Hazardous Earth Flashcards
1
Q
What does the Earths interior structure consist of?
A
Crust-
*Continental + Oceanic
Mantle -
*Lithosphere (Includes crust to 100km) - rigid
*Asthenosphere (100km- 300km) - Rheid
*Mesosphere (300km - 2900km) - Solid because pressure is too high
Core-
Outer core -
Liquid
Inner core -
solid due to pressure
Undergoes radioactive decay that provides heat the the mantle to drive convection currents
2
Q
What are the 3 main processes that are believed to move plates?
A
Convection Currents/Mantle Drag
Slab Pull
Ridge Push
3
Q
What is the thickness, density and composition of continental and oceanic crust?
A
Continental
35KM Thick
2.7 g/cm^3
Granitic, Silicon, and aluminium
Oceanic
7KM Thick
2.9 g/cm^3
Basaltic, silicon and magnesium
4
Q
Explain mantle drag/convection currents
A
Are found in the asthenosphere, caused by the rising heat from radioactive decay of isotopes deep in the core. As a result, the rheid layer in the asthenosphere flows carrying the solid lithosphere on top of it.
There are two types/theories of convection currents: Shallow and deep convection currents.
The shallow convection current theory suggests there are two sets of convection currents, one in the asthenosphere and one above, that move together to move the plates.
The deep convection current theory suggests the mantle circulates through all the layers.
5
Q
Explain ridge push
A
Magma rises as the plates move apart. The magma cools to form new plate material. As it cools It becomes denser and slides down away from the ridge. This causes other plates to move away from each other.
6
Q
Explain slab pull
A
Is another gravitational force generated by plates subducting. Develops because the lithosphere is denser than the underlying asthenosphere and sinks like a stone in the water, pulling the plate behind it.
7
Q
Is there a dominant process that moves plates?
A
No, it is the interaction between all three theories that work together to move the plates, however, it is more ridge push and slab pull than convection currents.
8
Q
What are the 4 interrelated ideas of continental drift?
A
1- Wegner’s Theories (Geological and Biological)
2- Palaeomagnetism
3- Sea Floor Spreading
4- Age of sea floor rocks
9
Q
What are the 6 pieces of evidence that Wegener used to prove continental drift?
A
RIFFJM
Rocks aka geological fit
Ice aka glacial fit
Fold Mountains aka tectonic fit
Fossil record aka fossil fit
Jigsaw fit
10
Q
Explain the jigsaw fit (Alfred Wegener’s theories)
A
Africa and South America both fit together at a depth of 1000 meters. However, they dont fit perfectly because of gaps however these can be explained by:
-Erosion of the coastlines would have been different 237 Ma
-Deposition again would be different
- Rise in sea level since 237 Ma
-Isostatic change since 237 Ma
11
Q
Explain the geological fit (Alfred Wegener’s theories)
A
The geology of South America and Africa match up such as old fold mountains and cratons. Are around 200 Ma, and when the continents are joined together have the same age and rock type.
12
Q
Explain the tectonic fit (Alfred Wegener’s theories)
A
Fragments of a old fold mountain belt between 450-400 Ma found across Norway, Greenland, Scotland, Canada, Ireland and some other countries where these land masses where aligned.
13
Q
Explain the glacial fit (Alfred Wegener’s theories)
A
Evidence from 290 Ma of the effects of contemporaneous glaciation in South America, Australia, southern Africa, India and Antarctica. This suggests that these land masses were joined at this time, located close to the south pole (Gondwanaland). We can also see striations in the rocks that suggest glaciers were moving as they are basically scratch marks in the rock where the glacier was moving.
14
Q
Explain the fossil fit (Alfred Wegener’s theories)
A
Fossils of the same species were found across different continents. One is the Mesosaurus, found in South America and Africa. These species cannot swim across oceans and could not have evolved the same across different continents so the continents must have been joined. This is further proved my plant fossils found in Antarctica and Australia which cannot transfer across the sea to breed so these continents must have been joined.
15
Q
What is palaeomagnetism?
A
Is the study of the Earth’s ancient magnetic field. In the 1950s, technology designed to track submarines measured very small variations in the Earth’s magnetic field. When used by geologists the magnetic field showed up as a striped pattern across the ocean floor.
16
Q
How do the symmetrical magnetic orientation strips form on the sea floor?
A
1- At the MORs lava is extruded from the ridge creating basaltic igneous rocks forming new oceanic crust.
2- Iron is found in this lava flow, which is magnetic
3- When the lava cools at the MOR, iron particles are cooled and locked in the magnetic orientation pointing true north at the time it cooled
4- However, the Earths polarity is not constant and changes every 400k-500k years in reverses.
5- This explains the striped pattern across the ocean floor as each band shows a reversal.
6- When the palaeomagnetic data was observed from the studies of the mid Atlantic ridge in the 1960s it led to the idea of sea floor spreading
17
Q
How is palaeomagnetism used to prove continental drift?
A
The symmetrical pattern of the bands either side of the MOR indicated
Fresh molten rock from the asthenosphere reached the ocean floor at the MOR
The older rock had been pushed away from the MOR
The alternating pattern shows many polar reversals which happen every 300,000 years, which shows that the sea floor must have moved in order for older rocks to have alternating patterns on them
18
Q
How can we use the age of sea floor rocks to prove continental drift?
A
The youngest material is at the ridge and the oldest material is furthest away at the subduction zone at oceanic trenches where it returns to the asthenosphere to become molten again. This shows that the plates must have moved if older rocks are found at the subduction zones.
19
Q
What are the 3 types of plate boundaries?
A
Divergent
Convergent
Conservative
20
Q
What happens at MORs (Divergent plate boundary underwater)?
A
- Magma that rises up from the asthenosphere has the force to push apart plates via mantle drag, slab pull and ridge push
- Such splits in the crust tend to create MORs. These are submarine chain mountains that can get up to 3km high and 60km in length
- As the magma rises the ridged lithosphere and crustal rocks are forced up into a dome, this is because it is rigid, the stress created as the dome rises results in rocks fracturing
- This results in earthquakes, however if magma reaches the surface
21
Q
What are the main features of divergent plate boundaries?
