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Global Distribution of tectonic
hazards
 Tectonics hazards include earthquakes, volcanoes and
tsunamis.
 Most of the wor...
Global distribution of tectonic
hazards
Earthquakes
Earthquakes
 What is an earthquake?
An Earthquake is a series of
vibrations or seismic waves which
originate from the foc...
Earthquakes
 Following an earthquake two types of body waves (waves within the Earth’s interior) occur.
 The first kind ...
Andrija Mahorovicic
Discontinuity
 Mohorovičić discontinuity, often called Moho, is the
boundary between Earth's crust an...
Khan Academy video lecture on
Andrija Mohorovicic
Shadow Zones
 Later geologists found a shadow zone, an area between 105° and 142°
from the source of the earthquake, with...
The Richter and Mercalli
Scales
Comparison of scales
Richter Scale Mercalli Scale
Measures: The energy released by the
earthquake.
The effects caused by t...
Factors affecting
earthquake damage
 Strength and depth of earthquake + Number of aftershocks:
the stronger the earthquak...
Resultant hazards of
earthquakes
 Most earthquakes occur with little if any advance warning. Some places, such as Califor...
Earthquakes and human
activities
 Human activities can trigger earthquakes, or
alter the magnitude and frequency of
earth...
Disposal of liquid waste
 Water that is salty or polluted by chemicals needs to be disposed of in a manner that
prevents ...
Underground Nuclear
Testing
 Underground nuclear
testing has triggered
earthquakes in a number of
places. In 1968 testing...
Increased crustal loading
 Earthquakes can be caused by adding increased
loads on previously stable land surfaces. For
ex...
What should people do
about earthquakes
 People deal with earthquakes in a
number of ways. These include:
1. Do nothing a...
Volcanoes
A volcano is an opening
in the Earth’s crust
where magma – a
mixture of red-hot liquid
rock, mineral crystals,
r...
Types of Volcanoes
 There are two main types of Volcanoes:
1. Shield,
2. Cone
 The shape of a volcano depends on the typ...
Types of Volcanoes:
Shield
 Shield volcanoes are low with gently
sloping sides and are formed from layers of
lava.
 Erup...
Types of volcanoes: Cone
 Acid lava that flows from cone or
dome volcanoes is much more
viscous than lava which flows fro...
Volcanoes are classified in a number of ways.
These include the type of flow, type of eruption
and level of activity….
 A...
Types of volcanic
eruptions
 Volcanic eruptions are often thought of as cataclysmic explosions that
produce vast quantiti...
Types of eruptions
Plinian Eruptions
 These are the most explosive and violent of volcanic eruptions. They
produce huge plumes of ash and ga...
Hawaiian Eruptions
 In Hawaiian Eruptions the lava is more basic and
basaltic, with low gas pressures and low silica
cont...
Strombolian eruptions
 Strombolian eruptions are named after Stromboli in
Italy.
 The effects are impressive but not par...
Types of eruptions
Icelandic lava eruptions
 Characterised by persistent
fissure eruption
 Large quantities of basaltic
...
Volcanic Hazards
 Volcanic hazards can be divided into six main
categories:
1. Lava flows
2. Ballistics and Tephra louds
...
Volcanic hazards
 As and debris falls steadily from the volcanic cloud, blanketing the ground with a deposit known as
a p...
Volcanic Hazards
Primary Hazards Secondary Hazards Socio-Economic
impacts
• Pyroclastic flows
• Volcanic bombs
• Lava flow...
Volcanic Strength
 The strength of a volcano is measured by the
Volcanic Explosive index (VEI). This is based on the
amou...
Predicting volcanoes
 Scientists are increasingly successful in predicting volcanoes. Since 1980 they have
correctly pred...
Living with a volcano
 People often choose to live in volcanic areas because they are useful in a
variety of ways…
 Some...
Secondary hazards of
tectonic events
Lahar
 One hazard that is closely associated with volcanic activity is the
lahar:
 Rain brings soot and ash back to grou...
Tsunami
 The term tsunami is
Japanese for ‘harbour
wave’
 90% of tsunamis occur in
the Pacific basin.
 They are general...
Factors affecting the
perception of risk
 At an individual level there are three important influences
upon an individuals...
Hazardous
environments resulting
from mass movements
What is mass movement?
 Mass movement can be defined as the large scale
movement of weathered material in response to gra...
Factors affecting mass
movement
 Slope of the land surface: When the slope gradient is steep, mass movement is rapid.
 W...
Shear stress and
resistance
 The likelihood of a slope failing depends on the
relative strength and resistance of the slo...
Classification of mass
movements
 Mass movements are classified in
a number of ways, including speed
of movement and the ...
Avalanches
 Avalanches are mass movements of snow and ice. Newly fallen snow may
fall off older snow, especially in winte...
Classification of
avalanches
Avalanches
 Although avalanches cannot be prevented, it is possible to reduce their impact through fences,
rakes, wedges,...
Avalanche video
Hazards resulting
from atmospheric
disturbances
Tropical storms (cyclones)
 Tropical storms bring intense rainfall and very high winds, which may in turn cause storm sur...
Conditions needed for
tropical storm formation
 Sea temperatures must be over 27° to a depth of 60m as
the warm water giv...
How are tropical storms
measured?
 Tropical storms are the most violent, damaging and frequent
hazard to affect the tropi...
Saffir-Simpson Scale
Factors affecting impact of
tropical storms
 Tropical storm paths are unpredictable, which makes effective management
of ...
Formation clip
Tropical storm
management
 Information regarding tropical storms is received
from a number of sources including…
1. Satel...
Preparing for tropical
storms
Beforethestorm
Know where your
emergency shelters are
Have disaster supplies on
hand
Protect...
Reducing vulnerability of
structures and
infrastructures
 New buildings should be designed to be wind and water
resistant...
