Tectonic Hazards Flashcards
What is a natural hazard?
A natural event that has social impacts / A natural event that overlaps with human activities
What is a hazard risk?
The chance of being affected by natural events
What are four different types of hazards?
Volcanic eruption: Hot material such as lava is thrown out from a volcano
Earthquakes: When the ground shakes
Tsunami/Hurricane/Cyclone: A huge wave caused by an earthquake/volcanic eruption under the ocean
Landslides: Collapse of the earth from mountains or cliffs
Floods: When the water overflows from a river
What are the three main groups of natural hazards?
Geological hazards: hazards caused by processes e.g volcanoes, earthquakes, landslides
Hydrological hazards: hazards caused by the movement of water on land e.g flooding
Atmospheric hazards: hazards caused by the weather e.g. tropical storms, droughts tornadoes
What factors affect risk?
Urbanisation - Cities are densely populated areas so when an earthquake occurs more people are at risk
Climate change - Global warming leads to oceans becoming warmer. This will increase the number and intensity of tropical. (Ice caps lead to rising sea levels, increasing the risk of flooding)
Farming - When a river floods it leaves behind fertile silt which is good quality soil for growing crops. Therefore farmers will choose to put themselves at risk and live on floodplains so they can grow crops for food and income.
Poverty - People don’t have enough money to move so have no choice but to live in hazardous areas with poor construction e.g. landslides
What is an earthquake?
Earthquakes are vibrations in the Earth’s crust that create shaking at the surface. They are highly unpredictable and often occur suddenly without warning, mainly on the plate margins
Describe the structure of the earth
Crust - the outermost layer of the Earth, broken into tectonic plates.
Mantle - semi-molten part of the Earth.
Outer core - liquid iron and nickel
Inner core - solid iron and nickel
What is the earth’s crust broken into?
Tectonic plates
What is the oceanic crust?
The part of the Earth’s crust below the oceans.
What is the continental crust?
The part of the Earth’s crust that makes the continents
What are the differences between the continental crust and the oceanic crust?
Oceanic crust is thinner (5-10km thick) and denser than the continental crust.
Oceanic crust is recycled at destructive margins as it subducts under the continental crust.
Continental crust is thicker (20-200km thick) and is less dense than the oceanic crust.
Continental crust cannot be destroyed.
What is it called when two plates meet?
Plate boundary/plate margin
What are convection currents?
Circulating movements of magma in the mantle caused by the heat of the core
Why do tectonic plates move?
Powerful convection currents in the mantle drag them
Describe the global distribution of earthquakes
Earthquakes are distributed in long, narrow, linear belts at plate boundaries
Where are earthquakes concentrated?
Around plate boundaries
What is an oceanic trench?
Long, narrow depressions on the seafloor formed at some of the deepest points of the ocean
How many types of plate boundaries are there?
There are three types of plate boundaries: constructive, destructive and conservative
What occurs at constructive plate boundaries?
- Two plates move away from each other
- Magma from the mantle rises up to the surface
- Magma reaches the surface and cools to create new ocean floor
- The seafloor is ‘spreading’ (as plates are always moving apart)
- This creates volcanic islands and mid-ocean ridges
What occurs at destructive plate boundaries?
- When the oceanic plate is subducted underneath the continental plate, an oceanic trench is created
- The two plates lock ‘like a machine without oil’ and pressure builds up
- When this pressure is suddenly released, it sends shockwaves to the surface, causing an earthquake
- The oceanic plate continues to subduct and begins to melt because of heat and friction from the mantle
- This creates new magma which is lighter than the existing magma. This rises to the surface causing a volcanic eruption.
What occurs at conservative plate boundaries?
- When the plates slide past each other the two plates lock ‘like a machine without oil’
- Pressure builds up at the focus
- When this pressure is suddenly released, one of the plates jerk forward
- This sends shockwaves to the surface causing another earthquake
What are earthquakes measured on?
The Richter Scale
What is the strongest and weakest number?
9 is the strongest, 1 is the weakest
What is magnitude?
The size of an earthquake