A
Basalt Pillow Lavas
Black Smokers
Transform Faults
Rift Valleys
Submarine Mountains
22
Q
What are the three spreading speeds and what types of landforms do they create at Divergent Plate boundaries?
A
Fast Spreading (Up to 16.5 cm/yr) - Creates broad and smooth mountain chains, with no central rift valley
Medium Spreading (5-10cm/yr) - Poorly defined central rift valley, relatively smooth mountain chains
Slow Spreading(2-3cm/yr) - Steep sloped mountain chains, clearly defined rift valley
23
Q
Explain the formation of pillow lavas
A
Magma erupts directly onto the seabed and is cooled rapidly, which forms the rounded pillow lavas.
24
Q
Explain the formation of black smokers
A
At mid-ocean ridges, sea water seeps into faults and is super-heated. As it rises back to the surface, it causes changes in the basaltic rocks. Superheated jets of mineral-rich water re-emerge on the ocean floor, containing metal sulfates. Where they emerge, they are called “Hydrothermal vents.”
25
What is the case study used for a mid-ocean ridge that runs through a country?
The Mid-Atlantic Ridge, which runs through Iceland,
This is where the North American and Eurasian plates are moving away from each other. It is approximately 15,000km long and rises between 2-3km above the ocean floor and has a rift valley at its crest marking the location at which the two plates move apart.
26
How do rift valleys form?
1. The uprising magma from the asthenosphere creates a dominating effect. This creates tension in the brittle crust as it is stretched, which causes faulting.
2. As the faulting continues around the dome, it forms a sunken valley as the central collumn, known as the Graben, collapses, caused by gravitational foci parallel to the lines of faults. This movement causes many low-energy earthquakes to occur here. As the rift valley widens, magma rises, creating fissure eruptions along the fault lines.
3. Eventually, the rifty valley will sink below sea level, inundated with water. This is how the red sea between the African and Arabic penisula formed.
4. As the plate continues to move, it will create a new ocean.
27
What is the case study for a rift valley?
The Great Rift Valley in Africa
It stretches for 5000km from Israel to Mozambique. At the northern end of the system, the Arabian plate is moving north-eastward, while the African plate is moving south-westward. In some places, the valley has sunk below sea level, which has formed the red sea and further the dead sea.
28
What are the three types of convergent plate boundaries?
Oceanic-Oceanic
Oceanic-Continental
Continental-Continental
29
What happens at an oceanic-oceanic convergent plate boundary?
When two oceanic plates meet, the slightly denser one will be subducted, forming an oceanic trench. As the descending plate melts, magma rises to the surface, erupting as a chain of volcanoes known as an island arc.
30
What are some case studies for an oceanic-oceanic convergent plate boundary?
The Aleutian Islands and the Marian Trench
Indonesian Archipelago (Merapi, Anak Krakatau and Krakatau)
31
What happens at an oceanic-continental convergent plate boundary?
When a denser oceanic plate meets a less dense continental plate, the oceanic plate is forced down under the continental plate in a process called subduction. An oceanic trench forms where the subduction takes place. Also, as subduction occurs some of the sediment rocks and oceanic crust are scraped off onto the continental plate in a process called obduction. This forms accretionary wedges where the layers are deformed and metamorphosed.
32
What is the case study for the oceanic-continental convergent plate boundary?
The Andes. Here, the oceanic Nazca plate is moving eastwards towards the continental South American plate at about 7.9mm per year.
The oceanic trench formed here is called the Peru-Chile (Atacama Trench). The Andes are formed by the process of obduction.
33
How else do fold mountains such as the Andes form along oceanic-continental convergent plate boundaries?
As the oceanic crust subducts under the continental, it will still be saturated with sea water. When the crust starts to melt, flux melting occurs, making the magma more dense and rising upwards towards the surface. This causes vertical uplift of the crust and creates fold mountains.
34
What happens at a continental-continental convergent plate boundary (collision zone)?
When two continental plates with equal densities collide, due to their buoyancy, neither subducts, so it thickens the crust due to folding and faulting and pushes the crust vertically due to compressional forces. This faulting can create occasional shallow earthquakes.
35
What is the case study for a continental-continental convergent plate boundary (collision zone)?
The Himalayas. Extend for 2900jm reaching a max elevation of 8848 meters. This was formed when the Indian plate collided with the Eurasian plate, which scraped the seabed upwards which is why the mountains are made of sea sediments.
36
What are 5 factors that influence the type of volcanic activity at a location.
1. Type of plate boundary
2. Chemistry of lava
3. Viscosity of lava
4. Type of material erupted
5. How the eruptions take place
37
What is viscosity?
An indication of how well a substance flows.
38
What are the two categories that eruptions can be place into?
Explosive
Effusive
39
What are the 6 types of eruptions?
Icelandic
Hawaiian
Strombolian
Vesuvian
Vulcanian
Plinian
40
What are the two effusive eruptions?
Icelandic
Hawaiian
41
What products do effusive eruptions create?
Lava plateaus
Shield Volcano
42
What is the VEI of effusive eruptions?
0-1
43
What are the 4 explosive eruptions?
Strombolian
Vesuvian
Vulcanian
Plinian
44
What products do explosive eruptions create?
Calderas
Strato-volcanos
45
What is the VEI of explosive eruptions?
Strombolian - VEI = 2
Vulcanian - VEI = 3-4
Vesuvian - VEI = 4-5
Plinian - VEI = 5-8
46
Where are effusive volcanoes found?
Divergent plate boundaries (Iceland and Hawaii)
47
What type of lava do effusive volcanoes erupt?
Basic (basaltic) lava with a low silica percentage, low viscosity, and high temperature vesicles form
48
What is the style of eruption of effusive volcanoes?
Gas bubbles expand freely so explosion is limited
49
What materials are erupted from effusive volcanoes?
Gas and lava flows
50
What is the frequency of effusive volcanoes?
Frequently (Daily)
51
What is the shape of effusive volcanoes?
Shield volcano and lava plateau from multiple fissures
52
Where are explosive volcanoes found?
Convergent plate boundary
53
What type of lava do explosive volcanoes erupt?
Rhyolite and Andesitic (Silicic magma)
Acidic Magma
High silica percentage
Low temperature
High viscosity
54
What is the style of explosion of effusive volcanoes?