Tornadoes
 Tornadoes are small and short-lived but highly
destructive storms. Because of their severe nature and
small si...
How tornadoes form
 Moisture, instability, lift and wind shear are the four key ingredients in
tornado formation.
 Most ...
Step by step formation
 Step 1: Like all winds and storms, tornadoes begin when the sun heats up the surface
of the land....
Ted Talk: How tornadoes
form
Press image – a play
button will show.
Click this to watch…
Tornado damage
 About a thousand tornadoes hit the USA each year with an average of 60 people dying per year from them. A...
Tornado
Fujita
damage
scale
Managing tornadoes
 The main problem with anything that could realistically stand a
chance of affecting a tornado (for e....
Sustainable
management of
hazardous
environments
Assessing and mitigating
damaging effects of mass
movements
 Landslides and other forms of mass movement are widespread a...
Hazard management, risk
assessment and
perception
 Hazard management includes a body of theory
which includes: risk, pred...
Learning to live with
Earthquakes
 Most places with a history of earthquakes have
developed plans that enable people to d...
1. Preparation
 Earthquakes killed about 1.5 million people in the 20th century and the number
of earthquakes appears to ...
2. Building design
 Increasingly, as the availability of building land is reduced, more and more people are
living in sei...
Controlling earthquakes
 In theory, by altering the fluid pressure deep
underground at the point of greatest stress
in th...
Hazardous environments
Hazardous environments
Hazardous environments
Hazardous environments
Hazardous environments
Hazardous environments
Hazardous environments
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Hazardous environments

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Hazardous environment A2 level geography CIE
Earthquakes
Volcanoes
Tornadoes
Hazards
Tectonics

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Hazardous environments

  1. 1. Global Distribution of tectonic hazards  Tectonics hazards include earthquakes, volcanoes and tsunamis.  Most of the world’s earthquakes occur in clearly defined linear patterns, generally following plate boundaries.  These linear chains can be in broad belts or narrow belts and generally are found on the ‘Pacific ring of fire’.  Broad belts of earthquakes are associated with subduction zones (where one plate is forced under the other) and collision boundaries  Narrow belts of earthquakes however are associated with constructive margins, where new material is formed and plates are moving apart.
  2. 2. Global distribution of tectonic hazards
  3. 3. Earthquakes
  4. 4. Earthquakes  What is an earthquake? An Earthquake is a series of vibrations or seismic waves which originate from the focus.  Focus: The focus is the point at which the plates release their tension or compression suddenly.  Epicentre: Marks the point of the surface of the Earth immediately above the focus of the earthquake.  A large earthquake can be preceded by smaller tremors known as foreshocks and followed by numerous aftershocks. • Aftershocks can be devastating because they damage buildings that have already been damaged by the main shock. • Seismic waves are able to travel along the surface of the Earth and through the body of the earth.
  5. 5. Earthquakes  Following an earthquake two types of body waves (waves within the Earth’s interior) occur.  The first kind are P-Waves (primary or pressure waves) which travel by compression and expansion. These waves are able to pass through all matter be it solid, liquid or gas.  The transverse S-Waves or Shear waves move in a series of oscillations at right-angles to the direction of movement. S-waves arrive after P-waves as they travel slower. This is because they have no rigidity to support sideways motion and therefore they cannot pass through liquids and gases – only solid material.  SURFACE WAVES unlike body waves travel only through the crust, surface waves are of a lower frequency than body waves, and are easily distinguished on a seismogram as a result. Though they arrive after body waves, it is surface waves that are almost entirely responsible for the damage and destruction associated with earthquakes. This damage and the strength of the surface waves are reduced in deeper earthquakes.
  6. 6. Andrija Mahorovicic Discontinuity  Mohorovičić discontinuity, often called Moho, is the boundary between Earth's crust and the mantle. It was discovered by Yugoslavian geophysicist Andrija Mohoroviči when analysing an earthquake in Croatia in 1909. Mohorovicic realised that the velocity of a seismic waves is related to the density of the material that it is moving through and that slower waves were travelling from the focus of the earthquake through the upper layer of the crust, whereas faster waves had accerlearated due to a higher density material being present at depth. He suggested that a change in density from 2.9g/cm3 to 3.3g/cm3 marks the boundary between the Earth’s crust.
  7. 7. Khan Academy video lecture on Andrija Mohorovicic
  8. 8. Shadow Zones  Later geologists found a shadow zone, an area between 105° and 142° from the source of the earthquake, within which they could not detect shock waves.  The explanation was that shock waves had passed from a solid to a liquid. Thus S-Waves would stop and P-Waves would be refracted. The geologists concluded that there was a change in density from 5.5g/cm3 at 2900km to a density of 10g/cm3. This was effectively the boundary between the mantle and the core. Within the earth there is an inner core of very dense solid material – the densit of the inner core goes up to as much as 13.6/cm3 at the centre of the Earth.  The nature of rock and sediment beneath the ground influences the patterns of shocks and vibrations during an earthquake. Unconsolidated sediments such as sand shake in a less predicable way than solid rock. Hence the damage is far greater to foundations of buildings. P waves from earthquakes can turn solid sediments into fluids like quicksand disrupting sub surface water conditions. This is known as liquefaction or fluidisation and can wreck foundations of large buildings and other structures.
