Tectonic Hazards Flashcards
(175 cards)
1
Q
What are the 3 types of material that can be ejected from a volcano?
A
Gas
Solids
Liquids
2
Q
Examples of gas to be ejected from a volcano?
A
Carbon monoxide
Hydrogen sulphide
Sulphur dioxide
Chlorine
3
Q
Examples of solids to be ejected from the volcano?
A
Ash, dust, glassy cinders
Blocks of solidified
Pumice stone
4
Q
Examples of liquids ejected from a volcano?
A
Lava bombs- tephra or pyrolasts.
Which solidify in air- eg pumice
5
Q
Who was the first to consider the structure of the Earth and when?
A
The Greek philosopher Plato
2000 years ago
6
Q
Who came up with the first theory, when and what was it?
A
Edmund Halley
1692
The earths structure was made of hollow spheres
7
Q
What shape is the earth?
A
A geoid
Bulged around the equator and flatter at the poles
8
Q
Why is the earth shaped the way it is?
A
Due to centrifugal forces.
These are generated by the earths rotation, this forces the molten interior outwards
9
Q
Description of the crust.
A
Thin-
5-10m beneath the oceans to nearly 70km beneath the continents
10
Q
What are the two types of crust?
A
Oceanic and continental
11
Q
Description of oceanic crust?
A
Broken layer of basalt rocks
Sima- made up of silica and magnesium
12
Q
Description of continental crust?
A
Bodies of granite rocks
Sial- silica and aluminium
13
Q
Difference between Sima and Sial?
A
Sial is much thicker and less dense.
14
Q
What is the lithosphere?
A
What the crust and upper mantle makes up.
Where tectonic plates are formed.
15
Q
Description of the mantle?
A
Widest section- 2900km
Silicate rocks are in a thick liquid state which becomes denser the deeper you go.
16
Q
Why is the mantle a liquid state?
A
Due to the great heat and pressure within this zone.
17
Q
What is the asthenosphere?
A
A layer of softer almost plastic like rock.
Moves slowly carrying the lithosphere on top.
18
Q
Describe the core temperature?
A
Centre and hottest part- above 5000 degrees C
19
Q
What is the core made from?
A
Iron and Nickel
20
Q
Is the core more dense than the crust?
A
Yes the core is 4 times denser than the crust
21
Q
How many parts make up the core?
A
2- outer and inner
22
Q
Describe the inner core?
A
Solid and made up of an iron nickel alloy
23
Q
What is thought to create the earths magnetic field?
A
The spinning of the liquid outer core when the earth rotates
24
Q
Describe the outer core?
A
Semi liquid and consists mostly of iron
25
What does the cores heat generate?
Convection currents in the mantle that spread very slowly within the asthenosphere.
26
What causes convection currents?
Radioactive decay of elements in mantle and core- e.g Uranium
27
How do the convection currents cause movements?
The current in the asthenosphere create drag on the base of the tectonic plate.
28
How is new crust created?
When convection currents diverge. Magma plumes rise and cool to form new crust.
29
Describe sea floor spreading?
When convection currents diverge beneath an oceanic plate. It created structures called mid-ocean-ridges. Ridges of higher terrain on either side of the margin. Eg- mid Atlantic ridge.
30
Describe mid-ocean ridges?
Chains of submarine mountain ridges with regular transform faults across the ridges at right angles to the boundary. Can rise up to 4000m.
31
Alfred Wegner info
In 1912 proposed continental drift
Pangea
Based theory on geological evidence and fossil records.
Couldn't back up with a mechanism
32
When did more plate tectonics theory come to light?
1950's- palaeomagnetism
| 1960's- sea floor spreading
33
Geological evidence example 1
Glacial deposits and striations (rock scratches) in Brazil match those in west Africa
34
Geological evidence example 2
Matching rock sequences of age and composition linking Scotland and Canada.
35
How does geological evidence support continental drift?
These rocks and mountains must've formed under the same conditions to match- this would only be possible if the continents were once joined
36
Evidence for Continental drift?
Geological
Climatic
Biological
Jigsaw
37
Fossil record example?
Mesosaurus (reptile) found in Brazil and South west Africa.
| Glossopteris (plant) found in South America, Africa, India and Australia.
38
Living species example?
Earthworms from the same family found in New Zealand, parts of Asia and North America.