A violent burst of gas, highly explosive, at the top of the cone can be shattered and blown off, forming calderas.
55
What materials are erupted from explosive volcanoes?
Gas, dust, ash, lava flows, bombs, tephra, and pyroclastic flow
56
What is the frequency of explosive volcanoes?
Tend to have periods of no activity (Dormant)
57
What is the shape of explosive volcanoes?
Steep sides stratovolcanoes and calderas
58
What are lava plateaus?
Created at divergent plate boundaries where basic lava is free-flowing. These erupt from multiple fissures in the ground and can produce vast quantities over a period of hundreds of years to form basalt floods. They usually have a shape of 1 degree, so they are really flat.
59
What are flood basalts?
A very large area of basalt lava erupted over 100 - 1000 of yeas from multiple of eruption events.
60
What are some examples of lava plateaus?
Deccan Plateau in India: 500,000 km^2
Colombian Plateau in USA: 130,000 km^2
61
What are shield volcanoes?
Shield volcanoes are found at divergent plate boundaries, usually underwater along mid-ocean ridges.
Iceland is the exception, and it owes its creation to exceptionally high volcanic activity. These volcanoes have gentle, sloping sides but can build up after successive flows accumulate for long enough.
62
What are hot spots?
Is an area on Earth that exists over a mantle plume.
63
What is a mantle plume?
an area under the crust where magma is hotter than the surrounding magma. Heat from this extra-hot magma causes melting and thinning of the crust, which leads to widespread volcanic activity on the earth's surface above the mantle plume. Can cause both effusive and explosive eruptions.
64
What can hot spots create?
Chain islands: as the plates move over the hot spot, volcanoes will form. When the plates move again, this volcano will be moved off of the hot spot, causing the volcano to become extinct.
65
How many hot spots are there around the world?
40-50
66
What is the equation to calculate the rate of movement of a plate?
Distance on map/scale length x 100
67
What can chain islands tell us about plates?
How fast the plate is moving per year.
68
Where are most stratovolcanoes located?
Ring of fire
69
Describe a stratovolcano
Occur at convergent plate boundaries. They are made of layers of ash and acidic viscous andesitic or rhyolitic lava. They have a concave symmetrical pattern.
70
What are 11 features of a stratovolcano?
Magma chamber
Vents
Sills
Dykes
Layers of ash and lava
Flanks
Throat
Pyroclastic cone
Lava flows
Craters
Ash clouds
71
What are sills?
Where lava intrudes between layers, faults parallel to the layers
72
What are dykes?
Where lava intrudes at right angles to the layers through faults.
73
What makes a stratovolcano explosive?
Acidic magma such as rhyolite and andesite does not flow readily (it is viscous), so the vent of the stratovolcano can often be filled with a mass of solidified magma. This allows great pressure to build up. When fresh magma rises, violent eruptions can occur, blowing the top of the volcano off. This can sometimes lead to a caldera forming.
74
What are calderas?
Are volcanic creaters, which can be from 2-100 km in diameter. They develop when an explosive eruption destroys much of the cone and the underlying magma chamber is emptied, so the top collapses.
75
What is an example of a caldera?
Krakatoa is a volcano on Rakata Island in the Sunda Strait between Java and Sumatra in Indonesia. Its exploding eruption in 1883 was one of the most catastrophic in history. It formed a caldera 7 km wide. 32,000 people died, and tsunamis and global weather patterns were disrupted.
76
What are super-volcanoes?
Is used to describe volcanoes that have had eruptions of a magnitude of 8 on the VEI. This means that at one point it erupted more than 1000km^2 of material.
77
What are three examples of super-volcanoes?
Taupo, New Zealand
Toba, Sumatra, Indonesia
Long Valley, USA
78
What are two ways of knowing the impact of super-volcanoes if they erupt rarely?
Geological Evidence: How far the ash spread and its depth
Paleo-biological assessments: showing the effects the volcano had on ecosystems, such as mass mortalities.
79
What is the case study used for super-volcanoes?
Yellowstone
It is over a hot spot, and events date back to 2.1 MA, when a super-volcano created the huge 75 km^2 caldera.
Since then 2 more eruptions have occured...
Huckleberry Ridge
Lava Creek Turf
80
What are five misconceptions about super-volcanoes?
1. Yellowstone is overdue a high-magnitude eruption (Tectonic events do not follow a regular pattern)
2. When Yellowstone erupts, it will have severe global impacts (The most probable eruptions will be lava flow or hydrothermal events)
3. The Yellowstone magma chamber is growing (No evidence exists for growth in near-surface chamber of the size required for a super-volcanic eruption)
4. Earthquake data indicate magma moving Recent earthquakes are linked to fractures in brittle rocks. Not always associated with eruptions.
5. The caldera surface is rising (measurements have indicated both rises and falls in ground surfaces within the caldera). Can have rapid movement with no eruption.
81
What is measured to assess volcanic activity?
Magnitude and intensity
82
What is the VEI scale?
Logarithmic scale (x10) from 0 to 8 that takes in the following factors:
Volume of erupted material
The height at which the material reaches
Length of the eruption in hours
It is not useful for effusive eruptions.
83
What are volcanic hazards?
Refers to any potentially dangerous volcanic event that puts human livelihoods at risk.
84
What are some examples of local volcanic hazards?
Lava flows
Pyroclastic flows
Lahars
Jökulhlaups
Landslides
85
What are some examples of regional or global volcanic hazards?
Tephra
Ash clouds
Release of gas
Tsunamis
86
Describe tephra and ash (Volcanic hazard)
Tephra describes any material ejected from a volcano into the air. Volcanic products typically named according to clast size, which can range from meters down to microns in size
"Ash" refers to particles less than 2mm in size. Volcanic bombs describe particles greater than 6cm in size.
87
What is the case study used for ash and tephra that had local and global impacts?
Eyjafjallajökull, Iceland, 2010
88
What type of volcano is Eyjafjallajökull?
Strato-Volcano, 1km high, 3 km crater
89
How big was the eruption at Eyjafjallajökull?