  9. 9. The Richter and Mercalli Scales
  10. 10. Comparison of scales Richter Scale Mercalli Scale Measures: The energy released by the earthquake. The effects caused by the earthquake. Measuring Tool: Seismograph Observation Calculation: Base-10 logarithmic scale obtained by calculating logarithm of the amplitude of waves. Quantified from observation of effect on earth’s surface, human, objects and man-made structures Scale: From 2.0 to 10.0+ (never recorded). A 3.0 earthquake is 10 times stronger than a 2.0 earthquake and 100x stronger than a 1.0 quake. Scale of I-XII, I being not felt, XII being catastrophe. Consistency: Varies at different distances from the epicenter, but one value is given for the earthquake as a whole. Varies depending on distance from epicenter Problems: Doesn't’t take damage into account Speculative
  11. 11. Factors affecting earthquake damage  Strength and depth of earthquake + Number of aftershocks: the stronger the earthquake the more damage it can do. For example, an earthquake of 6.0 on the Richter scale is 100x more powerful than one of 4.0; the more aftershocks there are the greater the damage that Is done. Earthquakes that occur close to the surface (shallow-focus earthquakes) potentially should do more damage than deep focus earthquakes as more of the energy of the later is absorbed by overlying rocks.  Population density: if an earthquake that hits an area of high population density such as the Tokyo region of Japan, could inflict far more damage than one that hits an area of low population and building density.  Type of buildings: MEDCs generally have better quality buildings, more emergency services and funds to recover from disasters. People in MEDCs are more likely also not have insurance cover than those in LEDCs and are better educated as to how to respond in such events.  Time of day: An earthquake during a busy time, such as rush hour, may cause more deaths than one at a quiet time. Industrial and commercial areas have fewer people on them on Sundays, homes have more people in them at night.  Distance from the epicentre: The closer a place is to the epicentre of the earthquake the greater the damage that is done.  Type of rocks and sediments: loose materials may act like liquid when shaken, a process known as liquefaction; solid rock is much safer and buildings should be built on flat areas formed of solid rock.  Secondary hazards: an earthquake may cause mudslides and tsunamis and fires; also contaminated water, disease, hunger and hypothermia.  Economic development: this affects the level of preparedness and effectiveness of emergency response services, access to technology and quality of health services.
  12. 12. Resultant hazards of earthquakes  Most earthquakes occur with little if any advance warning. Some places, such as California and Tokyo which have considerable experience of earthquakes and have developed earthquake action plans and information programmes to increase public awareness about what to do in an earthquake.  Most problems are associated with damage to buildings, structures and transport systems. The collapse of building structures is the direct cause of many injuries and deaths, but it also reduces the effect of the emergency services. In some cases more damage in caused by the aftershocks that follow the main earthquake, as they shake the already weakened structures. Aftershocks are more subdued but long lasting and more frequent than the main tremor. Buildings partly damaged during the earthquake may be completely destroyed by the aftershocks.  Some earthquakes involve surface displacement, generally along fault lines. This may lead to the fracture of gas pipes, as well as causing damage to lines of communication. The cost of repairing such fractures is considerable.  Earthquakes may cause other geomorphological hazards such as landslides, liquefaction (the conversion of unconsolidated sediments into materials that act like liquids) and tsunamis.  There are both primary affects and secondary affects. Primary effects are the immediate damage caused by the quake such as collapsing of infrastructure, whereas secondary effects are after-affects of a earthquake such as tsunamis, landslides and spread of disease.
  13. 13. Earthquakes and human activities  Human activities can trigger earthquakes, or alter the magnitude and frequency of earthquakes in three main ways… 1. Through underground disposal of liquid wastes 2. By underground nuclear testing and explosions 3. By increasing crustal loading
  14. 14. Disposal of liquid waste  Water that is salty or polluted by chemicals needs to be disposed of in a manner that prevents it from contaminating freshwater sources. It is usually most economical to isolate and inject it into deep underground wells, below any aquifers that provide drinking water. This process is known as wastewater injection.  Most wastewater currently disposed of is saltwater found in the same rock formations as oil and gas. This saltwater comes up as a by-product during the oil and gas production process. It is often in large volumes and is too salty or contains minerals and other chemicals that economically preclude it from being cleaned and released at the surface or reused.  In Denver, Colorado, wastewater was injected into underlying rocks during the 1960s. Water was contaminated by chemical warfare agents, and the toxic wastes were too costly to transport off-site for disposal. Thus it was decided to dispose of it down a well over 3500m deep. Disposal began in March 1962 and was followed soon afterwards by a series of minor earthquakes, in an area previously free of earthquake activity. Between 1962-65 over 700 minor earthquakes are monitored in the region.  The injection of the liquid waste into the bedrock lubricated and reactivated a series of deep underground faults which had been inactive for a long time. The more wastewater was put down the well, the larger the number or minor earthquakes.
  15. 15. Underground Nuclear Testing  Underground nuclear testing has triggered earthquakes in a number of places. In 1968 testing of a series of 1200 tonne bombs in Nevada set off over 30 minor earthquakes in the area over the following three days. The explosion from nuclear testing results in a simultaneous release of plate tension which results in minor earthquakes.
  16. 16. Increased crustal loading  Earthquakes can be caused by adding increased loads on previously stable land surfaces. For example, the weight of water behind large reservoirs can trigger earthquakes.
  17. 17. What should people do about earthquakes  People deal with earthquakes in a number of ways. These include: 1. Do nothing and accept the hazard 2. Adjust to living in a hazardous environment – strengthen your home 3. Leave the Area.  The main ways for preparing for earthquakes include: 1. Better forecasting and warning 2. Improve building design/location 3. Establish emergency procedures There are a number of ways of predicting and monitoring earthquakes, which involve the measurement of… 1. Small-scale ground surface changes 2. Small-scale uplift or subsidence 3. Ground tilt 4. Changes in rock stress 5. Micro-earthquake activity (clusters of small quakes) 6. Anomalies in the Earth’s magnetic field 7. Changes in electrical resistivity of rocks.
  18. 18. Volcanoes A volcano is an opening in the Earth’s crust where magma – a mixture of red-hot liquid rock, mineral crystals, rock fragments and dissolved gases from inside the planet erupts onto the surface.