39
Climatic example?
Coal which is only formed under warm wet conditions has been found beneath the Antarctic ice cap. This can only be explained by Antarctica being once positioned in warmer latitudes.
40
Process when oceanic plate combines with continental?
Subduction
41
Which plate is denser?
The oceanic plate
42
Which plate subducts?
The oceanic plate
43
Where is the exact point of collision at a destructive margin?
The bending of the oceanic plate- deep open trench
44
Give an example of a deep ocean trench?
Peru- Chile trench along the Pacific Coast of South America
45
What happens to the continental plate when it meets an oceanic plate?
The continental land mass is uplifted, compressed and buckled and folded into chains of fold mountains
46
Example of fold mountains?
Andes
47
What happens to the oceanic plate after subduction?
Melts at depths beyond 100km and completely destroyed by 700km.
48
Where is the zone where melting occurs of the oceanic plate?
Benioff zone
49
What is the melting of the oceanic plate caused?
Increasing heat at depth and the friction between the plates
50
What may friction create?
Tension and stresses building up, may be released as deep focus earthquakes
51
What happens to the oceanic plate once it's been melted?
Creates magma- less dense than the asthenosphere
Rises in plumes
Through faults in the buckled plate
52
What occurs when two oceanic plates meet?
The faster of denser subducts
53
What is formed when two oceanic plates meet?
Deep ocean trench
| Rising magma from Benioff zone forms crescents of submarine volcanoes which may form Island arcs
54
Give an example of a trench formed by two oceanic plates colliding?
Marinas trench
| Pacific subducts under Philippine
55
Why does subduction not occur when two continental plates meet?
Both plates are of lower density than the asthenosphere beneath them
56
What is formed when two continental plates meet?
Sediment between them becomes uplifted and buckle to form high fold mountains.
57
Example of a fold mountain?
Himalayas
58
What else occurs when 2 continental plates collide?
Shallow focus earthquakes
59
Describe a conservative plate margin?
Friction
Stress builds when sticking occurs.
Stresses released as shallow focus earthquakes
60
Example of a conservative margin?
San Andreas fault
61
Earthquake example along the San Andreas fault?
LA Northridge 1994
62
What are the two kinds of plate divergence?
Oceanic- sea floor spreading
| Continental- rift valleys
63
How are rift valleys formed?
Lithosphere stretches, fractures into parallel faults
64
Describe rift valleys?
Sets of parallel faults
| The land between the faults collapse into deep, wide valleys which are separated by upright blocks of land called horsts
65
How are hotspots formed?
Concentrated decay in the core. Localised thermal currents- plumes rise vertically.
Plumes burn through the lithosphere
Movement of plate results in chain
66
Facts about Hawaii?
Pacific plate moves north west at a rate of 5-10cm per year
| Shield volcanoes- runny lava
67
Benefits of volcanoes?
Lava flows create new land
Geothermal power from hot rocks
Igneous rocks contain valuable minerals- gold, silver, copper and diamonds
68
What are the 3 intrusive volcanic features?
Dykes
Sills
Laccoliths- batholiths
69
Describe dykes?
Where the magma solidifies in a fissure (vertical crack)
70
What can dykes form?
More resistant- prominent wall like features
| Less resistant- ditch like features
71
What are sills?
When magma solidifies into horizontal or in between layers of pre-existing rock
72
What is a laccoliths and batholiths?
When viscous magma forces the overlying rock strata or layers into a dome
73
Causes of tsunamis?
Seismic activity generated by ocean floor earthquakes or submarine volcanic eruptions.
This displaces a large volume of water
Causing a series of waves
74
What is the wave height of tsunamis?
Low- less than 1m
| Increase to over 25m upon reaching the shore
75
What is the wavelength of tsunami's?
Very long
| 100-1000km
76
What speed do they travel at?
640-960 km
77
Is the first wave the biggest?
Not always
78
What is the wave period?
Between 10-60 minutes
79
Where do most tsunami's occur?
90% in the Pacific Ocean
80
Different types of lava at which margins?
Basaltic at Constructive
| Andesitic and rhyolitic at destructive
81
Describe basaltic lava?
Iron and magnesium
Low in silica
Fluid and free flowing
82
Describe acidic lava?
Rich in silica
Viscous
Violent eruptions as gas cannot escape
83
Four main types of volcanoes?
