Unit 2 - The natural environment Flashcards
Structure of the earth
- Crust - 100km thick - oceanic & continental crust
- upper mantle - 400km deep 100-1300˚C
- Lower mantle - 700km deep 200-2500˚C
- Outer core - 2900km deep 2500-3000˚C
- Inner core - 5150km deep 4000-5000˚C
Oceanic crust
Thin but very dense
Continental crust
Thick but less dense
4 types of plate boundaries
- Divergent
- Convergent
- Collision
- Transform
Divergent plate boundary
- Two plates move apart
- Magma rises and fills gap - erupts as Laval and solidifies to make new crust
- Also known as a constructive boundary
- Example: Mid-Atlantic ridge - North American and Eurasian plate
Convergent plate boundary
- Plates move towards each other
- When continental and oceanic plates come together - denser oceanic sinks and continental rises - forms subduction zone
- Friction between plates and the mantle melts oceanic crust
- Magma rises and erupts as a volcano
- Also known as a destructive boundary
- volcanoes and earthquakes occur
- Example: Nazca plate subjects under South American plate
Collision plate boundary
- When two continental plates of similar densities move towards each other
- Crust pushed up and forms fold mountains
- Only earthquakes occur
- Example: Himalayas growing with Indian & Eurasian plate
Transform plate boundary
- Plates move pas each other in opposite directions or in same direction at different speeds
- Also known as a conservative boundary
- Volcanoes and earthquakes occur
- Example: San Andreas Fault - USA
Convection currents in the mantle
Hotter less dense material due to outer core rises and colder denser material sinks
Cause of earthquakes
- Convection currents cause movement of plates
- Plates can get stuck and build up pressure
- When pressure is too high the boundary suddenly moves
- All stored energy is released in seismic waves
- Waves move through the crust and cause shaking
Focus
The point underground where the release of seismic energy happens
Epicentre
The point above the focus on the surface of the crust
Scales of earthquake magnitude
- Richter scale - energy released
- Moment magnitude scale - distance the fault line has moves
- Mercalli scale - visible damage
Causes of volcanoes
- Formed when ruptures on the crust allow lava, volcanic ash and hot gases to erupt
Features of volcanoes
- Magma chamber
- Layers of ash and lava
- vent
- Crater
- Lava flow
- Ash cloud
Places where volcanoes occur
- Divergent plate boundaries
- Convergent plate boundaries
- Hot-spots - areas of super-heated plumes of magma under the crust
Active volcano
Erupts regularly
Dormant volcano
Potential to become active, gap of eruptions from less than a year to over 10000
Extinct volcano
No activity detected in human history - will not erupt again
4 types of Volcanoes
- Stratovolcano/composite
- Shield volcano
- Cinder cone
- Fissure vent
Stratovolcano/composite
- Forms at convergent boundaries
- Erupts violently and unpredictably
- Lava is thick and slow moving
- Steep sides and classic cone shape
Shield volcanoes
- Forms at divergent boundaries and hot-spots
- Eruptions are less explosive and more predictable
- Lava is runny and flows for long distances
- Gently sloping sides
Cinder cone
- Hot lava and ash blasts into the air
- Substances cool, fall and stick to the cone’s slope as opposed to flowing
Fissure vent
- Linear volcanic vent where lava erupts
- Often few meters wide and kilometers long
Factors that increase risk and vulnerability
- Urbanization - densely populated areas with less robust buildings increases vulnerability
- Economic development - LEDCs have poorer infrastructure, planning, preparation, healthcare, systems and emergency responses
Primary effects
Direct result of earthquakes or eruption
Secondary effects
As a result of primary effects
Primary effects of volcanic eruptions
- Deaths and injuries
- Crop damage
- Roads and infrastructure damage
Secondary effects of volcanic eruptions
- Spread of disease
- Homelessness
- Shortage of resources
- Loss of jobs and businesses
- Transport difficulties
- Tsunamis
- Mudflow
- Fires
Primary effects of earthquakes
- Deaths and injuries
- Road and infrastructure damage
Secondary effects of earthquakes
- Spread of disease
- Homelessness
- Shortage of resources
- Loss of jobs and businesses
- Tsunami
- Landslides
- Fires
Causes of volcano effects
- Pyroclastic flow
- Lava flow
- Tephra
- Volcanic bombs
- Toxic gas cloud
Causes of earthquake effects
- Collapse of buildings
- Falling objects
Reducing risk of earthquakes
- Earthquake resistant buildings
- Education - drills, practice and planning
- Hazard mapping - identify areas of high risk
Features of earthquake resistant buildings
- Reinforced elevator shaft
- Automatic shutters to prevent glass falling
- Fire-resistant materials
- Deep foundations
- Rubber shock absorbers in foundation
- Flexible joints for building to move
- Interlocking steel frame
- Counterweights on roof for vibrations
Predicting volcanoes
- Seismometers - detect tremors in ground before eruption
- Tiltometer - detect changes in angle of slope - magma chamber grows
- Gases - gases released in increasing quantities before eruption e.g. CO2
- Satellite observation - hot areas detected under earth’s surface
- Helicopter observation - aerial perspective can show danger under the surface
- Volcano’s history - frequency and violence of previous eruptions
- Volcanologist - people skilled at predicting volcanoes
Pyroclastic flow
Mixture of ash, pumice and hot gases that flows down a volcano
Lahar
Fast deadly mudslide made of water, mud and volcanic debris
Opportunities of volcanoes
- Fertile soil - high in magnesium and potassium
- Popular attraction - good for tourism industry
- Rare metals - gold, copper, zinc, silver, rubies and diamonds
- Geothermal energy - heat from rising magma