  19. 19. Types of Volcanoes  There are two main types of Volcanoes: 1. Shield, 2. Cone  The shape of a volcano depends on the type of lava it contains.  Very hot, runny lava produces gently sloping shield volcanoes (Hawaiian type)  Thick material produces cone-shaped volcanoes (Plinian type). These may be the result of many volcanic eruptions over a long period of time.  The shape of the volcano also depends on the amount of change there has been since the volcanic eruption.  Cone volcanoes are associated with destructive plate boundaries, whereas shield volcanoes are characteristic of constructive boundaries and hotspots.
  20. 20. Types of Volcanoes: Shield  Shield volcanoes are low with gently sloping sides and are formed from layers of lava.  Eruptions are typically non-explosive but frequent.  Shield volcanoes produce fast flowing fluid [lava] that can flow for many miles.  Shield volcanoes are usually found at constructive boundaries and sometimes at volcanic hotspots. Examples of the largest shield volcano is Mauna loa on Hawaii. It is also one of the Earth’s most active volcanoes and is carefully monitored. The most recent eruption was in 1984.
  21. 21. Types of volcanoes: Cone  Acid lava that flows from cone or dome volcanoes is much more viscous than lava which flows from shield volcanoes.  Dome volcanoes have much steeper sides than shield volcanoes. This is because the lava is thick and sticky. It cannot flow very far before it cools and hardens.  An example is Puy de Dome in the Auvergne region of France which last erupted over 1 million
  22. 22. Volcanoes are classified in a number of ways. These include the type of flow, type of eruption and level of activity….  Aa flow is a few metres thick. It consists of two distinct zones – an upper rubbly part, and a lower part of solid lava which cools slowly. Aa surfaces are a loose jumble or irregularly shaped cindery blocks with sharp sides.  By contrast, pahoehoe flow is the least viscous of all lavas; rates of advance can be slow. It has a cool surface, with flow underneath the surface. Pahoehoe surfaces can be smooth and glossy but may also have cavities; surfaces may also be crumpled with channels  The amount of silica makes the difference between volcanoes that erupt continuously, such as those on Iceland and Hawaii and those where eruptions are infrequent but violent, such as Japan and Philippines.  Lava is released where the oceans meet the continents absorbs silica-rich sediments; this causes the lava to become less viscous and block the vents until enough pressure has built up to break them open. Each year about 20km2 of land is covered by lava flows. These may initially reach temperatures of over 1000°c, resulting in severe social and economic disruption. However, cooled lava flows are very fertile and therefore attract dense population settlement and intense agriculture production.  There are a number of ways of reducing lava flows. These include spraying them with water, bombing them and seeding the lava with foreign nuclei.  Volcanoes are found in three states – extinct, dormant and active. An extinct volcano will never erupt again. A dormant volcano has not erupted in 2000 years. An active volcano has erupted recently and is likely to erupt again.
  23. 23. Types of volcanic eruptions  Volcanic eruptions are often thought of as cataclysmic explosions that produce vast quantities of lava, ash and other volcanic materials. However, volcanoes can actually erupt in a range of different ways. A volcano can erupt in a range of different ways during different eruptions and even during different stages in the same eruption.  These different types of volcanic eruptions include… 1. Plinian eruptions 2. Hawaiian eruptions. 3. Strombolian 4. Vulcanian 5. Vesuvian 6. Icelandic
  24. 24. Types of eruptions
  25. 25. Plinian Eruptions  These are the most explosive and violent of volcanic eruptions. They produce huge plumes of ash and gas that typically takes the shape of a huge mushroom cloud.  In Plinian Eruptions the magma has high silica content. They are highly explosive and the AD79 eruption that buried Pompeii and Herculaneum was one of these.  Plinian eruptions are started by highly viscous magma that has high gas content. As the magma emerges it depressurizes and this allows the gas to expand, propelling pyroclastic material as high as 45 km in the air, at hundreds of feet per second, up and out of the Troposphere. These eruptions can last for days and create a sustained and tall eruption plume, which drops huge amount of tephra, fallen volcanic material, on surrounding areas. Additionally, a Plinian eruption can produce extremely fast moving lava flows that destroy everything in their path.
  26. 26. Hawaiian Eruptions  In Hawaiian Eruptions the lava is more basic and basaltic, with low gas pressures and low silica content. This means the lava is very runny.  These eruptions are generally not explosive or destructive and do not throw huge amounts of Tephra or pyroclastic material in the air.  Instead they produce low-viscosity, low-gas- content lava that flows over large areas producing gently sloping shield volcanoes and lava plateaus.  Eruptions can form fire fountains, Lava thrust up to 50m in the air for many hours. The general eruption style is a steady lava flow from a central vent, which can produce wide lava lakes, ponds of lava forming in craters or other depressions.