Dome
Caldera
Shield
Fissure
84
Describe dome volcanoes?
At destructive margins
Acidic lava
Steep sided
Eg- puy de dome in France
85
Describe caldera?
Central part of volcano has collapsed
Very wide circular crater
Destructive margins
Acidic lava
86
Describe a shield volcano?
Gently sloping sides
Occur at hotspots or constructive margins
Basaltic lava
87
Describe a fissure volcano?
Long linear vent
Fairly flat surface
Constructive
Basaltic lava
88
Hot spring fact file
```
Groundwater emerges from surface
Water is heated by volcanic activity
Temperatures upto 90 degrees
Water has a high mineral content
Eg- North Island New Zealand
```
89
Geothermal features
Hot spring, geysers and mud pools
90
Geysers
Hot water and steam ejected through faults in the rock
Groundwater is heated to above boiling point
Hot water becomes pressurised
Eg- Old Faithful- Yellowstone
91
Mud pools?
Form in areas with very fine- grained soil.
The hot spring mixes with the soil
Eg- Yellowstone and Iceland
92
Impacts of volcanoes?
Lava flows burn crops
| Ash fall buries crops and creates air pollution- breathing difficulties
93
How are mid ocean ridges formed?
By sea floor spreading
| Diverging plates
94
How are rift valleys caused?
Stretching and collapsing of the crust
| Diverging continental plates
95
How do mid ocean ridges cause earthquakes?
Sections may widen at different rates and times. This leads to frictional stress building up.
Released as a shallow focus earthquake
96
Describe mid ocean ridges?
Can rise up to 4000m
Middle are marked by deep rift valleys
Over time the rift valleys widen due to magma rising from the aesphenosphere and solidifying as new crust.
97
What are horsts?
The upright blocks that separate the valleys in rift valleys
98
How was the Great African Rift Valley formed?
Magma from the asthenosphere rising to heat the overlying plates which expand and bulge to create horsts. Eg- Ethiopian highlands
As the heating plate is stretched it causes it to fracture along fault lines.
This leads to fallen blocks of lowland called grabens
99
Describe a Rift Valley?
Land between the faults collapse in deep, wide valleys
100
What a grabens?
Blocks of fallen lowland
101
Different types of eruptions?
```
Icelandic
Hawaiian
Strombolian
Vulcanian
Vesuvian
Peléean
Plinian
```
102
Background info on Montserrat.
Popular holiday destination for rich and famous
Island arc formed where the Atlantic plate subucts beneath the Caribbean plate
Most of the island are composite volcanoes
Island is 16KM long and 10KM wide
103
Eruption details? Montserrat
Eruption on 25th June 97
Dome of volcano collapsed
Sending 5 million cubic metres of hot rock down the Soufriére hills to
South of island covered by pyroclastic flows of hot ash, mud and rock
104
Montserrat preparation?
Exclusion zones- safe and evacuation zones
August 1995- south of island evacuation to churches and halls in the north.
April 96- the entire population of Plymouth was forced to leave
105
What were the immediate effects of Montserrat?
19 deaths from fires associated with deaths from pyroclastic flows. Many burn and inhalation injuries
2/3 of all houses were either buried by ash or flattened by rock.
Farmland and 3/4 of infrastructure destroyed
106
Has Chances peak erupted since?
In 2010 chances peak explosively erupted
107
Immediate responses to the Montserrat eruption?
The Montserrat volcano observatory was set up in 1995.
Red Cross set up temporary schools and provided medical support and food
Warning systems were set up- speakers, sirens
USA and British navy troops carried out evacuation
£17 million from you UK govt
108
Long term responses? Montserrat
3 year redevelopment programme for schools, houses and medical services
Young people moved away- leaving an ageing population
109
What eruption is etna? How has it been caused?
Strombolian
| Collision of African and Erasion plates- linked to rifting
110
Impact of Mt Etna eruption?
Lava destroyed springs with supply water to Zaffefena- town of 8000 people
Several people lost homes and farmland
111
Management of Etna?
```
Lava diverted away from Zafferena.
First earth barriers with were overcome
Explosives used to divert flow into a man made channel
Concrete blocks to plug lava
1991-1993
```
112
Immediate effects of earthquakes?
Ground shaking destroys infrastructure and buildings
Immediate deaths and injuries from crushing
Liquefaction
Landslides caused by slope failure
113
Secondary effects of earthquakes?
