a subduction zone, with a volcanic mountain range, frequent large earthquakes and violent eruptions.

Question 5

Conservative

Answer 5

Oceanic-continent- San Andreas Fault. Plates slide past each other. Frequent, shallow earthquakes but no volcanic activity.

Question 6

Earthquakes can occur..

Answer 6

In mid plate settings, usually associated with major ancient fault lines being re-activated by tectonic stress.
For example, the New Madrid Seismic Zone on the Mississippi River generated earthquakes of up to 7.5 magnitude.

Question 7

Theories of plate motion

Answer 7

Plates move at a speed of 2-5cm per year.
Wegener’s continental drift hypothesis 1912. This said that the continents were once joined.
Holmes 1930s. Earth’s radioactive heat was the driving force of mantle convection.
The discovery in 1960 of the asthenosphere.
The discovery in 1960s of magnetic stripes in the oceanic crust of the sea bed; they are palaeomagnetic, signals from past reversals of the Earth’s magnetic field and prove that new oceanic crust is created by the process of sea-floor spreading.
The recognition of transform faults by Tuzo Wilson in 1965.

Question 8

constructive margins

Answer 8

Mantle convection forces plates apart at constructive plate margins.
Tensional forces open cracks and faults between the two plates.
These create pathways for magma to move towards the surface and erupt, creating new oceanic plate.
Eruptions are small and effusive in character.
Earthquakes are shallow and have low magnitudes.

Question 9

Destructive margins and subduction zones

Answer 9

Mantle convection pulls oceanic plates apart, creating fracture zones.
Cold, dense oceanic plate is subducted beneath less dense continental plate (slab pull.)
Earthquakes at subduction zones occur at a range of focal depths, from 10km to 400km, following the line of the subducting plate. This is called the Benioff Zone and it can yield earthquakes up to a magnitude of 9.0.
The descending plate begins to melt at a depth by a process called wet partial melting. This generates magma which erupts with an explosive force.

Question 10

Collision zones

Answer 10

As both continental plates have the same density, subduction isn’t possible.
Instead, both plates have crumpled, creating enormous tectonic uplift, in the form of mountains.
Eruptions are very rare, as magma cools and solidifies beneath the surface.
They can generate shallow, high magnitude earthquakes.

Question 11

Transform zones

Answer 11

California. Creates frequent tectonic activity.
They have a shallow focal depth, meaning high magnitude.
Volcanic activity is absent.

Question 12

Causes of Earthquakes

Answer 12

They are a sudden release of stored energy. As plates attempt to move past each other along fault lines, they stick. This allows strain to build up over time and the plates are places under increasing stress.
Earthquakes are generated because of sudden release of stress (called stick-slip behavior.)
Generates 3 types of seismic waves:
P waves- fastest. Arrive first and cause the least damage.
S waves- they shake the ground violently.
L laves- they only travel across the surface. They have a large amplitude and cause significant damage.

Question 13

Secondary hazards (earthquakes)

Answer 13

Landslides. Accounted for 30% of deaths in the 1008 Sichuan and 2005 Kashmir earthquakes.
Liquefaction affects ground which consists of loose sediment. Intense shaking compacts the loose sediment together, forcing water between the sediment out and upwards. They can cause buildings to sinks and often collapse.

Question 14

Volcanic hazards

Answer 14

Lava flow- this can extend several km from the volcanic vents. Can flow at up to 40kmh.
Pyroclastic flow- very large, dense clouds of hot ash and gas at temperatures of up to 600 degrees.
Ash fall- ash particles and larger tephra particles can blanket huge areas, killing vegetation, collapsing buildings and poisoning water courses.
Gas eruption- the eruption of carbon dioxide and sulphur dioxide, which can poison people and animals/
Lahar- volcanic mudflows which occur when rainfall mobilises volcanic ash. They had travel at high speeds.
Jokulhlaup- devastating floods caused when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of water meltwater. Common in Iceland.

Question 15

Only composite volcanoes…

Answer 15

Found at destructive plate margins represent a significant tectonic hazard. These eruptions often have lava flows, pyroclastic flows, lahars and extensive ash and tephra fall that can affect areas up to 30 km from the volcanic vent.

Question 16

Tsunamis

Answer 16

Can be generated by landslides and even eruptions of volcanic islands.
Most are generated by sub-marine earthquakes at subduction zones.
Generated when the sea bed is displaced vertically, as a result of movement along a fault line at a subduction zone.
This violent movement displaces a large volume of water in the ocean column, which then moves outwards in all directions from the point of displacement.
Usually hit the coastline in a series of waves.

Question 17

Hazard vs disaster

Answer 17

Hazards are natural events which have the potential to harm people and their property.
A disaster is a realisation of a hazard. It has to involve people.
The Deggs Model shows that a disaster occurs at the intersection of a hazard and a vulnerable population.
A threshold level is used to determine whether the impact of an event is large enough to be considered a hazard:
10+ deaths
100+ affected
$1 million in economic loses.
The risk of a disaster rises if the magnitude rises. Similarly, if vulnerability rises then so does risk.