  27. 27. Strombolian eruptions  Strombolian eruptions are named after Stromboli in Italy.  The effects are impressive but not particularly dangerous.  They eject short bursts of lava 15 to 90 meters in the air. The lava has a fairly high viscosity (it’s quite thick due to its high silica content), so gas pressure builds up before material can be ejected from the volcano.  These regular explosions can produce impressive booming sounds, however the eruptions are relatively small.  Lava flows from Strombolian eruptions are not common though they do throw out large quantities of pyroclastic rock.  Eruptions are commonly marked by a white cloud of steam emitted from the crater
  28. 28. Types of eruptions Icelandic lava eruptions  Characterised by persistent fissure eruption  Large quantities of basaltic lava build up vast horizontal plains Vulcanian eruptions  Violent gas explosions blast out plugs of sticky or cooled lava.  Fragments build up into cones of ash and pumice.  Vulcanian eruptions occur when there is very viscious lava which solidifies rapidly after an explosion  Often the eruption clears a blocked vent and spews large quantities of volcanic ash into the atmosphere. Vesuvian eruptions  Characterised by very powerful blasts of gas pushing ash clouds high into the sky  More violent than Vulcanian eruptions
  29. 29. Volcanic Hazards  Volcanic hazards can be divided into six main categories: 1. Lava flows 2. Ballistics and Tephra louds 3. Pyroclastic flows 4. Gases and acid rain 5. Lahars (mudflows) 6. Glacier bursts
  30. 30. Volcanic hazards  As and debris falls steadily from the volcanic cloud, blanketing the ground with a deposit known as a pyroclastic fall. These can be very dangerous, especially as the fine ash particles can damage people’s lungs. Also ash is fairly heavy – a small layer only a few centimetres thick can be enough to cause a building to collapse. Dust and fine particles also cause havoc with global climate patterns.  A pyroclastic flow is a fast-moving current of hot gas and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph). The gas can reach temperatures of about 1,000 °C. Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. They are a common and devastating result of certain explosive volcanic eruptions.  Lahars are another hazard associated with volcanoes. A combination of heavy rain and unstable ash increase the hazard of lahars. Lahars are extremely dangerous especially to those living in valley areas near a volcano. Lahars can undercut banks and cause houses on those banks to be destroyed. Lahars can bury and destroy manmade structures including roads and bridges. At Nevado del Ruiz, lahars destroyed an entire city; filling the first floor of a hospital with mud, breaking windows, floating cars, and leaving debris in the tops of trees  The hazards associated with volcanic eruption vary spatially. Close the volcano people are at risk of large fragments of debris, ash falls and poisonous gases. Whereas, further away pyroclastic flows may prove hazardous and mudflows and debris flows may have an impact on more distant settlements.
  31. 31. Volcanic Hazards Primary Hazards Secondary Hazards Socio-Economic impacts • Pyroclastic flows • Volcanic bombs • Lava flows • Ash fallout • Volcanic gases • Earthquakes • Atmospheric ash fallout • Landslides • Tsunamis • Acid rainfall • Lahars • Destruction of settlements • Loss of life • Loss of farmland and forests • Destruction of infrastructure – roads, airstrips and port facilities • Disruption of communications and transporrts.
  32. 32. Volcanic Strength  The strength of a volcano is measured by the Volcanic Explosive index (VEI). This is based on the amount of material ejected in the explosion, the height of the cloud it creates, and the amount of damage caused. Any explosion above level 5 is considered to be very large and violent. A VEI 8 refers to a super volcano.
  33. 33. Predicting volcanoes  Scientists are increasingly successful in predicting volcanoes. Since 1980 they have correctly predicted 19 of Mt St Helens, 22 eruptions and Alaska's redoubt volcano in 1989. There have been false alarms too: in 1976 72000 residents of Guadeloupe were forced in leave their homes, and in 1980 Mammoth Lake in California suffered from a reduction in tourist numbers owing to mounting concern regarding volcanic activity.  Volcanoes are easier to predict than earthquakes since there are certain signs. The main ways of predicting volcanoes include monitoring using… 1. Seismometers to record swarms of tiny earthquakes that occur as the magma rises 2. Chemical sensors to measure increased sulphur levels 3. Lasers to detect the physical swelling of the volcano 4. Ultrasound to monitor low-frequency waves in the magma, resulting from the surge of gas and molten rock 5. Observations  However, it is not always possible to state exactly when a volcanic eruption will happen.
  34. 34. Living with a volcano  People often choose to live in volcanic areas because they are useful in a variety of ways…  Some countries, such as Iceland and the Philippines, were created by volcanic activity.  Some volcanic soils are rich, deep and fertile and allow intensive agriculture, for example in Java. However, in other areas such as Sumatra and Iceland the soils are poor due to leaching or climate.  Some volcanoes are culturally symbolic and are apart of the national identity such as Mt Fuji in Japan.  People live close to volcanoes because Geothermal energy can be harnessed by using the steam from underground which has been heated by the Earth's magma. This steam is used to drive turbines in geothermal power stations to produce electricity for domestic and industrial use. Countries such as Iceland and New Zealand use this method of generating electricity.  Volcanoes attract millions of visitors around the world every year. Apart from the volcano itself, hot springs and geysers can also bring in the tourists. This creates many jobs for people in the tourism industry. This includes work in hotels, restaurants and gift shops. Often locals are also employed as tour guides.
  35. 35. Secondary hazards of tectonic events
  36. 36. Lahar  One hazard that is closely associated with volcanic activity is the lahar:  Rain brings soot and ash back to ground and this becomes a heavily saturated mudflow  Heat from volcanoes melts snow and ice – the resulting flow picks up sediment and turns it into a destructive lahar.  Example: Nevado del Ruiz, Colombia and Mt. Ruapehu New Zealand
  37. 37. Tsunami  The term tsunami is Japanese for ‘harbour wave’  90% of tsunamis occur in the Pacific basin.  They are generally caused by earthquakes but can be caused by volcanoes and landslides.  Tsunamis have the potential to cause widespread disaster, as was the case in the South Asian tsunami in 2004, and Japan tsunami in 2011. 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 alarm once a tsunami has started. In the cases of submarine volcanoes it is possible to monitor these to predict the risk of tsunami. The first effective tsunami warning system was developed in 1948 in the Pacific, following the 1946 tsunami. The system consisted of over 50 tidal stations and 31 seismographic stations, spread between Alaska, Hong Kong and Cape Horn. When water passes a critical threshold a warning is automatically sent to Honolulu. In addition, the earthquake epicentre is plotted and magnitude investigated. Its effectiveness has been improved by the use of satellites. In theory there is time to issue warnings. However, the impacts will vary with shoreline morphology. Many LEDCs lack early warning systems, and as a result tsunamis can have dire consequences in such
  38. 38. Factors affecting the perception of risk  At an individual level there are three important influences upon an individuals response to any hazardous event: 1. Experience: the more experience a person has of environmental hazards the greater the adjustment to the hazard. 2. Material well-being: those who are better off have more choices. 3. Personality: is the person a leader or a follower, a risk- taker or risk-minimiser?  Ultimately there are just three choices: 1. Do nothing and accept the hazard 2. Adjust to the situation of living in a hazardous environment 3. Leave the area. The level of adjustment will depend, in part, upon the risks caused by the hazard… 1. Identification of the hazards 2. Estimation of the risk 3. Evaluation of the cost caused by hazard.
