The Earth’s Plates
Categorising Volcanoes
Magma Chamber
Main Vent
Secondary Vent
Volcanoes are formed when semi-molten rock called magma rises and forces its way through weaknesses in the crust and then as surface pressure builds up there is a volcanic eruption. When magma reaches the surface of the earth it turns into lava.
An active volcano is likely to erupt soon. An extinct volcano is considered unlikely to erupt. A dormant volcano isn’t currently active but has erupted within the last 1000yrs and may erupt again.
Cone volcanoes tend to be found at destructive plate boundaries and they are tall with steep sides.
This is because they give out thick and viscous acid lava which flows slowly and hardens quickly.
They erupt violently throwing out steam, gas and lava bombs.
Shield Volcanoes are generally found at constructive plate boundaries and they are low with gentle slopes.
This is because they are formed by the thin and runny basic lava.
These volcanoes erupt quite frequently and gently.
Some volcanoes are made up of layers of lava and ash that alternate and these are known as composite volcanoes.
When they erupt they throw a lot of ash into the air because of their ash layers.
How are Earthquakes Caused?
Plates do not move smoothly so when a plate gets stuck, pressure builds up. When the pressure is released an earthquake can take place. The point where the pressure is released is known as the focus and the point directly above it on the surface of the earth is called the epicentre.
Seismic Waves are the shock waves created by the earthquake and they lose energy the further they travel from the focus and epicentre. They create the greatest damage at the epicentre and sometimes they can even lead to tsunamis.
Case Study: Kashmir
Date: 8/10/2005
Time: 08:52 (Pakistan standard time)
Location:
- Indian controlled Kashmir
-
19km northeast from Muzaffarabad.
- North of Pakistan.
- Northwest of India
- Continent of Asia
What:
- Moment Magnitude Scale: 7.6
- Richter Scale: 5.2
- Death toll: 74,698
- Landslides
Why:
- Eurasian and Indian plate boundary
- Also caused Himalayas formation
- Destructive plate boundary
Who:
-
73,338 (Northwest Frontier Province)
- 1,360 (Indian Administered Kashmir)
- 4 (Afghanistan)
- 106,000 were injured
- 3 million left homeless
Case Study: L’Aquila
Date: 6/04/2009
Time: 03.30
Location:
- L’Aquila, Italy
- Europe
- 100miles northeast of Rome
What:
- Third biggest earthquake in the region
- Richter Scale: 6.3
- Death toll: 300
- 15,000 buildings off limits
Why:
- On Eurasian and African tectonic plate boundaries
- Destructive plate boundary
Who:
- 50,000 homeless
- 26 council districts hit - in 35km radius
- 150 killed
Management Strategies
Himalayas
Apennines
297 (low)
15,000 – Including historic buildings
50,000 (medium)
3.3m (very high/ devastating)
Very little
Adequate amount
- Government compensation
- Homeless
- Buildings Destroyed
- Deaths
- Villages wiped off map
- Many injured
- Many trapped
- Mountain villages cut off
- Orphans
- Media coverage
Comparing the effects of the two earthquakesL’Aquila
Kashmir
600,000 homes – Also roads and bridges
87,351 (very high)
Magnitude: 6.3
(Richter scale)
106,000
Magnitude: 7.6
(Richter scale)
Why do effects of Earthquakes vary?
- Magnitude: Kashmir’s Earthquake was over 10 times stronger
-
Population Density: L’Aquila = 59/km2 Kashmir = 200/km2
- Rock/Soil type
- Wealth: Kashmir is in an LEDC (Pakistan) but L’Aquila is in an MEDC (Italy)
Case Study: Montserrat Volcano
Management:
- Evacuation to a safe zone
- Evacuation to Antigua, USA and UK
- Mapping pyroclastic flows as warning
- Aid from UK and USA
Why hasn’t it recovered?
- Lack of money to rebuild and clean
- Volcano continues to erupt
- Less people to help rebuild
- Lack of education to rebuild
- Lack of resources and equipment
Why do people live near volcanoes?
- Less expensive due to lower demand
- Unaware of danger - lack of education
- Dormant volcano
- Fertile soil
- Employment in tourism/(research)
When?
-
June 95: 1st eruption (350yrs dormant)
- June 97: huge eruption and pyroclastic flow (hot ash and lava)
Why?
Destructive boundary: Caribbean/S. American
Where?
In the Caribbean Sea east-southeast of Puerto Rico and north of Venezuela.
GENERAL