Question 18

Resilience

Answer 18

Some communities have a high capacity to cope and therefore a high resilience. This means they can reduce the change of disasters occurring:
Have emergency evacuation
They react by helping eachother
Hazard-resistant design and land-use planning.
Haiti- magnitude of 7.0 was relatively low but the death toll has been estimated at at 160,000. Main cause was a vulnerable population.

Question 19

PAR model

Answer 19

This suggests that the socio-economic context of a hazard is important.
In poor, badly governed countries, places with rapid change and a low coping capacity, disasters are likely.
Progression of vulnerability= root causes, dynamic pressures and unsafe conditions.
These combine with natural hazards to form a disaster.

Question 20

Impacts of tectonic hazards

Answer 20

Social- deaths, injury and wider health impacts.
Economic- loss of property, business and infrastructure.
Environmental- damage or destruction of physical systems, especially eco-systems.
Economic costs in developed and emerging economies are enormous.
Deaths in developed countries are low.
Impacts of volcanic eruptions are small compared to the impacts of earthquakes/ tsunamis.

Question 21

Measuring magnitude and intensity

Answer 21

Size of a tectonic event is its magnitude.
Broadly, the larger the magnitude, the bigger the impact. This isn’t a simple relationship because of the vulnerability and capacity to cope.
Magnitude is measured using the MMS. This is an updated version of the Richter Scale. MMS measures the amount of energy released during an event.
The Mercalli scale measures the intensity of an earthquake. This older scale, measures what people actually feel during an earthquake.
Volcanic explosivity index ranges from 0-8 and is a composite index, combining eruption height, volume of the material erupted and the duration of the eruption.

Question 22

Relationship between magnitude and death toll

Answer 22

A weak one:
Some earthquakes cause serious secondary hazards.
Earthquakes hitting urban areas have a greater impact than those hitting rural areas.
Levels of development and level of preparedness are important.
Isolated places could have a higher death toll because they are harder to reach.

Question 23

Hazard profiles

Answer 23

Compare tectonic hazards. They allow a better understanding of the nature of hazards and therefore the risks associated with each.
Hazards with the following characteristics present the highest risk:
High magnitude, low frequency events.
Rapid speed of onset events with low spatial predictability.
Regional areal extent.
Major earthquakes at subduction zones and collision zones are the most dangerous tectonic hazards.

Question 24

2005 Kashmir quake

Answer 24

Magnitude of 7.6
Rapid speed of onset (no chance of evacuation)
Damage was spread over an areal extent of more than 1000km.
Afterschocks up to a magnitude of 6.4
87,000 died
2.8 million displaced
17,000 schools and 800 heath centres destroyed
Numerous factors, including poverty, poor building construction, geology and terrain help to explain the impact. Most significant:
Frequency- no collective memory.
Spatial predictability (in a seismic gap ,which should have been acted upon.)

Question 25

Development and governance

Answer 25

Some relationship between death toll and HDI, with a lower HDi resulting in higher death tolls.
Other factors such as population density, duration of ground shaking, secondary hazards and response are also important.
Generally, low levels of development increases risk by increasing vulnerability.

Question 26

Factors increasing risk

Answer 26

Population growth 
Urbanisation and urban sprawl
Environmental degradation 
Loss of community memory 
Very young or very old population
Ageing, inadequate, infrastructure

Question 27

Factors mitigating risk

Answer 27

Warning and emergency response systems
Economic wealth 
Government disaster-assistance programmes
Insurance 
Community initatives
Scientific understanding 
Hazard engineering

Question 28

In location with low HDI, vulnerability is usually high because:

Answer 28

People lack basic needs
Much housing is informally built
Access to healthcare is poor and disease is common
Education levels are lower
Many low income groups lack a safety net, so have few resources to help recover from a hazard.

Question 29

In Nepal 2015…

Answer 29

40% of families live below the poverty line
90% depend on subsistence farming
40% of population exhibit stunting as a result of malnutrition
Only 20-40% of adults are literate.

Question 30

Governance

Answer 30

This is the process by which a country or region is run.
Good governance suggests that national and local government are effective in keeping people safe, healthy and educated.
The effectiveness of governance varies enormously and has a significant impact on coping capacity and resilience.

Question 31

Aspects of governance and disaster vulnerability

Answer 31

Meeting basic needs - when food / water supplies are met, the physical population is more able to cope.
Planning- land-use planning can reduce the risk by preventing habitation on high risk areas.
Environmental management- secondary hazards can be made worse bu deforestation.
Preparedness- education and community preparation programmes raise awareness and teach people how to prepare.
Corruption

Question 32

National disaster management agencies

Answer 32

Most countries have these.
e.g FEMA in the USA.
These can increase resilience to hazards and reduce the impacts of disasters.
PHIVOLCS in the Philippines are under-funded and resourced.
Low levels of corruption in developing countries mean that building codes are often ignored and construction is allowed in inappropriate places.