Fires caused by broken gas pipes
Injuries may result in long term disability
Power cuts restrict emergency services
Dead bodies will spread disease such as Cholera
114
What influences the consequence of the Earthquakes.
```
Magnitude
Depth
Location of epicentre
Pop density
Education
Building strength
Time of day
```
115
Earthquake prediction?
```
Micro quakes
Ground bulging
Magnetic changes within rock
Increased argon content in soil
Curious animal behaviour
```
116
Features of an earthquake proof building?
Rolling weights on roof to counteract shock waves
"Birdcage" interlocking steel frame
Reinforced foundations deep in bedrock
Rubber shock absorbers between foundations
117
Other planning for earthquakes?
Designed infrastructure to withstand shaking
GIS can be used to prepare hazard maps to show areas of great risk
Public education- earthquake drills
118
What term is used to describe planning for hazards?
Contingency planning
119
Socio-economic effects of Hati earthquake 2010?
230,000 to 250000 lives lost, many due to building collapse
50% of building collapsed- inc Parliament and Police headquarters
Capital flattened
1.5 million homeless
Infrastructure- main port and roads
120
Environmental effects of Hati 2010?
Liquefaction- building foundations subsided
Ground slumping
Small localised tsunami- killed 7
Landscape permanently disfigured- corals pushed upwards and farmlands collapsed
121
How many people died in Christchurch?
185
122
What happened in l'aquila in 2002?
A 5.5 quake caused a primary school to collapse despite being built to 'national standards'
123
Hazards associated with volcanoes?
Pyroclastic flow
Dust emissions seed torrential rainfalls resulting in mud lahars
Flooding results from volcanic debris blocking rivers
124
Which eruptions have basaltic lava?
```
Icelandic
Hawaiian
Strombolian
Vulcanian
Vesuvian
```
125
Which eruptions have rhylotic lava?
Vulcanian
Vesuvian
Peléean
Plinian
126
Which eruptions are andesitic?
Vulcanian
Vesuvian
Peléean
127
Characteristics of Icelandic eruption?
Lava flows gently from fissures
128
Characteristics of Hawaiian eruption?
Lava flows gently from a central vent
129
Characteristics of a Strombolian eruption?
Frequents explosions of tephra and steam. Occasional, short lava flows
130
Characteristics of Vulcanian eruption?
Less frequent, but more violent eruptions of gases, ash and tephra
131
Characteristics of a vesuvian eruption?
Following long periods of inactivity, very violent has explosions blast ash high into the sky
132
Characteristics of peléean of eruptions?
Very violent eruptions of nuées ardentes
133
Characteristics of Plinian eruptions?
Exceptionally violent eruptions of gases, ash and pumice. Torrential rainstorms cause lahars.
134
Definition of a dormant volcano?
Has not erupted within historic times. More than 10,000 years is extinct
134
Montserrat warning signs?
July 1995- volcano began to erupt ash and dust.
| Scientists began to monitor gases, microquakes and changes in the volcano shape.
135
Describe palaeomagnetism?
Every 400,000 years the Earths magnetic field switches polarity. Particles of iron oxide in the ocean floor records the magnetic orientation of that time.
The older lavas were further away from the ridge.
136
Different types of Seismic waves?
Primary- fastest, compressions, can travel through all
Secondary- half as fast, shake, through crust and mantle only
Surface- slowest, cause most damage
Rayleigh- low frequency rolling motion
137
Mercalli scale?
Imperceptible
Moderate
Destructive
Catastrophic
138
How are earthquakes caused?
Stress builds in lithosphere due to friction.
| When stress is overcome, fractures cause faults. This sends seismic shockwaves to the surface.
139
Difference between focus and epicentre?
Focus is the breaking point of the earthquake.
| Epicentre is the point on the surface directly above the focus.
140
What effects the nature of the hazard?
```
Frequency
Warning signs?
Magnitude
Duration
How large an area did it effect
```
141
What makes a population vulnerable?
```
Population - density
Economic
Land use
Emergency services
Type of population
Hazard proof buildings
```
142
Strategies to manage volcanoes?
```
Exclusion zones
Emergency shelters
Drills/ sirens
Use of media
Emergency services
```
143
Fumarole?