VEI 4. Usually, there are 1 or 2, but in this case, a combination of weather and wind blowing towards Europe, ash, and a persistent eruption lasting 34 days magnified the impact. It was runny magma but then turned explosive. This was because the mixing of water and magma created massive amounts of steam and made it explosive, launching Tephra out.
90
What were the primary impacts of the Eyjafjallajökull eruption?
-Ash blocked out the sun
-Homes and roads damaged
-Services disrupted
-Crops destroyed by ash
-Cost billions of Euros in flight cancellations
-$130m per day loss
-The price of shares dropped by 2.5–3.3%
-Imports and exports of the country were affected
91
What opportunities did the eruption of Eyjafjallajökull bring?
Grounding of flights reduced emissions (2,8 million tons of CO2)
Other transportation companies, such as Eurostar
-Ash dissolved in North Atlantic, causing plankton to boom
-Campaign to increase tourism to depict the beauty of the country after the eruption.
92
What were the secondary effects of the Eyjafjallajökull eruption?
-Sports events were cancelled
-Fresh food imports stopped
-Industries affected by a lack of imported materials.
-Local water supplies were contaminated with fluoride.
-Flooding caused by glacial melt
93
What were the global impacts of the Eyjafjallajökull eruption?
Kenyan flowers and vegetables are rotting at Aiprots due to flights being cancelled, resulting in a loss of $3.1 million a day.
Normally, it exports 500 metric tons of flowers daily, with 97% being delivered to Europe.
94
What was done to reduce the impacts of the eruption of Eyjafjallajökull?
Brief evacuation of around 500 local people
Cancelled flights.
95
Summarise how volcanic gases are a hazard
Various gases can be released from a volcano before, during or after an eruption
They can cause harm locally, but they also have potential to affect the climate globally
When people are exposed to harmful volcanic gases by breathing them in or through contact with the skin and eyes. The health effects range from mild to serious, with occasional deadly exposures. After exposure, people may report difficulty breathing and itchy skin.
96
What are the 5 main gases that pose a threat to health?
Carbon Dioxide
Hydrogen Chloride
Hydrogen Fluoride
Hydrogen Sulphide
Sulphur Dioxide
97
What is the case study for local impacts of volcanic gases.
Lake Nyos in Cameroon 1986
98
What happened at Lake Nyos (LOCAL IMPACTS OF VOLCANIC GASES)
1700 people and 3000 cattle were killed by 1 billion m^3 of CO2 that was released from a volcano due to turbidity currents and wind on the water that covered the volcano.
99
What are the global impacts of volcanic gases?
Gases can create acid rain and change climates. High concentrations of volcanic gas could create acid rain, which could then damage crops and ecosystems far from the volcano. This is because sulfur dioxide can be oxidized by tropospheric ozone, dissolve in water, and create sulfuric acid.
If S02 reaches the atmosphere, it acts as an aerosol and reflects solar radiation (Albedo effect)
100
Summarise how lava flows are a hazard
Lava flows are flows of magma extruding onto the surface of a volcano. In general, it is very slow to cause a direct loss of life because it flows slowly, allowing sufficient time for people to be evacuated
It does, however, pose a hazard to infrastructure, agriculture, and properties as it can destroy everything in its path.
The viscosity of the lava flow, which affects the hazard
Low-viscosity lava, such as basaltic lava, is typically 1100–1200 degrees Celsius and flows over very long distances (several kilometres), so it may have more devastating impacts compared to high-viscosity lava, such as andesitic or rhyolitic lava, which is around 700–900 degrees Celsius and travels as slowly.
101
On what scale are lava flows a hazard?
Only local as they cannot travel far
102
Summarise how pyroclastic flows are a hazard
Pyroclastic flows are hot currents of rock debris, gas, dust, and ash that travel under the force of gravity as they tend to flow down hillsides, along valleys, and towards lower ground following the relief of the land.
They are extremely powerful and are hot (100–600 degrees C) They typically travel 110 km/h.
They can be caused either by a fountain collapse (an ash column) or a dome collapse.
Such as in Pompeii, 79 AD, caused instant death to those inside, destroyed buildings, and killed livestock.
103
On what scale are pyroclastic flows a hazard?
They are mostly local, as they tend to flow from the volcano and then slowly disperse when they lose energy on flatter ground.
104
Summarise how Lahars are a hazard
Lahars are volcanic mudfows made of volcanic debris and hot or cold water. They move at a range of 10–50 km/h. They can occur as a result of eruptions involving ice or snow, creating meltwater, or by heavy rainfall on a volcano. Lahars can occur at any time during an eruption (before, during, or after).
105
What is the case study used for Lahars?
Nevado Del Ruiz (The volcano) and Armero (Local town)
106
What happened at the Nevado del Ruiz and Armero in relation to lahars?
In 1985, 23,000 people died as a result of a lahar on the Nevado del Ruiz volcano in Nevado del Ruiz, the deadliest lahar recorded in history. This larhar traveled 30km to Armero, where it wiped out the town as well as the surrounding villages. This is an example of the local and regional impacts of the hazard, as it can affect more than one place that is near river channels.
107
Summarise how Jokulhlaups are a hazard
Jokulhlaups is an icelandic word that is used to describe a glacial outburst, a sudden release of water from a lake that lies under or close to a glacier. One of the triggers could be an eruption of a volcano that melts beneath the glacier and melts the overlying ice or weakens the dam made of moraine sediments.
This happened at the Grimstvotn volcano that sits above a glacier, causing floods on local towns
108
On what scale are pyroclastic flows a hazard?
It can be both local and regional, depending on the amount of water released, proximity to river channels, etc.
109
Summarise how tsunamis are a hazard
This hazard is caused by earthquakes and sometimes volcanoes. They form when water is displaced. On volcanoes, this can occur via:
Subarmine eruptions
Collapse of part of a volcano into the sea
A lahar or pyrocloastic flow entering the water
This can then cause water to travel locally but ALSO GLOBALLY AND REGIONALLY.
110
What is the case study for a tsunami that was caused by a volcano?
1883 eruption of Krakatau, where a super volcano pyroclastic flow entered the ocean, causing numerous deaths and causing 36,000 deaths, which was a global impact.
111
Summarise how landslides and avalanches are hazards.
