Chapter 2 - Tectonic Hazards Flashcards
What’s a tectonic hazard
Such as earthquakes or tsunamis which involve the movement of tectonic plates in the earths crust
Tell me the order of the earths internal surface starting from the surface
Crust, asthenosphere, mantle, outer core, inner core
The Earths internal structure is divided into layers
Tell me about the core
It’s extremely hot and under a lot of pressure
The inner core is solid
The outer core is liquid
Tell me about the mantle
It surrounds the core and is made of solid material that can flow very slowly, the upper portion of the mantle is weak
- the ASTHENOSPHERE - which can deform like plastic
Tell me about the crust
It’s very thin compared to the thickness of the mantle and core
Tell me the 2 types of crust
Continental crust and oceanic crust
Compare the 2 types of crust
They differ in chemical composition, thickness and density
Oceanic crust is thinner but denser than continental
Oceanic is younger and can be recycled at destructive plate margins whereas continental is not destroyed
What’s the lithosphere
The crust and upper mantle are chemically different but together form a rigid shell as the surface of the earth
It’s broken into several major fragments which move very slowly over the upper mantle
How can the movement of plates be tracked
They can be tracked from space using GPS
What’s a plate Margin
Where 2 plates meet
What are the 3 types of plate margin and what do they mean
They describe the different ways the plates are moving
There constructive, destructive and conservative plate margins
How do the tectonic plates lead to earthquakes
The interaction between the different tectonic plates and the mantle beneath leads to triggering of earthquakes and volcanic activity
What’s convection
A THEORy of how plates move
The cores temperature is around 6000 C - this caused magma to rise to the mantle and sink towards the core when it cools
The currents flow beneath the lithosphere - building up lateral pressure and carrying the plates with them
However only limited evidence has been found so far of convection currents
What’s ridge push and slab pull
Another theory for the movement of plates
At constructive margins- ocean ridges form high about the ocean floor and below the mantle melts - the molten magma rises as the plates pull apart and cool down to form new plague material
As the lithosphere cools, it becomes denser and starts to slide down away from the ridge which causes plages to move away from eachother - this is ridge push
At destructive margins the denser plate sinks back into the Mantle Under the influence of gravity which pulls the rest of the plate along behind it - this is slab pull
Where are earthquakes found
Found at all three types of plate margins
Found in land and sea
Where are volcanoes found
Only at constructive and destructive plate margins
Found in both land and sea
What are hot spots
Some earthquakes and volcanos occur in the middle of plates and these are known as hoy spots
It’s where the crust is through to be particularly thin
How do plates move at constructive margins
The margins occur when tectonic plates move apart from each other - most move a few cm a year
Tell me the way the plates move and why earthquakes are found on constructive plate margins
The upper part of the mantle melts and hot magma rises
As the tectonic plates are moved away from each other by slab pull, ridge push or a combination. The molten magma rises in between and cools down to form solid rock - this forms part of an oceanic plate, the new solid plate sometimes fractures as it is moved- causing earthquakes, usually small and not violent
How are volcanos formed on constructive plate margins
Volcanoes form as much of the magma never reaches the surface but it’s buoyant enough to push up the crust as the margins to form ridge and rift features
In a few places the magma erupts on to the surface producing a lava that is funny and spreads out before solidifying - over many eruptions a volcano that has typically a wide base and gentle slopes known as a shield volcano is formed
What forms when constructive plate margins move on land
A Rift Valley, where the land drops as the plates move apart
The strain put on the land as the tectonic plates move away from each other is splitting countries such as Iceland in two and causes cracks of faults to form on either side. So for example 100s of small earthquakes occur on Iceland on a weekly basis
How do plates move at destructive margins
Occur when tectonic plates move towards each other and collide. The effect this has depends on what kinds of plates are colliding
If 2 continental plates collide, they are both buoyant and so cannot sink into the mantle. As a result, compression forces the plates to collide and form and mountains
If an oceanic plate and continental plate move towards each other, the denser oceanic plate is subducted and sinks under the continental plate and into the earths mantle where it’s recycled, earthquakes, fold mountains and volcanoes occur
Why are earthquakes found at destructive plate margins
The pressure and strain of an oceanic and continental plate moving towards each other can cause the earths crust to crumple and form fold mountains, as the plates converge, pressure builds up and the rocks eventually fracture causing an earthquake
Why are volcanoes found at destructive plate margins
As the oceanic plate sinks deeper into the mantle, it causes part of the mantle to mantle. Hot magma rises up through the overlying mantle and lithosphere, and some can eventually erupt out at the surface producing a linear belt of volcanoes. The magma becomes increasingly viscous as it rises to the surface. Producing composite volcanoes which are steep sided and have violent eruptions
When does a deep ocean trench form
