Flashcards in Tectonic Hazards Deck (175):
What are the 3 types of material that can be ejected from a volcano?
Examples of gas to be ejected from a volcano?
Examples of solids to be ejected from the volcano?
Ash, dust, glassy cinders
Blocks of solidified
Examples of liquids ejected from a volcano?
Lava bombs- tephra or pyrolasts.
Which solidify in air- eg pumice
Who was the first to consider the structure of the Earth and when?
The Greek philosopher Plato
2000 years ago
Who came up with the first theory, when and what was it?
The earths structure was made of hollow spheres
What shape is the earth?
Bulged around the equator and flatter at the poles
Why is the earth shaped the way it is?
Due to centrifugal forces.
These are generated by the earths rotation, this forces the molten interior outwards
Description of the crust.
5-10m beneath the oceans to nearly 70km beneath the continents
What are the two types of crust?
Oceanic and continental
Description of oceanic crust?
Broken layer of basalt rocks
Sima- made up of silica and magnesium
Description of continental crust?
Bodies of granite rocks
Sial- silica and aluminium
Difference between Sima and Sial?
Sial is much thicker and less dense.
What is the lithosphere?
What the crust and upper mantle makes up.
Where tectonic plates are formed.
Description of the mantle?
Widest section- 2900km
Silicate rocks are in a thick liquid state which becomes denser the deeper you go.
Why is the mantle a liquid state?
Due to the great heat and pressure within this zone.
What is the asthenosphere?
A layer of softer almost plastic like rock.
Moves slowly carrying the lithosphere on top.
Describe the core temperature?
Centre and hottest part- above 5000 degrees C
What is the core made from?
Iron and Nickel
Is the core more dense than the crust?
Yes the core is 4 times denser than the crust
How many parts make up the core?
2- outer and inner
Describe the inner core?
Solid and made up of an iron nickel alloy
What is thought to create the earths magnetic field?
The spinning of the liquid outer core when the earth rotates
Describe the outer core?
Semi liquid and consists mostly of iron
What does the cores heat generate?
Convection currents in the mantle that spread very slowly within the asthenosphere.
What causes convection currents?
Radioactive decay of elements in mantle and core- e.g Uranium
How do the convection currents cause movements?
The current in the asthenosphere create drag on the base of the tectonic plate.
How is new crust created?
When convection currents diverge. Magma plumes rise and cool to form new crust.
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.
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.
Alfred Wegner info
In 1912 proposed continental drift
Based theory on geological evidence and fossil records.
Couldn't back up with a mechanism
When did more plate tectonics theory come to light?
1960's- sea floor spreading
Geological evidence example 1
Glacial deposits and striations (rock scratches) in Brazil match those in west Africa
Geological evidence example 2
Matching rock sequences of age and composition linking Scotland and Canada.
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
Evidence for Continental drift?
Fossil record example?
Mesosaurus (reptile) found in Brazil and South west Africa.
Glossopteris (plant) found in South America, Africa, India and Australia.
Living species example?
Earthworms from the same family found in New Zealand, parts of Asia and North America.
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.
Process when oceanic plate combines with continental?
Which plate is denser?
The oceanic plate
Which plate subducts?
The oceanic plate
Where is the exact point of collision at a destructive margin?
The bending of the oceanic plate- deep open trench
Give an example of a deep ocean trench?
Peru- Chile trench along the Pacific Coast of South America
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
Example of fold mountains?
What happens to the oceanic plate after subduction?
Melts at depths beyond 100km and completely destroyed by 700km.
Where is the zone where melting occurs of the oceanic plate?
What is the melting of the oceanic plate caused?
Increasing heat at depth and the friction between the plates
What may friction create?
Tension and stresses building up, may be released as deep focus earthquakes
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
What occurs when two oceanic plates meet?
The faster of denser subducts
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
Give an example of a trench formed by two oceanic plates colliding?
Pacific subducts under Philippine
Why does subduction not occur when two continental plates meet?
Both plates are of lower density than the asthenosphere beneath them
What is formed when two continental plates meet?
Sediment between them becomes uplifted and buckle to form high fold mountains.
Example of a fold mountain?
What else occurs when 2 continental plates collide?