Are common and can be caused by both volcanoes and earthquakes. Debris avalanches tend to become channelled into valleys and can travel large distances well beyond their source areas, It is difficult to reduce the impact of debris avalanches because they occur without warning.
Mostly local effects.
112
List all of the volcanic hazards and on what scale the hazards can affect people.
Tephra: local/regional
Ash: local, regional, or global (Eyjafjallajökull)
Gases: Local
Lava flow: local
Pyroclastic flow - Local/regional
Lahars -Local/Regional
Jokulhlaups: Local
Tsunamis: Local, Regional, or Global
Landslides and avalanches: local
113
How many earthquakes are there per year? and how many are hazardous?
500,000, with 100 being hazardous
114
What is the focus and epicenter?
Focus: Where the seismic shock wave originates from
Epicentre: The point on the earth's surface directly above the foci.
115
What are the four seismic waves that are released from an earthquake or seismic event?
Primary waves: longitudinal and compressional waves (Sideways movement) Fastest, lowest frequency and goes through liquids and solids
Secondary waves are transverse waves, right-angled (vertical movement), half the speed of p-waves, and cannot travel through liquids.
Surface waves are across the surface and are slowest; they stay in the crust and have a low frequency.
Rayleigh waves (Surface wave): roll motion
Love wave (Surface wave): shear movement
116
How are earthquakes categorised using the depth of their focus?
Shallow-focused: These common earthquakes are shallow at the surface, at around 0-70km in depth. Conditions are cold, brittle crustal rocks, which results in fracturing due to stress
Deep-focused: 70–700 km depth means higher pressure and temperature, releasing higher energy seismic waves that result in powerful earthquakes. Mineral changes in the rocks and water content play a significant role in the release of energy during these earthquakes. But they dont have much imapct on the surface as they are so far down, the energy is lost by the time they reach further up towards the crust.
117
Where are four locations where earthquakes can happen?
1: Mid-ocean ridges (Sea floor spreading, tensional forces)
2: Ocean trenches and island arcs (Compressional forces)
3: Collision zones (Compressional forces)
4: Conservative plate boundary (Shear forces)
They can also occur anywhere, such as in old faults, former plate boundaries, the collapse of old mines, and the extraction of oil and gas.
118
How is the Richter scale used to measure earthquakes?
Is used to only indicate the damage an earthquake might cause. It uses the amplitude of the earthquake to determine the magnitude of the earthquake (size). It is a logarithmic scale, so each increase represents a 10-fold increase in the amplitude.
119
What other factors, apart from magnitude, can be used to determine earthquake damage?
Geographical location and geological setting
Level of development
Population density
Level of preparedness and planning
120
How is the Modified Mercalli Intensity (MMI) scale used to measure earthquakes?
Measure both earthquake intensity and impact, but this is a qualitative assessment based on observation. A value is assigned to a specific site after an earthquake, so it can be used to plot on an isometric map.
121
How is the Moment Magnitude scale used to measure earthquakes?
Increasingly, the moment magnitude scale takes preference. It measures the energy released more accurately than Richter, as it uses the physical movement caused by an earthquake as a direct function of energy.
122
What are the five main types of hazards caused by earthquakes?
1. Ground shaking or displacement
2. Liquefaction
3. Landslides/avalanches
4. Tsunamis
5. Flooding
123
Explain ground shaking and displacement (the hazards of earthquakes)
Ground shaking and displacement are the horizontal and vertical movements of the ground.
They cause hazards as infrastructure can collapse under horizontal movement due to their stability being affected by swaying. Ground movements displace rocks which can damage roads, tracks, pipes and buildings as well as affect public water suplies and groundwater.
124
What factors does the severity of ground shaking and displacement depend on?
Magnitude of the earthquake/intensity
Geology
Distance from epicentre
125
Explain liquefaction
When an earthquake occurs where the geology has a high water content and consists of fine-grained sands, alluvium, or is reclaimed from the sea, the seismic waves cause. It causes the fine grained material to act like a liquid which leads to building collapse and sinking. This happened in Christchurch, New Zealand 2011.
126
Explain how landslides and avalanches cause hazards (relating to earthquakes)
Earthquakes in mountainous regions often cause landslides and avalanches. Steep, unstable slopes are notoriously unstable and vulnerable to landslides. Their vulnerability is increased by deforestation and heavy monsoon rains, so that even small earthquakes can cause landslides. This happened in 2015, Ghorka, Nepal where landslides blocked rivers sparking flash foods, and avalanches occurred on Mt Everest
127
Give some background information on Indonesia (Merapi volcano)
Is an EDC
Population size = 256 million
Population density = 1.8 million km^2
Java island in particular = 1000/km^2 so more harm from hazard
HDI = 0.689
GDP = $11,400
Literacy rates = 93.9%
Doctors per 1000 = 0.2
Employment structure is mostly agriculture and manufacturing
128
Describe Indonesia's tectonic setting
Indonesia is an archipelago (island arc) created by a convergent plate boundary as 2 oceanic plates move towards each other
180 volcanoes in area
Widespread subduction along the 3000km island archipelago
Much of it is formed by the subduction of the indo-australian plate beneath the Eurasian at the java trench in the West
Towards the east, the continental shelf of Northern Australia collides with the Eurasian plate, producing a highly seismic area
The volcanos here are strato-volcanos
129
Describe and explain the 2010 Merapi eruption in Indonesia
- is a strato-volcano with a height of nearly 3km formed by the Australian plate subduction under the eurasian plate
It is one of 130
It is one of the most active erupting 68 times since 1548
Since 1920, 10 eruptions have caused fatalities
A dome collapsed creating a pyroclastic flow
Vei of 4
Explosive
Erupted until 12th November
130
Describe and explain the hazards of the 2010 Merapi eruption in Indonesia
Pyroclastic flows - significant damage to rainforest, farms, and buildings
CANGKRINGAN and KEMALANG were most affected
The pyroclastic flow was caused by a dome collapsing close to the summit
It flowed down towards the southeast
Lahars were triggered as it was the start of the rainy season. They followed the river channel and reached the city of YOGYAKARTA 35km away from the summit
CANGKRIGAM AND KEMALANG again were most affected due to the damage of rice fields and infrastructure.
