Restless Earth Flashcards
Constructive plate boundary
2 plates move apart due to convection currents in mantle
Magma rises through crust then cools and solidifies
Process repeats until new rock builds up forming volcano
Earthquakes included
E.g. Mid Atlantic Ridge
Destructive plate boundary
Denser oceanic plate is pushed under continental plate (subduction)
Friction where the plates slide melts mantle to become magma
Magma rises through gaps in continental plate
If it reaches surface it becomes a volcano
E.g. Nazca plate forced under South American plate
Earthquakes may happen
Conservative plate boundary
2 plates slide past/move in same direction at different speeds
Pressure builds along a fault
Friction causes earthquakes then the plates jerk free
E.g. San Andreas Fault, California
Collision plate boundary
2 plates of similar densities move together
Causes material between them to buckle and rise forming fold mountains
Earthquakes are common
E.g. Himalayas are fold mountains
Vent
Opening where lava flows from
Magma
Molten rock from deep within the earth
Lava
Molten magma when it erupts at the surface
Crater
The hollow at the mouth of volcano
Pyroclastic flow
Hot avalanche of gas, ash, cinders and rock that rushes down slopes of volcano after eruption
Lahar
Fast flowing mudflows made of water mixed with ash
Shield characteristics
Constructive plate Little violence Regular eruptions Basic lava (runny) Wide base, flat sides made of lava E.g. Hekla
Composite characteristics
Destructive plate Irregular eruptions Acid lava (viscous, thick) Narrow base, steep sides made of alternate layers (lava then ash and rocks) E.g. Mt St Helens
Advantages of living with volcano
Fertile soil with minerals (e.g. boxite) Hot springs Geothermal power Mud used for skin care Tourist attractions (e.g. Yellowstone National Park) Responsible for building new land
Disadvantages of living with a volcano
Destruction of vegetation, crops Loss of wildlife, homes Severe injury, death Living in fear Dangerous gases, avalanches Dormant volcanoes can erupt at any time Disease and fires
Use of aircraft…
Flying over volcano because they can measure gas given off by the volcano.
Seismometers…
Because these monitor earthquakes which increase as magma rises.
Tilt meters…
Used to detect swelling of volcano because as volcano fills with lava it can bulge.
Boreholes…
Measure water temperature because as magma rises it heats up the water.
Lithosphere
It’s made of the solid crust and upper mantle
Asthenosphere
The layer below the lithosphere where it’s less solid and convection happens
Oceanic crust
Under the ocean
Mostly made of igneous rock, which is very dense
Much thinner than the continental crust but it is much heavier
Continental crust
Forms land
Mostly made of granite, which has low density
Usually very thick, but lighter then oceanic crust
Outercore
The outercore is made of liquid, but also iron and nickel.
When the outercore moves around the innercore the Earth’s magnetism is created.
Innercore
The innercore is a solid ball made of nickel and iron (NiFe).
It’s the smallest and hottest layer.
The innercore is so hot that it melts all the metal ores in the outercore into liquid magma.
Why do the plates move?
In the mantle the radioactive decay drives the magma to circulate in huge convection currents.
The movement causes the crust to move.
What is Pangea?
A supercontinent from when all the continents were joined together
How do we know that the continents were connected?
Identical rocks and fossils dating back 250 million years have been found in west Africa and Southern America, which tells us that they were once connected.
What happened to Pangea?
Pangea started to split apart about 200 million years ago, and since then, plate tectonics have moved the continents to the position they’re in today.
What is a plate boundary?
Where 2 plates meet
How many individual sections of the Earth are there?
4
Crust, mantle, outercore, innercore
Focus
The point in the earth’s crust where the earthquake originates
Mercalli scale
A means of measuring an earthquake by describing and comparing the damage done
Epicentre
The point on the earth’s surface directly above the focus
Shock waves
Seismic waves generated by earthquakes
Richter scale
A scale which measures earthquakes based on scientific recordings of the amount of movement
Earthquake
A sudden and brief period of intense ground shaking
Preparing for a volcanic eruption:
- Emergency supply of basic provisions
- Emergency services to be ready to deal with the incident
- Be ready to evacuate residents with a clear evacuation route
- Creating an exclusion zone around the volcano with strict access
- Good communication system to alert locals
A damper
Reduces building sway
Cross bracing
Stops floors collapsing
Shock absorbers
Built into cross braces
A steel frame
Strong and also flexible, stops cracking
Double glazed windows
Strong, stops broken glass showering down
Very deep foundations
To prevent collapse
What is Mount St Helens?
MEDC
Mount St Helens is on the plate boundary between the Juan de Fuca plate and North American plate.
When it erupted in 1980 it permanently changed the surrounding landscape.
Primary effects of the Mt St Helens eruption:
- Pyroclastic flow destroyed forests and logging camps
- 63 people were killed, mainly by poisonous gases
- Lahars covered an extensive area surrounding the volcano
Secondary effects of the Mt St Helens eruption:
- Ash blocked rivers destroying popular fishing sites and causing flooding. This in turn destroyed crops and livestock
- Flooding destroyed communications such as road and railway bridges
Short-term responses and results:
Mt St Helens
- Communications such as roads and bridges were repaired
- People were rehoused
Long-term responses and results:
Mt St Helens
- Soil fertility improved due to the ash deposits
- The volcano is now more carefully monitored
- Tourism has increased, boosting the local economy
Short-term aid :
Mt St Helens
- The National Guard and State Troopers rescued stranded people
- Provided shelter for those who lost their homes
- Gave medical supplies to those who were injured
- The aid operation rescued 198 people
Long-term aid:
Mt St Helens
- A million tonnes of ash were removed from roads, buildings and airports
- Millions of trees were replanted as there was a huge loss of timber which would cost $300 million
- Compensation was given to farmers because the produce on their farms were destroyed by being covered in ash
What is Montserrat?
LEDC
A small island in the Caribbean Sea between North America and South America. It has been dormant for 300 years before 1995, when it began to give of warning signs of an eruption. Once Chances Peak had woken up it remained active for 5 years.
Short-term results and responses:
Montserrat
- Evacuation
- Abandonment of the capital city
- The British government gave money for compensation and redevelopment
- Unemployment rose due to the collapse of the tourist industry.
Long-term results and responses:
Montserrat
- An exclusion zone was set up in the volcanic region
- A volcanic observatory was built to monitor the volcano
- New roads and a new airport were built
- Services in the north of the island were expanded.
- The presence of the volcano resulted in a growth in tourism