  39. 39. Hazardous environments resulting from mass movements
  40. 40. What is mass movement?  Mass movement can be defined as the large scale movement of weathered material in response to gravity. Essentially, it’s when a cliff or other structure that is not horizontally orientated has been weathered to the point at which it starts to collapse.  Mass movements can occur in many ways…  As slow movements such as soil creep  As fast movements, such as avalanches  As dry movements, such as rock falls  As fluid movements such as mudflows.
  41. 41. Factors affecting mass movement  Slope of the land surface: When the slope gradient is steep, mass movement is rapid.  Water content: Water acts as a lubricant, which makes it easier for material to move. Following a period of heavy rain, regolith is heavier and flows more quickly.  Human activity: Hills are often cut into during the construction of roads. This makes the hill unstable, which can lead to mass movement. The vibrations from machinery and traffic can also result in mass movement, as can deforestation.  Tectonic activity: volcanic activity can lead to the movement of material downslope. Mudflows (lahars), occur when the snow or ice covering a crater melts during an eruption. This mater mixes with soil to form mud. Earthquakes can also cause areas of hills or mountains to move downslope.  Plants and trees: the tree/plant roots bind soil in place and prevent mass movement.  Slope material: Mass movement is also affected my slope material, whether it is consolidated (such as rocks) or unconsolidated.  Geological structure: Rocks with faults, and potential weaknesses within it are more vulnerable to weathering and less resistant to downslope movement.
  42. 42. Shear stress and resistance  The likelihood of a slope failing depends on the relative strength and resistance of the slope, compared with the force that is trying to move it.  Mass movements occur when the shear stress on a slope exceeds the shear resistance – therefore the slope can not overcome the forces of gravity and a mass movement begins.  Gravity has two effects, it can act to move the material downslope (slide component) or it can act to stick the particles to the slide (stick component).
  43. 43. Classification of mass movements  Mass movements are classified in a number of ways, including speed of movement and the amount of water present. In addition it is possible to distinguish between different types of movement, such as falls, flows, slides and slumps.  Slow movements: soil creep, solifluction  Fast movements: earth flow, mudflow  Rapid movements: slides, rock falls, slumps, avalanches Check out AS level notes for description of each mass movement type.
  44. 44. Avalanches  Avalanches are mass movements of snow and ice. Newly fallen snow may fall off older snow, especially in winter, while in spring martially thawed snow moves, often triggered by skiing.  Avalanches occur frequently on steep slopes over 22°, especially on north- facing slopes where the lack of sun inhibits the stabilisation of the snow.  They are also very fast. Average speeds in an avalanche are 40-60km per hour, but speeds of up to 200 per hour have been recorded in Japan.  Avalanches are classified in a number of ways…  The type of breakaway – from a point formed with loose snow, or from an area formed of a slab  Position of the sliding surface – the whole snow cover or just the surface  Water content – dry or wet avalanches  The form of the avalanche – whether it is channelled in cross section of open
  45. 45. Classification of avalanches
  46. 46. Avalanches  Although avalanches cannot be prevented, it is possible to reduce their impact through fences, rakes, wedges, afforestation etc. So why do avalanches occur?  The underlying processes in an avalanche are similar to those in a landslide. Snow gets its strength from the interlocking of snow crystals and cohesion caused by electrostatic bonding of snow crystals. The snow snow remains in place as long as its strength is greater than the stress exerted by its weight and the slope angle.  The process is complicated by the way in which snow crystals constantly change. Changes in overlying pressure, compaction by freshly fallen snow, temperature changes an the movement of melt water through the snow cause the crystal structure of the snow to change which may make it unstable causing an avalanche.  Loose avalanches, comprising fresh snow, usually occur soon after a snowfall. By contrast slab avalanches occur at a later date, when the snow has developed some cohesion. The latter are much bigger than loose avalanches and cause more destruction, often started by a sudden rise in temperature which causes melting. The melt water lubricates the slab and makes it unstable.  Many of the avalanches occur in spring when the snowpack is large and temperatures are rising.
  47. 47. Avalanche video
  48. 48. Hazards resulting from atmospheric disturbances
  49. 49. Tropical storms (cyclones)  Tropical storms bring intense rainfall and very high winds, which may in turn cause storm surges and coastal flooding, and other hazards such as flooding and mudslides.  Tropical storms are also characterised by enormous quantities of water. This is due to their origin over tropical seas. High-intensity rainfall, as well as large totals – up to 500 mm in 24 hours invariably cause flooding.  Their path is erratic, so it is not always possible to give more than 12 hours notice of their position. This is insufficient for proper evacuation measures.  Tropical storms develop as intense low pressure systems move over tropical oceans. Winds spiral rapidly around a calm central area known as the eye.  The diameter of the whole storm may be as much as 800km although the very strong winds that cause most of the damage are found in a narrower belt up to 300km. In a mature tropical storm pressure may fall to as low as 880mb, this and the strong contrast in pressure between the eye and outer part of the storm leads to strong winds.  Tropical storms move excess heat from low latitudes to higher latitudes. They normally develop in the west-war flowing air just north of the equator. They begin life as a small-scale tropical depression, a localised area of low pressure that causes warm air to rise. This causes thunderstorms which persist for at least 24 hours and may develop into tropical storms, which have greater wind speeds of up to 117km/hour. However, only 10% of these tropical disturbances ever become tropical wind speeds above 118km/h
  50. 50. Conditions needed for tropical storm formation  Sea temperatures must be over 27° to a depth of 60m as the warm water gives of large qualities of heat when it is condensed – the driving force behind the tropical storm.  The low pressure area has to be far enough away from the equator so that the Coriolis force creates rotation in the rising air mass – if it is too close to the equator there is insufficient rotation and the tropical storm will not develop  Conditions must be unstable – some tropical low pressure systems develop into tropical storms but scientists are unsure why some do and others do not.