Ash cloud reached 18km and fell 35km away from the summit reaching YOGYOKARTA laying on the ground 2-4 cm thick, which damaged 200 ha of forest
Closed air space
Buried infrastructure and farms
Poor breathing
Positive affect on fertility of soil
Sulphur dioxide - at higher altitudes, so2 reacts with rain, creating acid rain but is also an aerosol but does not have a global effect on climate. However, acid rain affected flights
Lava flows were slow due to andesitic lava being viscous
Didn't do much damage but created forest fires
131
What were the social, economical and environmental impacts of the Merapi eruption in 2010
Social
200000 people made homeless
320000 people displaced
Emergency tents set up but were too close to the volcano, so it had to be moved
278000 people had to flee
Evacuations crowded in the tents, creating poor sanitation
Lava flows, and Ash closed roads
5000 people were killed due to an earthquake 50km away
Economical
$450 million in damage for farming tourism and manufacturing industries
$13 million loss in agricultural produce
Mining and geothermal jobs lost on the volcano, so they had to sell sand and clean Ash, which reduced health
Tourism dropped by 30% for locals and 70% for international tourism
2500 flights cancelled
Decreased level of trust and security so no longer a trusted place for tourism
Environmental
Ash Rock and lava deposited on the sides of the volcano were washed down into towns and rainforests, creating lahars
Water supplies contaminated with Ash
But soils were fertilised, and global cooling saw advantages.
132
Why do people live near volcanoes in Indonesia and Merapi?
*Volcanoes cannot be prevented, so have to develop resilience
*Give people a place to live, as housing is usually cheaper near volcanoes, where they are more at risk.
*People People forced to live there due to high population densities (1000 people / km2)
*9% live below the poverty line with limited resources, so have little choice on where to live
*The agricultural industry is good near volcanoes due to weathered lava and ash as well as tropical conditions, so it has fertile soil.
*Steep-sided slopes of stratovolcanoes allow terraced farming
*Geothermal power: Sarulla, a 350 MW power station
*Mining for volcanic minerals such as sulphur used in many chemical products - East Java is extracted directly from the crater by workers
* Emotional attachment to the place: generation of family lived in these areas; cultural belief of volcanoes
133
Give some background information on Japan (Ontake volcano)
- Japan is an AC
-HDI = 0.903
-GDP = $40,800 / year
- Employment = Agriculture 3%, Industrial 23%, Services 73%
- Literacy rate: 99%
- Doctors per 1000 = 1.8
Population size: 127 million
- Population Density = 349 people / km^2
- Has 110 active volcanoes
- 70% is mountainous formed by volcanic activity
- Much of the folklore is dominated by volcanoes.
134
Describe Japan's tectonic setting
- Situated in the ring of fire
- 4 plates converge with widespread subduction (Eurasia, Pacific, Philippine, and North America)
- Created island arcs
- 1200 eruptions in the past 2000 years
- Most are VEI 1-4 but some are between 5 and 6
- VEI 2-3 occur every 4–18 years
- VEI 4-5 occur every 50-200 years however there is lots of variation so is random.
135
Describe and explain the 2014 Ontake eruption in Japan
- Was a strato-volcano
- Volcano is 300m tall, often covered in snow
- 200km west of Tokyo
- Been dormant for centuries but small eruptions were recorded in 1979 and 1980.
- Further smaller phreatic eruptions (Eruptions of steam from a volcano caused where ground water meets magma) in 1991 and 2007
- Popular for climbers and tourists
- Erupted without warning in 2014, there were some seismic activity but it was thought to be phreatic eruptions.
- Killed 63 people, was the first fatal eruption since 1991.
- Air space closed due to ash
136
What were the social, economic, and environmental impacts of the Ontake eruption in 2014?
Social
- Killed 63 hikers and climbers
- 200 survivors made it down but were injured
- Japanese prime minister sent the military to assist with rescues
- Air space closed due to ash cloud
Economic/political
- Ski resort business affected due to damaged reputation
- Tourism affected due to damaged reputation
- Agriculture damaged especially the crop "Hokusai." 18 ha of farmland damaged
- Takes 3x longer to prepare crops due to ash
- New laws - volcanic disaster caution zones where places would be considered at risk
- Farming sued the government demanding compensation for the loss of crops
137
State what modifying the event is
It involves changing and mitigating volcanic hazards to reduce loss of life
138
Why is modifying the event of volcanoes impractical?
Is hard to do and can only be used on lava flows, such as lava diversion, lava cooling. Furthermore can only be used in AC countries. Example is the Grindavik eruption 2023, where they used earth barriers to block the lava flow from going to the Geothermal power plants and blue lagoon. Also used lava cooling.
139
What are 2 other examples where modifying the event of volcanoes took place?
Indonesia: Very little done to modify the event, but sometimes will dredge river channels to prevent blockages and free flow of water
Italy: scale success with slowing and diverting lava flows from Etna. Earth barriers, large concreete blocks dropped into the lava flow, and channels to divert lava away from the settlement have been used in the past.
140
Why is there a difference in modifying the event in different countries?
Economic difference, Indonesia is an EDC but Italy is an AC, so will be able to afford schemes to modify the event.
141
What does the modification of vulnerability mean?
increasing the resilience of a community
142
How does Indonesia to modify the vulnerability?
- Community Preparation: Villagers on Southern slopes encouraged to relocate, CVHM was closely linked with the local government so helped advice mitigation strategies.
- Prediction and warning - Been able to upgrade instruments and monitor more than 60 volcanoes.
- Hazard-resistant buildings - Pitched roofs to stop ash from accumulating and caving in roofs.
- Land use zoning: Use hazard maps, splitting the land into three, Hazard Zone Three (Lava, ash, Pyroclastic flows), Zone Two (Pyroclastic flows and ash), Zone One (Lahars)
143
What does Italy do to modify the vulnerability?
Community Preparation: A well-established alert level understood by emergency services, governments and communities, as well as the proximity of airports
Prediction and warning: constant monitoring, e.g., seismonitors, tilt meters, analyses of gas emissions, ariel and satellite surveys, and infrared, are all carried out regularly to see any changes in volcanic activity.
Hazard-resistant buildings: research into effective building design to resist ash fall and secondary effects of volcanic activity such as earthquakes
144
How does Indonesia modify the losses compared to Italy?