Shallow focus earthquakes
Describe a conservative plate margin?
Stress builds when sticking occurs.
Stresses released as shallow focus earthquakes
Example of a conservative margin?
San Andreas fault
Earthquake example along the San Andreas fault?
LA Northridge 1994
What are the two kinds of plate divergence?
Oceanic- sea floor spreading
Continental- rift valleys
How are rift valleys formed?
Lithosphere stretches, fractures into parallel faults
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
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
Facts about Hawaii?
Pacific plate moves north west at a rate of 5-10cm per year
Shield volcanoes- runny lava
Benefits of volcanoes?
Lava flows create new land
Geothermal power from hot rocks
Igneous rocks contain valuable minerals- gold, silver, copper and diamonds
What are the 3 intrusive volcanic features?
Where the magma solidifies in a fissure (vertical crack)
What can dykes form?
More resistant- prominent wall like features
Less resistant- ditch like features
What are sills?
When magma solidifies into horizontal or in between layers of pre-existing rock
What is a laccoliths and batholiths?
When viscous magma forces the overlying rock strata or layers into a dome
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
What is the wave height of tsunamis?
Low- less than 1m
Increase to over 25m upon reaching the shore
What is the wavelength of tsunami's?
What speed do they travel at?
Is the first wave the biggest?
What is the wave period?
Between 10-60 minutes
Where do most tsunami's occur?
90% in the Pacific Ocean
Different types of lava at which margins?
Basaltic at Constructive
Andesitic and rhyolitic at destructive
Describe basaltic lava?
Iron and magnesium
Low in silica
Fluid and free flowing
Describe acidic lava?
Rich in silica
Violent eruptions as gas cannot escape
Four main types of volcanoes?
Describe dome volcanoes?
At destructive margins
Eg- puy de dome in France
Central part of volcano has collapsed
Very wide circular crater
Describe a shield volcano?
Gently sloping sides
Occur at hotspots or constructive margins
Describe a fissure volcano?
Long linear vent
Fairly flat surface
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
Hot spring, geysers and mud pools
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
Form in areas with very fine- grained soil.
The hot spring mixes with the soil
Eg- Yellowstone and Iceland
Impacts of volcanoes?
Lava flows burn crops
Ash fall buries crops and creates air pollution- breathing difficulties
How are mid ocean ridges formed?
By sea floor spreading
How are rift valleys caused?
Stretching and collapsing of the crust
Diverging continental plates
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
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.
What are horsts?
The upright blocks that separate the valleys in rift valleys
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
Describe a Rift Valley?
Land between the faults collapse in deep, wide valleys
What a grabens?
Blocks of fallen lowland
Different types of eruptions?
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
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
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
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
Has Chances peak erupted since?
In 2010 chances peak explosively erupted
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
Long term responses? Montserrat
3 year redevelopment programme for schools, houses and medical services
Young people moved away- leaving an ageing population
What eruption is etna? How has it been caused?
Collision of African and Erasion plates- linked to rifting
Impact of Mt Etna eruption?
Lava destroyed springs with supply water to Zaffefena- town of 8000 people
Several people lost homes and farmland
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
Immediate effects of earthquakes?
Ground shaking destroys infrastructure and buildings
Immediate deaths and injuries from crushing
Landslides caused by slope failure
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
What influences the consequence of the Earthquakes.
Location of epicentre
Time of day
Magnetic changes within rock
Increased argon content in soil
Curious animal behaviour
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
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
What term is used to describe planning for hazards?
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
1.5 million homeless
Infrastructure- main port and roads
Environmental effects of Hati 2010?
Liquefaction- building foundations subsided
Small localised tsunami- killed 7
Landscape permanently disfigured- corals pushed upwards and farmlands collapsed
How many people died in Christchurch?
What happened in l'aquila in 2002?
A 5.5 quake caused a primary school to collapse despite being built to 'national standards'
Hazards associated with volcanoes?
Dust emissions seed torrential rainfalls resulting in mud lahars
Flooding results from volcanic debris blocking rivers
Which eruptions have basaltic lava?
Which eruptions have rhylotic lava?
Which eruptions are andesitic?
Characteristics of Icelandic eruption?
