The Restless Earth Flashcards
(26 cards)
What are the two plates doing at a constructive plate boundary and why
They are moving away from each other because convection currents are moving up from the mantle and then moving sideways
At a constructive plate boundary is land being made or destroyed
It is being made. Because as the convection currents move up some mantle material will harden on the sides of the plate creating new land
Is there a possibility of a volcano being formed at a constructive plate boundary
Yes. Because some mantle material that is being pushed up may push further upwards and form a volcano.
They are sometimes formed on the oceanic ridge under the water and erupt to build above the surface of the sea. Examples of volcanic islands are Iceland and Surtsey
What are constructive plate boundaries sometimes referred to as
Oceanic ridges because sometimes they are found in the middle of the ocean. For example the mid atlantic ridge.
What happens at all destructive plate boundaries
The plates move towards each other. At all destructive plate boundaries land is being lost
Explain what happens at a subduction zone. (A.destructive plate boundaries)
The convection current’s pull the two plates together.
Two plates of different densities. The plate with the greatest density sinks.
As it sinks into the mantle it will eventually melt due to the heat.
This adds less dense molten material to the mantle.
The point at which the oceanic plate sinks is called the subduction zone, and there will be a gap between the two plates which is called the oceanic trench
What will happen in a subduction zone as a result of the oceanic plate melting
Less dense molten material from the melted oceanic plate will rise.
Pressure in the mantle from sinking plate and steam from the seawater will create volcanoes.
Volcanic eruption is at this type of Boundry a very explosive.
Earthquakes occur here because the plates are rubbing together e.g. whether Nazca plate meets the South American
What happens at a collision zone (P.destructive boundary)
Both plates of the same density so neither can be forced under the other when convection current’s pull them together.
Both plates are forced upwards as they collide and so form fold mountains where the plates meet
E.g. the Himalayas-south of the Eurasian plate meeting the Indo Australian plate
What happens at conservative plate boundaries
Two plates sitting side-by-side and the convection current’s in the mantle make them slide past each other.
Is land gained or lost at a conservative plate boundary
It is not gained or lost
Give an example of a conservative plate boundary
San Andreas fault, San Francisco
Is there a possibility of earthquakes occurring at a conservative plate boundary
Yes because as this plates slide past each other the tension builds up and earthquakes can occur
Is there a possibility of volcanoes occurring at a conservative plate boundary
No
Give an example of a young fold mountain. And why they are taller than old fold mountains
Everest
They have not been exposed to as much as old fold mountains like Snowdonia
Where do you fold mountains form
At destructive plate boundaries.
-Can either be subduction zone is
e.g. where the Nazca plate and the South American plate meet. You get the Andes
- they also form at collision zone is where two plates meet up at the same density
Eg where the Eurasian and Indo Australian plate meet -the Himalayas are formed
What happens at a simple fold
It’s because when both sides have equal forces (very rare)
when fold mountains form, material collects in the hollow between the two plates called Geo synclines when the plates are pushed together, the geosyncline squashes the sediment, pushes up forming the fold
What are earthquakes formed by
Earthquakes are vibrations caused by earth movements at plate boundaries and the major the fault lines (cracks in the earth surface)
Where can earthquakes occur
At all for major plate boundaries
Most for severe earthquakes are normally found at Conservative (e.g. San Andreas) and destructive (Nepal) plate boundaries
What are the steps of a earthquake occurring at a conservative plate boundary
- Two plates cannot move past each other easily
- Plates become locked
- Friction causes pressure to build up. Suddenly the pressure is released and the plate jolt into a new position. This causes Seesmic waves. The vibrations are called earthquakes
What are earthquakes measured on
- The Richter scale
- Mercalli scale
The readings are collected by the UKGS (UK geology survey) and the USGS (US geology survey
Explain a bit about the Richter scale
- It is a logarithmic scale
- Every step up is 10 times greater than the one before
- It is an open ended scale
Explain a bit about the Mercalli scale
- It is a closed scale that goes from 1-12
- Based on observations
- Based on opinion
- Depends where you are when the earthquake happens (being closer and being further away. Being around buildings or not being around buildings)
What is the focus of an earthquake
The point within the crossed where the earthquake starts or originates
What is the epicentre of an earthquake
The point on the surface immediately above the focus