At a destructive plate margin, The oceanic plate as the denser of the 2 plates is subducted or pulled down into the mantle beneath the lighter and thicker continental plate under gravity. At the surface this creates a deep ocean trench
Tell me about Japan’s earthquakes/ volcanoes
It’s prone to earthquakes and volcanic eruptions, it’s has 118 active volcanoes
There are so many Becuase Japan lies on the margin of four plates
Many parts of Japan also experience earthquakes due to pressure built up in the plates as they move at this destructive plate margin
How do plates move at conservative margins
Occur when tectonic plates move parallel to each other, the 2 plates can move side by side- either in the same direction but at different speeds or simply in the opposite direction to one another
Why are earthquakes found at conservative plate margins
One theory is that pressure builds up at the margin of the tectonic plates as they are pulled along behind a plate being subducted elsewhere
As the plates move past eachother, friction causes them to become stuck
Pressure builds up and up until the rock fractures in an earthquake
Why are volcanoes not formed at conservative plate margins
As magma can’t rise to fill a gap as there is no gap created between the tectonic plates and therefore no new land is formed or destroyed Becuase there is no tectonic plate subducted into the mantle
What was the largest earthquake ever
It was recorded in chile and was 9.5 on Richter scale in 1960
What’s geothermal energy
In volcanically active areas, it’s a major source of electrical power - steam is heated by hot magma in permeable magma, then boreholes are drilled into the Rock to harness the super heated steam to turn turbines at power stations - it’s renewable
So people live in hazardous areas as they produce geothermal energy
Why do people live in hazardous areas for farming
Lava and ash eruptions can kill livestock and destroy crops and vegetation, after thousands of years weathering of this lava releases minerals and leaves extremely fertile soil rich in nutrients, land can be farmed to provide food and income
Why do people live in hazardous areas for mining
Not just dormant and extinct volcanoes that are mines but active ones too
It’s very dangerous:
Miners can afford little protective clothing
In last 40 years, 74 miners have died from fumes in volcanoes
Sulphur is produced and sold sometimes 100kg are carried up and down the rocky and slippery mountain paths
Miners can earn an average of $6 a day more than a coffee plantation so miners continue to live and work in dangerous areas
Why do people live in hazardous areas for tourism
Tourists visit volcanoes for the views, hot springs and adventure
More than 100 million people visit volcanic sites every year
The revenue they generate benefits that locals and the countries they are in
Why do people live in hazardous areas for family, friends and feelings
People don’t want to leave because friends and family are there
Often cheaper and easier to step - especially when risks may not be Perceived as dangerous enough
Or residents are in denial a disaster may occur
How do seismologists try to predict earthquakes
Use radon detection devices to measure radon gas in the soil and groundwater, which escapes from cracks in the earths surface
Sensitive seismometers are used to measure tremors or foreshocks before the main earthquake
How else can earthquakes be monitored and predicted
The locations and times are mapped to spot patterns and predict when the next earthquake will occur
Smartphones have GPS receivers and accelerators built in and can detect movements in the ground, which are analysed to potentially warn others further away
Animals are believed to act strangely when an earthquake is impending
How can planning for an earthquake help
Helps the authorities, emergency services and individuals to act quickly and calmly so there is less chaos and fewer injuries and deaths
How can you plan for an earthquake
Furniture and objects can be fastened down so they are secure from toppling over
Residents can learn how to turn off the main gas, electricity and water supplies to Their properties
Prepare emergency aid supplies,
- eg the American Red Cross provided safety checklists to help people prepare
How can you protect buildings from earthquakes
Designing buildings and strengthening roads and bridges to withstand earthquakes provides protection - called mitigation eg having automatic shutters that come down over Windows
However, very expensive so usually not possible to adapt existing buildings and though it may save live in an earthquake, after is may still need to be repaired and even rebuilt
How can monitoring and prediction reduce the risk of volcanic eruptions
Using satellites and tilt meters to Monitor ground deformation (changes in of the volcanos surface)
Seismometers measure small earthquakes and tremors
Thermal heat sensors detect changes in the temperature of the volcanos surface
Gas trapping bottles and satellites measure radon and sulphur gases released
Scientists measure the temperature of water in steams and rivers to see if it has increased
How can you protect buildings from volcanic eruptions
Very difficult to design a building from lava flows, Lahars, or weight of Debris and ash falling on roofs
Therefore, people need to evacuate their home to a safe location under the instruction of the authorities
How can planning reduce the risk of volcanic eruptions
An evacuation plan is one of the most effective methods of protections
Authorities and emergency services need to prepare emergency shelter, food supplies and form evacuation strategies
Exclusion zones can be designated where no one is allowed to enter where people are considered vulnerable and in danger
Residents can be educated on preventing loss of life, if residents not evacuated, they are taught to seek shelter or go indoors to avoid the dangers of falling ash and rock
