geography ✿ global hazards

extreme weather

weather that is unusual and can cause a threat to life

where is the Hadley cell located?

on the equator, between 30°-40° north to south

where is the ferrel cell located?

30°-60° latitude

where is the polar cell located?

60°-90°

how are low pressure belts formed?

what do they result in?

• warm air rises, creating lower surface pressure

• rising air cools and condenses, creating clouds and precipitation

• result in → wet, unstable weather, more precipitation and strong winds

how are high pressure belts formed?

what do they result in?

• cool air sinks, creating higher surface pressure

• air then warms up and dries out

• result in → dry, stable and little precipitation (desert and semi-arid zones)

What type of winds are usually associated with low pressure systems? [2]

high/ strong winds

Explain how the global circulation system causes extremes of rainfall in one part of the world. [2]

• in high pressure areas

• sinking air warms up, so less condensation occurs so no clouds are formed

Explain how the global circulation system causes extremely high temperatures in one part of the world. [2]

• in high pressure areas

• due to sinking air warming up, there are only a few clouds this means there is little clouds to block the sun

Identify the type of natural weather hazard shown in Fig. 1.

drought

explain one way in which global atmospheric circulation creates a climatic zone in the tropics

• there is sinking air at the Tropics

• which means there is no condensation

• so clouds can’t form, leading to dry conditions

explain one way in which global atmospheric circulation creates a climatic zone at the poles

• high pressure is formed at the poles as cold dry air sinks

• which produces stable conditions and little rain

explain one way in which global atmospheric circulation creates a climatic zone at the equator

• the equator is in between the two Hadley cells

• low pressure is created due to rising air warming and condensing, leading to cloud formation

Give two types of extreme weather associated with tropical storms

• heavy rain

• strong winds

describe how a tropical storm is formed

• tropical storms form over warm oceans over 27°c, which provides the energy

• water evaporates, making the air warm and rise, creating low surface pressure

• warm air condenses, creating strong clouds

• the earths spinning makes the storm start to spin

• a calm centre, the eye, is formed with the strong winds in the eye wall

El Niño

when trade winds are weakened/ reversed causes warm water near South America, leading to droughts in Australia

La Niña

when trade winds become stronger, causing warm water near Australia, causing droughts in South America

what are 3 effects of the droughts caused by La Niña and El Niño

• crop failures

• water shortages

• increased risk of wildfires

continental crust

crust found underneath large land masses

oceanic crust

crust found underneath the oceans. (ocean floor)

epicentre

the Earth's surface directly above the focus

focus

where the earthquake starts below the Earth's surface

how deep under the crust are shallow-focus EQs?

0-70km

how deep under the crust are intermediate EQs?

70-300km

how deep under the crust are deep-focus EQs?

greater than 300km

Describe what a hot spot is. [2]

an area of the earth’s crust where unusually high heat flow is linked to volcanic activity

constructive plates

• tectonic plates moving apart

• both volcanic eruptions and earthquakes can occur here (Mid-Atlantic Ridge)

destructive plates

• tectonic plates move towards one another.

• The oceanic crust is forced to sink, the continental crust rises above

Conservative plates

• tectonic plates move past each other

• only earthquakes occur here

Collison plates

• two plates move towards each other

• the crust is forced upwards forming fold mountains such as the Himalayas

Convection currents

Hot currents that make plates move

what are earthquakes caused by?

• EQs occur at all plate boundaries

• EQs happen when tectonic plates move, causing pressure and a sudden violent shake occurs

• they can also occur when humans drill or mine into the crust

Seismic waves

Shock waves from earthquakes

what does a Richter scale measure?

the magnitude of earthquakes

what are seismometers used to detect?

seismic waves from earthquakes

what does the Mercalli scale measure?

the damage caused by earthquakes (1-10)

Explain how the movement of tectonic plates at a destructive plate boundary causes volcanoes to form. [4]

• The tectonic plates move towards each other and one plate is forced to subduct

• this causes crust to melt due to friction

• pressure in magma chamber builds up

• molten material rises as it is dense

• magma moves through cracks of the crust

Volcanoes are formed on the margins ___________ and __________

Constructive and destructice

State 3 features about composite volcanoes

• found at destructive margins

• most violent eruptions

• lava is thick and heavy

state 3 features about shield volcanoes

• found at constructive margins

• Not as violent eruptions

• Lava is thin and runny

Name the process that causes the Earth’s tectonic plates to move. [1]

convection currents