Restless Earth Flashcards
What happens at a destructive plate boundary
Oceanic crust subducts under the continental crust.
What happens at a constructive plate boundary
Two oceanic plates push against each other then move upwards forcing magma between them.
What happens at a conservative plate boundary
Plates move slowly past each other, one is moving faster than the other, they get stuck and friction and pressure builds up along the fault line, when the pressure is released it causes an earthquake.
What happens at a collision plate boundary
Two continental plates collide, neither plate is forced under the other, both plates are forced up and form fold mountains.
Distribution of fold mountains
Distributed in a linear pattern along convergent plate, for example the Andes along the west coast of South America where the Nazca and South American plates collided.
Formation of fold mountains
1) Tethys sea between Indo-Australian and Eurasian plate
2) The two plates move towards each other and collide forcing the sediment at the bottom of the Tethys Sea to compress and form fold mountains.
Problems people face in fold mountain areas - Alps
- Earthquakes
- Tourism - negative environmental impacts
- Avalanches - settlements located in the bottom of the valley
- Poor access - steep rocky terrain
- Expensive to transport food
- Flooding
- Challenging climates cold winters/warm summers
- Global warming - effects cold environments, glaciers retreating, knock-on effect to people who’s businesses require a cold climate
Uses of fold mountains - Alps
~Farming
pastoral/live stock e.g. Cattle - limited to valley bottoms in winter and higher pastures during summer, called transhumance. Lush grass makes better quality dairy products e.g. Milk, cheese and chocolate.
~Tourism
Winter sports - Chamonix
Summer walking - Haute Route 180km Chamonix to Zermatt.
~Hydroelectric Power
Grade Dixence dam in Switzerland, construction began in 1953 and opened in 1964. It’s 285m tall which makes it the highest gravity dam in the world. Area of 3.65 kilometres squared. On the Dixence river, the reservoir holds 400 000 000 metres squared of water. Powers 400 000 homes.
~Forestry
Predominantly on south facing slopes because they receive more sunlight, renewable.
Earthquake key words
Focus - The point in the Earth’s crust where the earthquake originates
Earthquake - Is the shaking and vibration of the Earth’s crust due to the movement of the Earth’s plates.
Epicentre - The point at the Earth’s surface directly above the focus.
Seismic Waves - Waves generated by an earthquake that pass through the Earth’s crust.
The Richter Scale
Logarithmic scale which means that each number increases by a factor of 10 e.g. 2 is 10 times bigger than a 1. A seismograph is used to detect the amount of ground movement, this is interpreted on the Richter Scale to illustrate the earthquakes magnitude. 1 on the Richter scale can only be detected by a seismograph and 9 and over is near total devastation.
Mercalli Scale
The Mercalli Scale is used to measure the earthquakes intensity. Used in Roman Numerals so ranges from I which is not felt and XII which is almost complete destruction. The scale gives a value to the impacts or effects of an earthquake on the Earth’s surface, humans, objects of nature and man-made structures.
Primary and secondary effects of earthquakes
Primary Effects
- Collapsing buildings
- People killed e.g. by being trapped in homes, places of work and cars
- People injured e.g. by falling building materials
Secondary effects
- Fires, caused by earthquakes breaking gas pipes and bringing down electricity wires.
- Tsunamis, caused by an earthquake on the sea floor
- Landslides, most likely on steep slopes and in areas of weak rock e.g. sand and clays
- Diseases, such as cholera and typhoid spread easily when burst pipes lead to shortages of clean water and to contamination of sewage
Factors controlling the effects of an earthquake
Physical (what we can’t control)
- Magnitude on Richter Scale
- Depth of focus, shallow focus is more destructive
- Rock type, sand and clay vibrate more compared to hard surfaces
Human (what we can control)
- Density of population
- Building quality, self-built is more likely to be damaged than earthquake proof buildings
- Emergency procedures, lack of procedures compared to regular earthquake drills
New Zealand Earthquake - MEDC Case Study
- 4th September 2010
- Occurred at night time
- 7.0 on the Richter Scale
- Tremor lasted 40 seconds
- Epicentre about 55km from city of Christchurch
Effects - New Zealand earthquake
- No deaths reported
- Some serious injuries
- 100 000 homes damaged
- 500 buildings to be demolished
- Chimneys and walls fell from older buildings
- Roads blocked
- Traffic lights out
- Power, gas and water supplies disrupted
- Damage estimated at £1.8bn
Responses - New Zealand earthquake
- Evacuation of buildings
- Emergency services set to work
- Exclusion zones set up and enforced by the police and military
- Airport closed to check for damage
Were they prepared? - New Zealand earthquake
- Strict buildings codes exist
- Programme of upgrading buildings so they are earthquake-proof started in the 1970s
- Emergency services prepared and limited damage meant services such as hospitals stayed open
- Frequent earthquakes mean the city was well-prepared
- Wealthy country
Haiti Earthquake - MEDC Case Study
- 12th January 2010
- Occurred in the afternoon
- 7.0 on the Richter Scale
- Tremor lasted 1 minute
- Epicentre 25km from the capital Port-Au-Prince
Effects - Haiti
- Over 222 000 deaths
- Over 300 000 injuries
- 1.1 million displaced from their homes (over 90 000 homes destroyed)
- Many roads and bridges destroyed
- Telephone lines and electrical systems destroyed
- Schools and hospitals collapsed
- Fires
- Diseases spread due to poor living conditions and lack of sanitation
- Small, local tsunami
Responses - Haiti
- International aid teams distributed food, water and medical supplies
- 23 000 tents distributed and temporary camps set up
- People dug for survivors with their hands and basic tools
- People grieved for loved ones
- Large ares needed to be rebuilt
- Attempts to forbid new buildings in high-risk areas
Were they prepared? - Haiti
- No strict building codes
- Earthquake-proof buildings were limited
- Last major earthquake in Port-Au-Prince was in the mid-1700s-people had forgotten about the risk
- Poorest country in the Western Hemisphere - more than two thirds of the population live on less than £1.50 a day
- Many people are subsistence farmers
Volcanoes
A volcano is a cone-shaped mountain formed by surface eruptions from a magma chamber inside the Earth. When magma reaches the surface it is called lava. Volcanoes form from where magma escapes through a vent, which is a fracture or crack in the Earth’s crust. Lava and other products are thrown out of the crater. Every time an eruption occurs a new layer of lava is added to the surface of the volcano.
Key terms
Lahars - They’re a secondary product, mudflows formed by water picks up volcanic ash and deposits it as mud.
Pyroclastic Flows - Materials that move down the side of the volcano made up of rocky debris and gases with a speed of 450mph and a temperature of 1000 degrees.
Shield Volcanoes
Constructive plate boundaries. Plates move apart and magma rises to fill the gap which adds new rock to spreading plates, some magma may be forced to the surface through a vent. Some become big enough to from islands such as Iceland.
Lava type - Basic, low silica content, non viscous
Slope angle - gentle, flat, under 10 degrees
Composition - just lava
Eruptions are frequent and gentle, non volatile, violent and viscous
Examples are Surtsey, Iceland and Mauna Loa, Hawaii