  51. 51. How are tropical storms measured?  Tropical storms are the most violent, damaging and frequent hazard to affect the tropical regions. They are measured on the Saffir-Simpson Scale, which is a 1-5 rating based on the tropical storm’s intensity. It is used to give and estimate of the potential property damage and flooding expected along the coast from a tropical storm landfall.  Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slop of the continental shelf and the shape of the coastline in the landfall region. Tropical storms can also cause considerable loss of life.
  52. 52. Saffir-Simpson Scale
  53. 53. Factors affecting impact of tropical storms  Tropical storm paths are unpredictable, which makes effective management of the threat difficult.  The distribution of the population will depend whether the risk associated with tropical storm is increased or reduced. Places like the Caribbean islands, for e.g. where much of the population lives in coastal settlements and is exposed to increase sea levels and flooding therefore will experience far greater impacts then that of a sparsely populated in land area.  Hazard migration depends upon the effectiveness of the human response to natural events – including urban planning laws, emergency planning, evacuation measures and relief operations such as re-housing schemes and distribution of food aid and clean water.  LEDCs continue to lose more lives to natural hazards, due to inadequate planning and preparation.
  54. 54. Formation clip
  55. 55. Tropical storm management  Information regarding tropical storms is received from a number of sources including… 1. Satellite images 2. Aircraft that fly into the eye of the tropical storm to record weather information 3. Weather stations at ground levels 4. Radars that monitor areas of intense rainfall.
  56. 56. Preparing for tropical storms Beforethestorm Know where your emergency shelters are Have disaster supplies on hand Protect your windows Trim back branches from trees Check home and car insurance Make arrangements for pets and livestock Duringthestorm Listen to the radio or tv for storm progress Check emergency supplies Make sure your car is full of fuel Bring in outdoor objects and anchor objects that cannot be brought inside Secure buildings by closing and boarding up windows Remove outside antennas and satellite dishes Afterthestorm Assist in search and rescue Seek medical attention for persons injured Clean up debris and effect temporary repairs Report damage to utilities Watch out for secondary hazards
  57. 57. Reducing vulnerability of structures and infrastructures  New buildings should be designed to be wind and water resistant. Design standards are usually incorporated into building codes  Communication and utility lines should be located away from the coastal area or installed underground.  Areas of building should be improved by raising the ground level to protect against flood and storm surges  Protective river embankments, levees and coastal dikes should be regularly inspected for breaches due to erosion and opportunities should be taken to plant mangrove trees to reduce breaking wave energy.
  58. 58. Tornadoes  Tornadoes are small and short-lived but highly destructive storms. Because of their severe nature and small size, comparatively little is known about them. Measurement and observation within them are difficult.  A few low-lying, armoured probes called ‘turtles’ have been placed successfully in tornadoes.  Tornadoes consist of elongated funnels of cloud which descend from the base of a well-developed cumulonimbus cloud, eventually making contact with the ground beneath.  In order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base.  Within tornadoes are rotating violent winds, perhaps exceeding 100m/s  Pressure gradients in a tornado can reach an estimated 25 mb per 100m.
  59. 59. How tornadoes form  Moisture, instability, lift and wind shear are the four key ingredients in tornado formation.  Most tornadoes rotate cyclonically (anticlockwise in the northern hemisphere and clockwise in the southern hemisphere)  The standard explanation is that warm moist air meets cold dry air to form a tornado  Many thunderstorms form under these conditions, which never even come close to producing tornadoes. Even when the large-scale environment is extremely favourable for tornado-type thunderstorms, not every thunderstorm spawns a tornado.  The most destructive and deadly tornadoes develop from super cells (which are rotation thunderstorms with a well-defined low pressure system called a mesocyclone)  Tornadoes can last from several seconds to more than an hour.
  60. 60. Step by step formation  Step 1: Like all winds and storms, tornadoes begin when the sun heats up the surface of the land. As the warm, less heavy air begins to rise, it meets the colder, heavier air above it. Note that wind shears make it even easier to set them off. A wind shear is when two winds at different levels and speeds above the ground blow together in a location. Step 2: The faster moving air begins to spin and roll over the slower wind. As it rolls on, it gathers pace and grow in size. Step 3: At this stage, it is an invisible, horizontal wind spinning and rolling like a cylinder. As the winds continue to build up, stronger and more powerful warm air forces the spinning winds vertically upward, causing an updraft. Step 4: With more warm air rising, the spinning air encounters more updraft. The winds spin faster, vertically upwards, and gains more momentum.  Step 5: At this stage, the spinning winds, creates a vortex and the wind has enough energy to fuel itself. Step 6: The tornado is fully formed now and moving in the direction of the thunderstorm winds. When the pointed part of the tornado touched the ground from the cloud, it is often referred to as 'touch down' As it moves it rips off things along its patch.