Indonesia -
Limited resources
Temporary shelter in safe zones
Material removed from the modification of the event such as dredging is used as building material
Well equipped and trained emergency services
Italy -
Well timed evacuation planning, ability to compensate individuals and businesses effected by the volcano.
145
Give some background information on Japan (Tohoku Earthquake)
-Japan experiences 500 earthquakes every day, but they they are too small to have any effects.
-Japan has been hit by many high-magnitude quakes, which have had a huge impact on its people. Since 2000, 23 earthquakes of 7 Mw (Moment magnitude scale) have occurred in Japan causing 16,000 fatalities.
- AC
- 377,975 km^2
- 349 people / km^2
-$40,800 per capita
- HDI = 0.983
- 1.83 doctors per 1000 people
- Literacy rate of 99%
- 3% Agriculture, 23% industrial, 73% services
146
Describe Japans tectonic setting (Tohoku earthquake)
Movement along plate boundaries lying offshore of the Japanese mainland creates a risk of tsunamis.
The Pacific coastal zone is the most vulnerable, being densely populated (349 people per km2), so it is more at risk of flooding from tsunamis.
147
Summarise the earthquake of Japan (Tohoku earthquake)
-Pacific and North American plate
-Two days beforehand there were major tremors - 7.2 Richter Scale
-24km epicentre, 74km off the coast of Sendai
-Waves travelling along many interlinked fault systems for 500km
-This built up energy on the waves
-Horizontal crust displacement of the sea floor was measured at 50m
-Seabed rose 16m
-Ground shaking lasted 6 minutes
-20 minutes tsunami developed
-420 aftershocks at 5.0 Richter Scale
-Earth shifted axis by 2/5 cm
-Coastline dropped by 0.6m
-Undersea mega thrust
148
How long did the Tohoku earthquake last?
6 Minutes
148
How many aftershocks were there and what were their magnitudes?
420 aftershocks
5.0 magnitude
149
Explain how the earthquake occurred in Japan (Tohoku earthquake)
-Seabed displaced by 50m raised by 16m. It caused a tsunami an hour after the earthquake. The wave height was 10-15m.
-Reached the nearest coastline in 30–40 minutes.
-Hit the coast, causing erosion, 95% of vegetation destroyed, and 500 km^2 were inundated.
-Transported sediment 5km inland, deposited in paddy fields and forests. Some seawater evaporated on surface and salt crusts formed on the fields.
150
Summarise other factors that contributed to the high vulnerability of the Tohoku earthquake.
1. Very old oceanic crust, being cooler and denser thought would slide easily
2. Warping of the pacific plate gets stuck rather than sliding so strains
3. Coastline is tugged and waves were concentrated in bays
4. 70% Japan is mountainous
5. Soft reclaimed land is susceptible to ground shaking and landslides
151
What were the social impacts of the Tohoku earthquake?
-Killed 16,000
-Injured 6000
-90% of deaths due to drowning
-People near Fukushima nuclear power plant had to be evacuated
-Some communities had to be relocated from their original sites
-Some small coastal schools destroyed
-One school lost 78/108 students and 10/13 staff
-2/3 of the victims were older than 60
-100,000 children affected
-2000 children orphaned
-Many people spent years in temporary accommodations.
-Peoples whereabouts are unknown
-Traditional funerals waived off to reduce diseases
152
What were the economic impacts of the Tohoku earthquake?
-230,000 vehicles damaged
-4 ports destroyed
-Infrastructure, schools, hospitals, all damaged
-$181 billion in damage
-Still financial costs today and are still rebuilding
-Nuclear reactor decommissioned
-Stock market lost value
-4.4 million households and businesses lost electricity
-Bullet train washed away
153
What were the political impacts of the Tohoku earthquake?
-Government had to add money into the economy
-Nuclear power become a political issue - protests
154
What was an environmental impact of the Tohoku earthquake?
- Radioactive material leeched into the pacific.
155
Give some background information on Nepal (Gorkha Earthquake)
-Nepal is an earthquake-prone country
-On average, it receives two 7-8 Mw earthquakes every 40 years and one 8+ Mw every 8 years.
-Earthquakes records are much less complete in countries such as Japan or Indonesia and many seismic have gone unrecorded.
156
Describe Nepal's tectonic setting (Gorkha earthquake)
-Nepal is situated in a collision zone where the indo-australian plate meets the Eurasian plate As these plates grind past eachother, pressure builds up and energy is released as earthquakes
-The geological structure of valleys in Nepal increases seismic risk. Pre-historic lakes filled many of the valleys, and their legacy is hundreds of meters of soft sediment.
-In Kathmandu Valley, the depth of the sediment reaches 600m.
-Nepal is the 11th most earthquake-prone country in the world.
-GEOLOGY, URBANISATION AND BUILDING QUALITY ARE THE THREE MAIN RISK FACTORS IN NEPAL
157
What were the main causes of the Gorkha earthquake?
25th of April 2015, with a magnitude of 8 MW, and killed 9000 people
collision zone of the Indian and Eurasian plates, creating fold mountains. 50 ma, collided, causing shallow earthquakes (12 km) due to the subduction of the Indian plate. Energy moved 120km east, towards Kathmandu. Raised the land 1m and Everest sank 3cm
158
Why are earthquakes frequent in Nepal?
There are two major fault systems in the Himalayas.100-120km apart and 90% of all earthquakes occur between these.
159
How many aftershocks were in the Gorkha earthquake and what were their magnitudes?
300 aftershocks over 6 weeks. Ranging from 4-6.7 Mw. Major 7.3 Mw on 12th may 2015 killing 200 and injuring 2500
160
What were the effects of landslides in the Gorkha earthquake?
Increased general instability of slopes and landslides were the main obstructions to rescue.
Triggered by tremors and monsoon rains,.
Many villages buried
Longtang village experienced a pressure wave that blasted an avalanche 2-3 km wide of snow. Killed 300 people.
250 people killed under a mudslide
Lapark, completely destroyed
Landslides were not as severe as expected
Earthquake happened after monsoon 5, so the land was wet and not resistant to slippage
-Rocks stronger than expected
161
What were the effects of flooding in the Gorkha earthquake?
