Tectonic Flashcards
Name 3 types of tectonic natural hazard
- earthquakes
- volcanic eruptions
- tsunamis
What is the difference between natural hazards and natural disasters?
Natural disasters are when the natural hazards actually do affect people or their property
What causes the tectonic natural hazards?
The movement of the tectonic plates
Describe the inner core of the earth
A ball of solid iron and nickel
Describe the outer core of the earth
Very hot liquid
What is the mantle?
Semi molten rock moving very slowly around the earths core
What is the outer layer of the earth called?
The crust
How thin is the crust?
20km approximately
What are tectonic plates?
Areas of the crust divided into slabs
What do the tectonic plates float on?
The mantle
Name the two types of crust that the plates are made of
- continental
* oceanic
Describe continental crust
- thicker
* less dense
Describe oceanic crust
- thinner
* more dense
Why do the plates move?
The mantle underneath them is moving very slowly
What are the places where the plates meet called?
Boundaries or plate margins
What is a natural hazard?
A naturally occurring event that has potential to affect people’s lives
Name the 4 types of tectonic plate boundaries
- constructive
- destructive
- conservative
- collision
What happens at a collision plate boundary?
Two plates of similar densities push against each other
What do collision plate boundaries cause for the land between them?
The land between them rises up and form mountains
What natural hazards occur at collision plate boundaries?
Earthquakes and tsunamis
How are earthquakes formed at collision plate boundaries?
They push together with equal force so eventually one will give way and flick up, causing an earthquake.
When are tsunamis caused at collision plate boundaries?
If one of the plates is oceanic
What happens at destructive plate boundaries?
Two plates of different sizes/densities are moving towards each other
What happens when an oceanic plate and a continental plate meet at a destructive plate boundary?
The denser oceanic plate is forced down into the mantle and is destroyed
What natural hazards are often caused when an oceanic and continental plate meet at a destructive plate boundary?
Volcanoes and ocean trenches
What is an ocean trench?
Very deep sections of the ocean floor where the ocean plate goes down
Name an example of a destructive plate boundary
The Pacific and North American plate boundary
What happens at a constructive plate boundary?
The plates pull apart
What natural hazard is always formed at constructive plate boundaries?
Volcanoes
How dangerous are the volcanoes that form at constructive plate boundaries?
Not very, the erupt with very little force and often magma just rises and cools to form new crust
Name an example of a constructive plate boundary
The Eurasian and North American plates are moving away from each other at the mid Atlantic ridge
What is a subduction zone?
The area where an oceanic plate is being pushed under a continental plate
What happens when two continental plates meet at a destructive/collision plate boundary?
They smash together but no crust is destroyed
What happens at conservative plate boundaries?
Two plates are moving sideways past each other or moving in the same direction at different speeds
What is a fault line?
The place where two plates slide next to each other
What natural hazard is caused at conservative plate boundaries?
Earthquakes
Why do earthquakes occur at conservative plate boundaries?
The friction between the two plates moving build up and is released when they give way
Name an example of a conservative plate boundary
The Pacific plate moving past the North American plate on the USA west coast, at the San Andreas fault
What moves the mantle under the earths surfaces?
Convection currents, heats and rises due to extremely hot temperatures then cools and falls in a cycle
How hot is the earths core?
5500*c
How hot is the mantle?
1100*c
How are volcanoes formed at destructive plate boundaries?
The denser oceanic plate subducts under the continental plate and melts to make magma. The seawater also goes down with the plate which makes the magma less dense so it rises and erupts out of the earth as volcanic eruptions, the water gets very hot and can erupt as steam to make very explosive volcanoes
What comes out of volcanoes?
Lava (molten rock)
What happens when the oceanic plate sticks to the continental plate as it subducts? What does this cause?
Huge pressure can build up and when they finally give way a huge amount of energy is released and causes an earthquake
What are the gaps in volcanoes called that magma can rise up and out from?
Fissures
Which plate boundaries to volcanoes form at?
- destructive
* constructive
Which plate boundaries cause earthquakes?
- destructive
- collision
- conservative
- (constructive, not devastating)
Where are the most severe earthquakes usually found?
Destructive and conservative plate boundaries
What is an earthquakes focus?
The movement point of the rock
What is an earthquakes epicentre?
Directly above the focus on the earths surface
What are seismic waves?
The vibrations that cause an earthquake that start at the focus
How can we measure the magnitude of an earthquake?
Using the Richter scale and a seismograph
What type of scale is the Richter scale?
A logarithmic scale
What is a logarithmic scale?
When the value increases by 1, the magnitude increases by 10, eg 6 is 10x stronger than 5
What is the Mercalli scale?
Similar to the Richter scale but is based on observation instead of the seismograph
What are earthquakes caused by?
The pressure and friction that build up at all the types of plate boundary
How does pressure build up destructive boundaries?
Pressure builds up when one plate gets stuck as its moving down past the other into the mantle
How does pressure build up at constructive boundaries?
Pressure builds along cracks within in the plates as they move away from each other
How does pressure build up at conservative boundaries?
Pressure builds up when plates that are grinding past each other get stuck
What happens when the plates eventually jerk past each other?
They send out shock waves, vibrations