  61. 61. Ted Talk: How tornadoes form Press image – a play button will show. Click this to watch…
  62. 62. Tornado damage  About a thousand tornadoes hit the USA each year with an average of 60 people dying per year from them. A tornado’s impact as a hazard is extreme with three damaging factors at work… 1. Winds are often so strong that objects in the tornado’s path are simply removed or very severely damaged 2. Strong rotational movement tends to twist objects from their fixings, and strong uplift can carry some debris upwards into the cloud. 3. The very low atmospheric pressure near the vortex centre is a major source of damage. When a tornado approaches a building, external pressure is rapidly reduced, and unless there is a nearly simultaneous and equivalent decrease in internal pressure, the walls and roof may explode outwards in the process of equalising the pressure differences.  Most tornado damage is due to multiple-vortex tornadoes or very small, intense single-vortex tornadoes. The wind in most multiple-vortex tornadoes may only be strong enough to do minor damage to a particular house. But one of the smaller sub vortexes, may strike the house next door with winds over 300m/hr causing complete destruction. Also there are great differences, in construction from one building to the next so whilst one building may be flattened the other may be barely touched.  Although winds in the strongest tornadoes may far exceed those in the strongest tropical storms, tropical storms typically cause much more damage. Economically tornadoes cause about 1/10 as much damage per year, on average, as tropical storms.  Tropical storms tend to cause much more overall destruction due to their much larger size, longer duration and variety of ways they damage property. Whilst tropical storms tend to be tens or hundreds of km across lasting many hours, tornadoes tend to be a few hundred yards in diameter and last only for a matter of minutes.
  63. 63. Tornado Fujita damage scale
  64. 64. Managing tornadoes  The main problem with anything that could realistically stand a chance of affecting a tornado (for e.g. an atomic bomb) is that it would be even more deadly and destructive than the tornado itself.  Lesser things like huge piles of dry ice would be too hard to deploy in the right place fast enough, and would probably not have a significant effect on the tornado  Nor is there any proof that seeding can or cannot change tornado potential in a thunderstorm. This is because there is no way of knowing that the things a thunderstorm does after it has been seeded would not have happened anyway.  This includes any presence or lack of rain, hail, wind gusts or tornadoes. Because the effects of seeding are impossible to prove or disprove, there is a great deal of controversy among meteorologists about whether it works, and if so, under what conditions and to what extent.
  65. 65. Sustainable management of hazardous environments
  66. 66. Assessing and mitigating damaging effects of mass movements  Landslides and other forms of mass movement are widespread and cause extensive damage and loss of life each year. With careful analysis and planning, together with appropriate stabilisation techniques, the impacts of mass movements can be reduced or eliminated.  Assessment of the hazards posed by potential mass movement events are based partly on past events, to evaluate their magnitude and frequency. In addition mapping and testing of soil and rock properties determines their susceptibility to destabilising processes. Maps showing areas that could be affected by mass movement processes are important tools for land use planners.  Eliminating or restricting human activities in areas where slides are likely may be the best way to reduce damage and loss of life. Land that is susceptible to mild failures may be suitable for some forms of development (recreation or parkland) but not others (such as residential or industrial).  Early warning systems can provide forecasts of intense rain. High-risk areas can be monitored and remedial action taken.  In addition to assessment, prediction and early warning, some engineering schemes can be applied to reduce the damage of mass wasting. These include retaining devices, drainage pipes, grading of slope and diversion walls.  Concrete blocks or gabions may be used to strengthen slopes. Slopes subject to creep can be stabilised by draining or pumping water from saturated sediment.  Over steepened slopes can be made gentler by regrading. However, not all communities can afford such measures and so may opt for low-cost sustainable forms of management.
  67. 67. Hazard management, risk assessment and perception  Hazard management includes a body of theory which includes: risk, prediction, prevention, event and recovery.
  68. 68. Learning to live with Earthquakes  Most places with a history of earthquakes have developed plans that enable people to deal with them. The aim is to reduce the effect of the earthquakes and thus save lives, buildings and money.  The ways of reducing earthquake impact include…  earthquake prediction,  building design,  flood prevention  and public information.
  69. 69. 1. Preparation  Earthquakes killed about 1.5 million people in the 20th century and the number of earthquakes appears to be rising. Most of the deaths were caused by the collapse of unsuitable and poorly designed buildings. More than a third of the world’s largest and fastest growing cities are located in regions of high earthquake risks, so the problems are likely to intensify.  It is difficult to stop an earthquake from happening, so prevention normally involves minimising the prospect of death, injury or damage by controlling building in high-risk areas and using aseismic designs. In addition warning systems can be used to warn people of an imminent earthquake and inform them of what to do when it does happen.  Insurance schemes are another form of preparation by sharing the costs between a wide group of people.  The seismic gap theory states that that over a prolonged period of time all parts of a plate boundary must move by almost the same amount. Thus if one part of the plate boundary has not moved and others have, then the part that has not moved is likely to move next. This theory has been used successfully to suggest that an earthquake was likely in the Loma Preita segment of the San Andreas fault.
  70. 70. 2. Building design  Increasingly, as the availability of building land is reduced, more and more people are living in seismic areas. This increases the potential impact of an earthquake. However, buildings can be designed to withstand the ground-shaking that occurs in an earthquake..  Single story buildings are more suitable than multi-storey structures, because this reduces the number of people at risk, and the threat of collapse over roads and vacation routes.  Some tall buildings are built with a soft storey at the bottom, such as a car park raised on pillars. This collapses in an earthquake, so that the upper floors sink down onto it and this cushions the impact.  Mounting the foundations of a building on rubber mounts which allow the ground to move under the building is widely used. This isolates the building from the tremors.  Building reinforcement strategies include building on foundations built deep into underlying bedrock, and the use of steel-constructed frames that can withstand shaking  Land use planning is another important way to reducing earthquake risk.
  71. 71. Controlling earthquakes  In theory, by altering the fluid pressure deep underground at the point of greatest stress in the fault line, a series of small and less damaging earthquake events may be triggered which could release the energy that would otherwise build up and create a major event.  Additionally, a series of controlled underground nuclear explosions might relieve stress before it reaches critical levels.

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