Geography: Chapter 2 - Tectonic Hazards

Such as earthquakes or tsunamis which involve the movement of tectonic plates in the earths crust

Crust, asthenosphere, mantle, outer core, inner core

The Earths internal structure is divided into layers

It’s extremely hot and under a lot of pressure

The inner core is solid

The outer core is liquid

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

It’s very thin compared to the thickness of the mantle and core

Continental crust and oceanic 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

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

They can be tracked from space using GPS

Where 2 plates meet

They describe the different ways the plates are moving

There constructive, destructive and conservative plate margins

The interaction between the different tectonic plates and the mantle beneath leads to triggering of earthquakes and volcanic activity

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

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

Found at all three types of plate margins

Found in land and sea

Only at constructive and destructive plate margins

Found in both land and sea

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

The margins occur when tectonic plates move apart from each other - most move a few cm a year

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

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

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

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

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

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

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

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

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

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

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

It was recorded in chile and was 9.5 on Richter scale in 1960

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

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

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

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

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

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

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

Helps the authorities, emergency services and individuals to act quickly and calmly so there is less chaos and fewer injuries and deaths

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

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

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

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

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