Question 33

Geographical factors

Answer 33

Population density - highly populated areas may be harder to evacuate.
Degree of urbanisation- higher concentration of at risk people.
Isolation and accessibility- this can slow rescue relief efforts.
Urban areas often have more assets than rural areas. These include hospitals, emergency relief services and transport connections, which increases resilience. However, higher population density, may mean more people affected.

Question 34

In developed countries, major death tolls of tectonic hazards are rare because:

Answer 34

Advanced and widespread insurance, allowing people to recover
Government run preparations, such as Japan’s disaster Prevention day on 1 September
Sophisticated monitoring of volcanoes and defences
Regulated local planning systems and building codes to ensure that buildings can withstand tectonic hazards.

Question 35

Tectonic disaster trends

Answer 35

Deaths have fallen over time because of better response management, preparation and prediction.
Number of reported disasters rose than stabilised.
Number of people affected continues to grow.
Earthquake deaths are variable, fewer than 1000 deaths worldwide in 2012 / 2014 yet more than 200,000 in 2010/ 2004.
Economic losses are increasing.
Volcanic disasters are much less frequent than earthquakes and deaths from eruptions are no rare.
Only 7 eruptions since 1980 have killed more than 100 people.

Question 36

Mt. Merapi

Answer 36

Indonesia.

130,000 affected but only 300 deaths.

Question 37

Mega disasters

Answer 37

Very large tectonic disasters account for most deaths.
Haiti quake accounts for 50% of earthquake deaths between 2005-2015.
They are characterised by impacts extending beyond the country immediately affected.
The 2011 tsunami in Japan showed how the globalised inter-dependent world economy could be affected.

Question 38

Multiple hazard zones

Answer 38

Include:
California, Philippines, Indonesia and Japan.
These locations are:
Tectionically active and so earthquakes are common
Geology young, so prone to landslides
Often on major storm tracks
Suffer from global climate perturbations.

Question 39

Mount Pinatubo

Answer 39

1991. The Philippines
      Heavy rainfall from Typhoon Yunga mobilised volcanic ash into destructive lahars.
      This was effectively predicted and evacuated, so death toll was limited to about 850.

Question 40

Prediction and forecasting

Answer 40

Depends on the technology in place.
Tsunami monitoring was not present in the Indian ocean of 2004, so there was no way of warning people.
In many developing countries, volcano monitoring isn’t as good, because of the cost of the technology.

Question 41

Hazard management

Answer 41

The hazard management cycle illustrates the different stages of managing hazards, in an attempt to reduce the scale of a disaster.
Preparedness- community education and resilience building.
Response- immediate help
Recovery- rebuilding infrastructure and services, rehabilitating injured people
Mitigation- acting to reduce the scale of the next disaster

Question 42

Disaster modification

Answer 42

Disasters can be managed by modifying the impacts. This can be done in 3 ways:
Modifying event,
Modifying vulnerability,
Modifying loss.

Question 43

Modify the event

Answer 43

Relies on technology and planning systems and can be high cost. Less likely to be used in developing countries.
Land use zoning:
Low cost, removes people from at risk areas.
Prevents economic development, requires strict and enforced planning.
Aseismic buildings:
Prevents collapse, so protects both people and property.
This is high cost and older buildings/ low income homes are rarely protected.
Tsunami defences:
Dramatically reduces damage, provides a sense of security.
Can be overtopped, very expensive and ugly.
Lava diversion:
Diverts lava out of harms way, relatively low cost.
Only works for low VEI bsaltic lava.

Question 44

Modify the vulnerability

Answer 44

Means increasing the resilience of a community to increase their capacity to cope. Prediction, warning and evacuation are used to move people out of harm’s way.
Hi tec monitoring:
Predicting an eruption is possible, warnings and evacuation saves lives.
Costly, may suffer from ‘cry wolf syndrome,’ doesn’t prevent property damage.
Community preparedness/ education:
Low cost and can save lives.
Doesn’t prevent property damage, harder to implement in isolated, rural areas.
Adaption (moving people out of harm’s way:)
Would save both lives and property.
High population densities prevents this and it disrupts people’s traditional homes/ traditions.

Question 45

Modify the loss

Answer 45

This is picking up the pieces after a disaster has occurred. In developing countries this is often the main management strategy.
Short term, emergency aid:
Reduces death toll
High cost, emergency services are limited.
Long term aid:
Reconstruction can build in resilience.
Very high cost, needs are quickly forgotten.
Insurance:
Allows people to recover economically.
Doesn’t save lives, few people in the developing world have insurance

Question 46

2004 Asian tsunami

Answer 46

14 countries affected.

Economic losses and deaths in Indonesia, Thailand, Sri Lanka and Somalia.

Question 47

2011 Japanese tsunami

Answer 47

Only Japan directly affected but the economic impacts had global consequences.
Disruption to ports, factories and power supplies had impacts for the global-car production chain.

Question 48

2011 Iceland eruption

Answer 48

Over 20 European countries affected.

Ash cloud affected air travel, with over 100,00 cancelled flights costing over £1 billion in losses.