Landslides block rivers creating floods upstream but when debris collapses without warning. Lakes can drain suddenly, causing a flash food. Kali Gandaki river was dammed and created a lake that flooded all homes 1km upstream.
162
What were the social impacts of the Gorkha earthquake?
8800 killed
22,000 injured
20 climbers killed on Everest in an Avalanche
2.8 million displaced in Kathmandu valley
473,000 houses destroyed/damaged
1 million required food assistance
Increase in trafficking women from poorest families, who were homeless
Feld unevenly by different ethnic groups
Gender inequality when it came to aid
Culturally important locations damaged by the earthquake such as the 9 story tower Dharahara tower
163
What were the economic impacts of the Gorkha earthquake?
Lack of reliable data
1 of the poorest countries
Estimated cost $10 billion
Tourism (10% of economy) badly hit
Everest climbing season closed in 2015
$200 million from Asian development bank for reconstruction
Debt incresed
Planting senega disrupted
Longer term impact in food security
164
What were the political impacts of the Gorkha earthquake?
Nepal was politically unstable before the earthquake
A period of turmoil included assassinations and coups, showed signs of moving but the earthquake happened
Nepal received emergency aid for longer term construction
International aid created tension with India which accused of trying to use its humanitarian aid as a way of self-promotion within the region
165
Why is modifying the event for an earthquake not really convenient or possible?
Harder to predict but ground shaking and landslides can only really be managed
166
How was the vulnerability modified in the Gorkha earthquake in Nepal?
Education: programs and earthquake awareness day
Community preparation: Encouraging households to have a go-bag containing items useful in an earthquake
Hazard-resistant buildings: Building codes and regulations were introduced, such as tires with sand or gravel to absorb shockwaves
Land-use zoning - Mapping high risk shake zones
167
How was the vulnerability modified in the Tohoku earthquake in Japan?
Education: Education and training for all ages
Prediction an warning: JMA providing warnings on tsunamis and ETAs of them
Hazard-resistant buildings: Fire proofing wooden buildings and aseismic design "Soft story"
Land use zoning: Assemble places after earthquakes
168
How did Japan and Nepal modify the losses of the two earthquakes (Tohoku and Gorkha)
Nepal - Hasn't got the resources to recover from the earthquake, but did get aid from international organisations such as the EU and the UN.
Japan - Has the resources to recover the losses as well as well-rehearsed recovery and reconstruction plans
169
What is the disaster risk equation and what is it used for?
Risk = (Hazard x Vulnerability) / capacity to cope and adapt
Is used as a qualitative tool to see the relationships between different components of risk and what makes a hazard so disastrous.
170
What can the hazard of the disaster risk equation be split up into?
1. Type of hazard (Geophysical, climatological, meteorological hydrological, biological)
2. Magnitude of the event (How powerful)
3. Frequency of the event (How often it occurs)
171
What is a hazard profile?
A graph that is used to compare two places and the hazards. These profiles use 5 variables to depict the hazard and provide with information about the nature of the hazard.
172
What is the relationship between frequency and magnitude of events?
Inversely proportional - there is a strong correlation between magnitude and frequency as the greater the magnitude, the less frequent they are.
173
What does the vulnerability relate to in the disaster risk equation?
Relates to the susceptibility of a society to damage and withstand exposure to and from risks from a hazard.
174
What are 6 variables that affect the vulnerability of a population?
1. Population total, density and structure
2. Proximity to the hazard.
3. Economic development
4. Political stability
5. Infrastructure
6. Education
175
What does the vulnerability quadrant show ?
The graph depicts how different areas can change in vulnerability. An area such as the UK is likely to have a greater understanding of the risks making the population less vulnerable.
176
What does the capacity to cope (resilience) relate to in the disaster risk equation?
Refers to a persons or groups ability to deal with and bounce back from adversity. Often covers similar ideas to the vulnerability.
177
What are 5 factors that affect a places capactity to cope?
1. Economic development (Money)
2. Access to aid
3. International relationships
4. Debts
5. Population structure
178
What is the disaster response curve (park model)?
Shows the relationship between quality of life and time. Immediately after a disaster, quality of life drops due to the vulnerability and the hazard. The capacity to cope determines how quickly the quality of life can return to normal. Sometimes it may even go above the normal as buildings may be rebuilt to a higher standard.
179
What does the curve depend on and what does the rate at which the quality of life deteriorates depend on in the disaster response curve (park model)?
The shape depends on the type of hazard
The rate at which quality of life returns to normal however is based on physical and human factors
Physical
Magnitude and type of hazard
Speed of onset of event
How long the events last
Human
Level of monitoring
Degree of preperation
Quality and quantity of relief and aid
180
How do impacts of disasters vary?
According to their levels of development
For richer countries, there are high financial losses while poorer countries are left with severe shocks to the community, welfare, and infrastructure. The poor are also vulnerable to secondary hazards such as diseases.
Poor economies as well can stop the growth of development and potentially destroy economic systems.
180
What is the pressure and release model (PAR) ?
Propose what should be done if the disaster is to be resolved.
Vulnerabilities are the major factor that can be controlled to prevent disasters from occurring.
181
What is the risk perception model?
When their is awareness. of risk, people's responses are determined by action and learning thresholds. The level of reaction depends on hazard experiences, capability of an individual, and the capacity to cope
If potential losses are too great action is taken place to mitigate risk so people can stay at a place with more confidence
However, if people perceive the risk being too great, it may lead to relocation
182
How does peoples attitude towards risk vary?
-Ignorant of risk such as volcanoes being dormant
In this situation people absorb any losses when the eruption happens such as in Indonesia
-Accept and share the losses may happen if people cant afford to move so accept the losses and share them with the community
-Search for effective adjustments when people are aware of the risk and want to change or can relocate
183
What are some designs of infrastructure to modify the vulnerability?
Creation of a flexible foundation
Counter forces with dampening
Shield buildings from vibrations
Reinforce the buildings structure using cross-bracing
Earthquake-resistant building materials.
Structural regularity and symmetry
Strong connectivity between different structural elements, ie walls and floors
Ease to exit
Fire resistant
184
What are hazard maps?
Identify areas at risk from volcanic hazards
