Geography: Natural Hazards
- Created by: 12RoMistry
- Created on: 21-06-21 20:20
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- Year 9: Geography Revision
- Natural Hazards
- Rivers and Flooding
- Factors affecting flooding
- Physical causes
- Heavy rainfall
- Long periods of rain
- Snowmelt
- Steep slopes
- Impermeable rock
- Very wet, saturated soil
- Compacted or dry soil.
- Human causes
- Urbanisation - more impermeable surfaces
- Deforestation - decreases interception and increases run-off
- Physical causes
- Flooding occurs when a river reaches its channel capacity.
- Hydrographs
- A storm hydrograph is a graph to show how and when a rainfall event affects the discharge of a river.
- Key parts
- Peak rainfall - top of tallest bar
- Peak discharge - top of curved line
- Lag time - time between peak rainfall and peak discharge
- Case study: Bangladesh
- Causes of flooding in Bangladesh
- Cyclones cause coastal flooding
- Lots of low-lying land
- Melt water from the Himalayas
- Heavy monsoon rains
- Increasing urban areas
- Responses to flooding
- Short term
- Flood air from gov. & other countries
- Water purification tablets
- People repaired embankments & helped rescue people
- Free seed given to farmers
- Long term
- Building embankments
- Building raised food shelters
- Introducing flood warning systems
- Emergency planning
- Dams planned
- Reducing deforestation
- Short term
- Causes of flooding in Bangladesh
- Factors affecting flooding
- Tectonics
- The Earth has four main layers
- The inner core
- 5,500 degrees Celsius
- Extremely hot
- Very dense solid
- Made from iron and nickel
- 5,500 degrees Celsius
- Outer core
- 2,000 km thick
- Liquid
- Mantle
- Semi-molten
- 3,000 km thick
- Crust
- Rocky outer layer
- 5 - 70km thin
- The inner core
- Movements in the Earth's crust
- Convection currents
- A movement within the Earth's mantle, caused by the heat of the core.
- Slab pull
- Older, denser tectonic plates sink into the mantle, pulling newer and less dense sections of plate along behind
- Plate boundaries
- Region of intense seismic activity, where tectonic plates meet
- Destructive/ Convergent
- Oceanic plate forced under lighter continental plate
- Friction causes melting of oceanic plate and may trigger earthquakes
- Magma rises up through cracks and erupts onto the surface.
- Friction causes melting of oceanic plate and may trigger earthquakes
- Example: Nazca plate in SA
- Oceanic plate forced under lighter continental plate
- Collision zones
- when two continental plates collide
- so both are forced up and form fold mountains.
- when two continental plates collide
- Constructive/ divergent
- when plates move apart
- Conservative
- Plates slide past each other in opposite directions, or in the same direction but at different speeds
- Friction is eventually overcome and the plates slip past in a sudden movemen
- shockwaves created produce earthquake
- Friction is eventually overcome and the plates slip past in a sudden movemen
- Plates slide past each other in opposite directions, or in the same direction but at different speeds
- Destructive/ Convergent
- Region of intense seismic activity, where tectonic plates meet
- Convection currents
- Continental Drift
- Theory that continental landmasses were drifting across the earth
- Alfred Wegener
- Theory that continental landmasses were drifting across the earth
- The Earth has four main layers
- Untitled
- Volcanoes
- opening in the Earth's crust
- It allows hot magma, ash and gases to escape from below the surface
- Parts of a volcano
- Magma chamber - large underground pool of magma
- Lava - magma, once it reaches the surface
- Crater - bowl-shaped basin in the top of the volcano
- Vent - central tube which magma travels through
- Ash, steam and gas - material thrown out by the volcano
- Volcanic bombs - larger material thrown out by the force of eruption
- Types of volcano
- Composite volcanoes
- steep-sided
- cone-shaped
- made up of layers of ash and lava
- sticky lava which doesn't flow very far.
- Example: Mt Etna
- Shield volcanoes
- gently sloping sides
- runny lava
- covers a wide area
- Gases escape very easily
- Example: Mauna Loa in Hawaii
- Composite volcanoes
- Active volcanoes
- Erupted recently
- Dormant volcanoes
- Erupted in the last 2,000 years
- Untitled
- Extinct volcanoes
- Not erupted for many thousands of years.
- Parts of a volcano
- It allows hot magma, ash and gases to escape from below the surface
- opening in the Earth's crust
- Rivers and Flooding
- Natural Hazards
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