Outlets of steam and gas
Gas can be carbon dioxide and monoxide
Solfatara when sulphurous gas- Naples
144
Define natural hazard?
A natural hazard is a threat of a naturally occurring event that will have a negative effect on people or the environment. Many natural hazards are interrelated, e.g. earthquakes can cause tsunamis and drought can lead directly to famine.
145
How many people are at risk from Etna?
900,000
146
Years when Etna erupted?
1991- 1993
2001
2002
2009
147
Sea floor spreading?
American geologist studied ages of rocks. Oldest rocks nearer to coast to USA and Caribbean.
Rate of 5cm a year
148
Features with Constructive margins?
New crust and basaltic rocks
Mid-ocean ridges
Shallow focus earthquakes
Submarine volcanoes
149
Features with destructive?
Deep ocean trenches
| Island arcs- two oceanic
150
Example of deep ocean trench?
Peru- Chile trench along the Pacific coast of South America
151
Describe Hawaii?
Pacific plate moves- 5-10cm a year
Shield volcanoes
Pahoehoe and blocky aa lava common
Mauna Loa
152
What happens to Hawaii when moves away from hotspot?
Lava becomes more Alkali, cinder cones may appear
| Steep sided cones associated with pyroclastic flows
153
Secondary effects of Haiti?
```
Strong aftershocks- 6.1
Government crippled
Inflation in food prices
Prison destroyed- lawless
Cholera kills- 1500
```
154
Immediate responses to Haiti?
International search teams- UN
US military distributed aid
16,000 UN troops to restore order
UN world food programme
155
Long term Haiti responses?
$11.5 billion reconstruction package
farming reform
Life safe building codes- locals employed as builders
156
Difference in price of traditional and life safe buildings?
Cost 15% more
157
When did l'aquila occur?
2009
158
Cause of Haiti?
Strike- slip fault
| Carribean and North American plate
159
Factors of Haiti earthquake?
```
In late afternoon 16.53
Magnitude 7
Shallow focus- 13km
Epicentre- 24km from Port-au-prince
70% pop on less than $2 per day
```
160
Causes of l'Aquila?
African plate pushing north on Eurasian plate
| Slip fault line underneath mountain range
161
Factors of L'Aquila earthquake?
Occurred at half 3 in the morning
Epicentre 7km from l'Aquila
300 aftershocks
Shallow focus- 10km
162
Impacts of l'Aquila?
```
305 deaths- died in sleep
Thousands homeless- 34,000 in tents
Historic capital badly affected
Architectural building destroyed
10,000 building altogether
Roman baths and medieval villages
```
163
Responses of l'Aquila? I
Rescue efforts haulted by Aftershocks
People still in temporary accommodation 3 years later
Rebuilding programme- $16 billion
164
Countries effected by Boxing Day
Indonesia, Thailand and Sri Lanka
165
Deaths and missing after Boxing Day?
Total- 290,000
| Indonesia- 236,000
166
Cause of Boxing Day?
Indo- Audtrailian plate pushing north under Eurasian plate
| Ocean floor pushed up several metres
167
Secondary affects of Boxing Day!
500,000 homeless refugees
44% lost livelihoods in fishing/ agriculture and tourism
Thailand loss of fishing industry- £226m
Negative multiplier effect
Water supplies contaminated by salt water
168
Immediate responses of Boxing Day?
160 aid organisations
| Australian Air Force
169
Long term responses to Boxing Day?
Tourist facilities prioritised
Education in schools and practice drills
Reconstruction- thousands homeless years later
Political barriers and tension
170
Background to Japan 2011?
9 magnitude earthquake
2011
North American plate caused Pacific plate to slip upwards 10m
Japan's warning system gave minutes to escape
10waves, overwhelmed tsunami defence walls
171
Primary impacts? Japan 2011
Building collapsed or set ablaze- broken pipes
Flooded 500 square km
Skyscrapers shook not collapse
25,000 dead or missing
172
Secondary effected? Japan 2011
Half a million homeless
Millions of homes without water and electricity
Shortages of food and medicine
Power plant threat of Nuclear disaster due to radiation leaks
173
Intermediate responses of Japan 2011?
Helicopters from rooftops
No looting or violence reported
Exclusion zones set up
Survivors huddles in shelters
174
Long term responses in Japan?
High repair bill for govt and private companies
| Defence wall effectiveness questioned