Lava flows gently from fissures
Characteristics of Hawaiian eruption?
Lava flows gently from a central vent
Characteristics of a Strombolian eruption?
Frequents explosions of tephra and steam. Occasional, short lava flows
Characteristics of Vulcanian eruption?
Less frequent, but more violent eruptions of gases, ash and tephra
Characteristics of a vesuvian eruption?
Following long periods of inactivity, very violent has explosions blast ash high into the sky
Characteristics of peléean of eruptions?
Very violent eruptions of nuées ardentes
Characteristics of Plinian eruptions?
Exceptionally violent eruptions of gases, ash and pumice. Torrential rainstorms cause lahars.
Definition of a dormant volcano?
Has not erupted within historic times. More than 10,000 years is extinct
Montserrat warning signs?
July 1995- volcano began to erupt ash and dust.
Scientists began to monitor gases, microquakes and changes in the volcano shape.
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.
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
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.
Difference between focus and epicentre?
Focus is the breaking point of the earthquake.
Epicentre is the point on the surface directly above the focus.
What effects the nature of the hazard?
How large an area did it effect
What makes a population vulnerable?
Population - density
Type of population
Hazard proof buildings
Strategies to manage volcanoes?
Use of media
Outlets of steam and gas
Gas can be carbon dioxide and monoxide
Solfatara when sulphurous gas- Naples
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.
How many people are at risk from Etna?
Years when Etna erupted?
Sea floor spreading?
American geologist studied ages of rocks. Oldest rocks nearer to coast to USA and Caribbean.
Rate of 5cm a year
Features with Constructive margins?
New crust and basaltic rocks
Shallow focus earthquakes
Features with destructive?
Deep ocean trenches
Island arcs- two oceanic
Example of deep ocean trench?
Peru- Chile trench along the Pacific coast of South America
Pacific plate moves- 5-10cm a year
Pahoehoe and blocky aa lava common
What happens to Hawaii when moves away from hotspot?
Lava becomes more Alkali, cinder cones may appear
Steep sided cones associated with pyroclastic flows
Secondary effects of Haiti?
Strong aftershocks- 6.1
Inflation in food prices
Prison destroyed- lawless
Cholera kills- 1500
Immediate responses to Haiti?
International search teams- UN
US military distributed aid
16,000 UN troops to restore order
UN world food programme
Long term Haiti responses?
$11.5 billion reconstruction package
Life safe building codes- locals employed as builders
Difference in price of traditional and life safe buildings?
Cost 15% more
When did l'aquila occur?
Cause of Haiti?
Strike- slip fault
Carribean and North American plate
Factors of Haiti earthquake?
In late afternoon 16.53
Shallow focus- 13km
Epicentre- 24km from Port-au-prince
70% pop on less than $2 per day
Causes of l'Aquila?
African plate pushing north on Eurasian plate
Slip fault line underneath mountain range
Factors of L'Aquila earthquake?
Occurred at half 3 in the morning
Epicentre 7km from l'Aquila
Shallow focus- 10km
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
Responses of l'Aquila? I
Rescue efforts haulted by Aftershocks
People still in temporary accommodation 3 years later
Rebuilding programme- $16 billion
Countries effected by Boxing Day
Indonesia, Thailand and Sri Lanka
Deaths and missing after Boxing Day?
Cause of Boxing Day?
Indo- Audtrailian plate pushing north under Eurasian plate
Ocean floor pushed up several metres
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
Immediate responses of Boxing Day?
160 aid organisations
Australian Air Force
Long term responses to Boxing Day?
Tourist facilities prioritised
Education in schools and practice drills
Reconstruction- thousands homeless years later
Political barriers and tension
Background to Japan 2011?
9 magnitude earthquake
North American plate caused Pacific plate to slip upwards 10m
Japan's warning system gave minutes to escape
10waves, overwhelmed tsunami defence walls
Primary impacts? Japan 2011
Building collapsed or set ablaze- broken pipes
Flooded 500 square km
Skyscrapers shook not collapse
25,000 dead or missing
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
Intermediate responses of Japan 2011?
Helicopters from rooftops
No looting or violence reported
Exclusion zones set up
Survivors huddles in shelters