Unit 1: Topic 2 - The Restless Earth

Question 1

Plate Tectonic Margins

Answer 1

There are 3 different plate margins:

• Constructive
• Destructive
• Conservative

CONSTRUCTIVE MARGINS:

e.g. North American Plate + Eurasian Plate

When two plates pull away from each other.

Constructive margins occur frequently under the ocean. By pulling tectonic plates away from each other, this causes magma to be pushed from the mantle. The magma then cools creating a MID-OCEAN RIDGE.

There are volcanoes involved in this plate margin and sometimes the volcanoes emerge above sea-level.

DESTRUCTIVE MARGINS

• —->
• —->

When plates slide past each other.

Neither plate is subducted. No collision, therefore no mountains or volcanoes. Build up of pressure may lead to earthquakes.

Sometimes the plates move in a similar direction but different speeds which leads to tearing of the crust.

Question 2

Fold mountains

Answer 2

Fold mountains were created 65 million years ago by destructive margins at COLLISION points. Newer fold mountain ranges are higher such as the Himalayas. Older ranges include the Cambrian mountains.

Where an area of sea separates 2 plates there are depressions called ‘GEOSYNCLINE’ contain sediments that lay at the sea floor. Gradually overtime the sediments are compacted into sedimentary rock.

Layers of sedimentary rock become crumpled and overtime it rises above sea levels as a range of fold mountains. Rocks that fold upwards are know as ANTICLINES.

Take the Alps for an example.

Question 3

Ocean Trenches

Answer 3

Ocean trenches are formed by DESTRUCTIVE margins. When a subduction of an oceanic plates occurs, a trench is formed. A trench is a natural depression of this process. The Mariana trench being the deepest trench in the world.

Ocean trenches are always asymmetrical.

Possible human use near ocean trenches are the continental shelves that are no deeper than 200 metres off the coast. This includes fishing and drilling oil.

Question 4

Shield Volcanoes and Composite Volcanoes

Answer 4

SHIELD VOLCANOES:

• Gentle slopes
• Wide base
• Runny lava
• Regular and frequent eruptions
• Lava pours out with little violence

CONSTRUCTIVE MARGIN

As the plates pull apart, magma rises upwards from the mantle to fill the gap. This adds new rock to the spreading plates and also gives it a wide base. Some volcanoes grow high enough to become volcanic islands.

One example would be ‘Nyiragongo’.

COMPOSITE VOLCANOES/STRATA VOLCANO:

• Tall cone with narrow base and steep sides
• Made of alternative layers of lava and ash
• Irregular with long dormant periods
• Violent explosions possible

DESTRUCTIVE MARGIN

When the oceanic plate is subducted, it melts and forms magma. The friction between the two plates and the pool of magma creates and pressure and tension to force the magma along a crack where it erupts at the surface to build up a volcano.

One example would be Mount St. Helens.

Question 5

Super Volcanoes

Answer 5

The distribution of super volcanoes are generally along plate margins, however there are a few exceptions; Yellowstone is located in the centre of the North American Plate and a few others are in the centre of plates.

Composite volcanoes are usually found along destructive margins, whereas some super volcanoes can be found in the centre of plates.

FORMATION OF SUPER VOLCANOES

1) Rising magma cannot escape and a large bulge appears on the surface.
2) Cracks appear on surface, as well as a large bulge.
3) Magma chamber collapses forming a depression called a CALDERA.

Super Volcanoes VS. Composite Volcanoes

• 100km wide - 10km wide
• 1000km3 of ash - 1km3 of ash

POTENTIAL EFFECTS OF SUPER VOLCANO

• Famine
• Volcanic winter - Ash will cover the world
• Pyroclastic flow (50-100km)
• Ash will fall up to 1000km
• Air traffic would stop

GEOTHERMAL FEATURES

• Geysers
• Hot springs
• National park
• Grand Canyon

Question 6

Earthquakes

Answer 6

Seismic waves are measured using a SEISMOMETER which produces a SEISIMOGRAPH.

FOCUS - Where an epicenter originates from.

EPICENTRE - The place directly above the focus

SEISMIC WAVES - Energy of an earthquake.

Seismic waves radiate out from the epicentre.

Most damage is closest to the epicentre although not always the case. An epicentre could originate where nobody lives.

The further you go from the epicentre, the weaker the energy of the waves.

P-WAVES

PRIMARY WAVES are the first to arrive. The waves moves forwards and backwards.

They can pass through liquids and solids.

This means the liquid outer core will not cast a shadow for P-Waves.

They can give vital seconds notice of the damaging waves which will follow - enough time to turn off gas and electricity and evacuate lifts.

S-WAVES

• Second waves to arrive.
• Side-to-side movement.
• Can only pass through SOLIDS.
• Liquid outer-core casts a shadow of those seismic waves.

L-WAVES

• Slowest and arrive last
• Move crust up and down
• Cause the most amounts of damage.
• They do not travel far as they lose energy quickly. Damage is concentrated close at epicentre.

Question 7

The Richter and Mercalli Scale

Answer 7

RICHTER SCALE

• Measures how powerful earthquakes are.
• Scale goes up in 10s i.e a LOGRITHMIC SCALE.
• Precise readings using a seismometer.

MERCALLI SCALE

• Gives an idea of what the damage is and does not require geography equipment.
• ## Scales go up in ROMAN NUMERALS.

Question 8

Protecting Against Earthquake Hazards (Specific to Japan)

• Responses + Management

Answer 8

PROBLEMS

1) Densely Populated
2) Tightly packed streets
3) Lots of electricity cables overhead
4)

MANAGEMENT

1) Modern buildings are ASEISMIC (life-safe and cause no damage to buildings).
- These buildings are flexible by using materials such as timber and walls are all made of rice paper.
- Windows are also shaped into triangular braces for further rigidity.
- Buildings have rubber shock-absorbents at the base of the building to absorb shock waves.
- Limit of 50 storeys to reduce collapsing.
- Steel frames sway
- Foundations sunken into bedrock, avoiding clay.
- Wide base of building for more stability.

2) Bridges are also ASEISMIC in the way that they have rubber shock-absorbents too.
3) People do not live on reclaimed land because it is susceptible to liquid-faction.
4) Roads are connected directly to buildings to provide quick exit.

RESPONSES

1) Britain sends rescue teams from abroad for international help.
- Use dogs to sniff out survivors
- Tokyo disaster response center coordinates rescue and fire teams.

2) Japanese drills are trained regularly