The Challenge of Natural Hazards: Tectonic Hazards Flashcards
Natural hazard
Natural hazards are extreme natural events that can cause loss of life, extreme damage to property and disrupt human activities.
There are 4 different types: geological, biological, meteorological and geomorphological.
Examples of geological hazards:
Earthquakes
Tsunamis
Volcanoes
Landslides
Examples of meteorological hazards:
Tropical storms
Drought
Wildfires
Extreme temperature
Examples of biological hazards:
Disease epidemics
Insect/animal plagues
Examples of geomorphological hazards:
Avalanches
Floods
Hazard risk
The probability of being affected by a natural event. Factors affecting hazard risk include location in world, stage of economic development, urbanisation, time of event and climate change.
Factors affecting hazard risk: vulnerability
- People living in coastal regions more at risk of tropical storms
- People in LICs less prepared for natural hazards
- People living in urban areas more at risk from earthquakes
- People living in low-lying areas more at risk from flooding
- People more at risk if an earthquake happens during rush hour
Factors affecting hazard risk: capacity to cope
HICs tend to be better prepared for natural hazards because they can monitor, predict and evacuate areas at risk. They also have enough money after a hazard for repairs and hospitals.
Factors affecting hazard risk: nature of natural hazard
- The higher a tropical storm is on the Saffir-Simpson scale, or an earthquake is on the Richter scale, the higher the risk will be
- If an earthquake at a destructive plate boundary caused a tsunami, more people would be at risk
Oceanic crust
Found underneath the oceans
Mostly made of igneous rock which is very dense
Thinner than the continental crust but heavier
Can be subducted
Continental crust
Has land on top of it
Mostly made of granite which has low density
Lighter than oceanic crust but also thicker
Floats higher on the mantle and doesn’t sink
Generally older than oceanic crust
Less often destroyed
Crust
The crust is the solid rock layer upon which we live. It is the outer layer of the Earth and also the thinnest. It is either continental or oceanic. The earth’s crust is broken into plates. Heat rising and falling inside the mantle creates convection currents generated by radioactive decay in the core. The convection currents move the plates.
Mantle
The mantle is the thickest section of the Earth and makes up for nearly 80% of the Earth’s volume.. The mantle is made up of semi-molten rock called magma.
Outer core
The outer core is the layer surrounding the inner core. It is so hot that it is always molten, also made up of iron and nickel.
Inner core
The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C.
Lithosphere
It’s made of the crust and the solid upper mantle.
Asthenosphere
The layer below the lithosphere where it’s less solid and convection happens.
Plate tectonic theory: convection
- convection currents occur in the mantle layer
- the molten rock is heated by radioactive decay in the core and then it rises
- when it meets the crust it cools and sinks back down
- this process repeats, either pulling the plates apart or pushing it together
Plate tectonic theory: ridge push
- When plates move apart at a mid-ocean ridge, magma rises from the mantle to create hot new rock (less dense so floats to top).
- As the rock cools and ages it becomes more dense (so sinks) and is pushed out of the way as new magma emerges behind it.
- This creates a ridge in the crust.
Plate tectonic theory: slab pull
- Because the oceanic plate is denser than the hotter mantle beneath it, it is heavier so gravity pulls it into the mantle.
- The process of a tectonic plate descending into the mantle is termed subduction.
Constructive plate boundary
- 2 plates move apart due to convection currents in mantle
- As the plates move apart, magma rises through crust then cools and solidifies
- Process repeats until new rock builds up, forming volcano
- Earthquakes can also occur
E.g. Mid Atlantic Ridge
Destructive plate boundary
- Denser oceanic plate is pushed under continental plate (subduction)
- Friction where the plates slide causes earthquakes and melts oceanic crust into magma
- Magma rises through gaps in continental plate and forms a volcano if it reaches the surface
E.g. Nazca plate forced under South American plate
What is the global distribution of earthquakes and volcanoes?
- Along plate boundaries.
- On the edge of continents.
- Around the edge of the Pacific.
(Earthquakes found along all types of plate margins.
Volcanoes only occur at constructive and destructive plate margins.)
Conservative plate boundary
- 2 plates slide past/move in same direction at different speeds
- Pressure builds along a fault
- Friction when the plates suddenly jerk free causes earthquakes
- No volcanoes
E.g. San Andreas Fault, California
