The Restless Earth Flashcards
Describe the characteristics of the Earth’s CORE:
7000 degrees, solid iron and nickel ball.
Describe the characteristics of the Earth’s MANTLE:
Semi-molten rock, moves very slowly and has convection currents. Tectonic plates float on top of it.
Describe the characteristics of the Earth’s CRUST:
20km thick, divided int plates. Two types of crust: continental and oceanic.
Why do the plates move?
There are convection currents in the mantle nderneath
Describe the characteristics of continental crust:
Made of granite, much older (up to 3.8 billion years old), less dense, not renewable, can’t be destroyed, much thicker.
Describe the characteristics of oceanic crust:
Made of basalt, much younger (less then 200million years old) more dense, renewable, can be destroyed, much thinner.
Name at least 3 major tectonic plates
- Pacific
- North American
- Indo Australian
- Eurasian
- Nazca
- African
Name the 4 types of plate boundary:
- Constructive
- Destructive
- Conservative
- Collision
Describe what happens at a Constructive plate margin:
2 plates move away from each other, leaving a gap for magma to rise up through.
Describe what happens at a Destructive plate margin:
Oceanic crust descends below less dense continental crust. It is melted due to friction, forming magma, which can then rise through holes in the continental plate and form volcanoes.
Describe what happens at a Conservative plate margin:
Two plates move past each other in a parallel motion.
Describe what happens at a Collision margin:
Two plates of the same density are pushed together. Because neither one can be subducted, they buckle and form fold mountains.
At which plate margin(s) will you find earthquakes?
All of them.
At which plate margin(s) will you find volcanoes?
Constructive and Destructive.
What are the 4 pieces of evidence for Wagner’s continental drift theory?
- Fossil evidence
- ‘Puzzle fit’
- Paleomagnetism
- Mineral patterns
At which 2 boundaries can fold mountains form?
Destructive and collision
Why can fossils of sea creatures sometimes be found at the summits of fold mountains?
If there is sea between two plates as they move together at a collision boundary, sediment from the sea floor can be pushed up when the two plates come together, and as they’re compressed into sedimentary rock to form the fold mountains, fossils are also formed.
Name some human uses of fold mountains:
- Agriculture
- Hydro electric power
- Tourism
- Settlement
- Railways
- Quarries
What is the focus of an earthquake?
The point int he Earth’s crust where the seismic waves originte
What is the epicentre of an earthquake?
The point on the Earth’s surface directly above the focus, where the shock waves are strongest.
What are primary waves?
The first seismic waves to reach a seismograph, as they have the highest velocity.
What are secondary waves?
The seconds waves to reach a seismograph, they travel slower through rock.
What does the Richter scale measure?
The amount of energy released by an earthquake, using a seismometer.
What is the Richter’s scale?
1-10 for magnitude, but there is no limit on how high it can go. It is a logarithmic scale.
What does the Richter scale tell you?
It is logarithmic, so a 6 is 10 times more powerful than a 5, and 100 times more powerful than a 4.
What does the Mercalli scale measure?
Th damage caused to an area by an earthquake.
What is the Mercalli’s scale?
1-12, or I-XII as it is usually written in Roman numerals.
What does the Mercalli tell you abut an earthquake?
It uses subjective opinion, so different people have different opinions on where on the scale the earthquake is.
What are the advantages and disadvantages of the Richter scale?
- It is accurate, and results are produced by a machine
- Based on scientific fact, rather than opinion.
- Expensive, so not available to LEDCs
- Must be a seismograph in place to take a reading
What are the advantages and disadvantages of the Mercalli scale?
- It is free, so available to all countries
- Gives people n idea of how much damage was done compared to to other earthquakes
- Can be inaccurate, as it is based on one person’s opinion on one day
- Can be biased or inaccurate.
How can animals help predict earthquakes?
Possibly by picking up on water or magnetic changes
How can seismographs help to predict earthquakes?
Can pick up small tremors before an earthquake
How can tilt-metres help to predict earthquakes?
They check for any geological movements
What is a tsunami?
A wave train or series of waves where the entire depth of the ocean is set in motion by an event such as a n earthquake.
How do tsunami waves form?
The plates at a boundary under the sea flex, displacing an entire column on water vertically. The water then splits in two with one wave travelling in each direction.
How far apart can tsunami waves be?
200km, compared to 100m for normal waves
How high can tsunami waves get as they come inland?
Up to 30m
What is a lahar?
A mud flow triggered by a volcanic eruption
What is a pyroclastic flow?
A fast moving flow of ash and gases from a volcano
Name 3 features of a volcano:
- Main Vent
- Crater
- Parasitic Cone
What are Stratovolcanoes?
Steep sided, symetrical cone shape volcanoes formed by viscous lava that won’t flow very far. This means that the lava builds up around the vent
What are shield volcanoes?
Much flatter cones with gentle slops and wide bases. Formed by runny, less viscous lava.
What is a supervolcano?
A huge underground magma chamber, which could erupt at least 1000km3 of material, and have a detrimental global impact.
What is a fissure vent?
As magma rises, it tries to find the easiest route out through the surface. A fissure vent occurs when magma rises through a long crack and escapes
What are some of the benefits of volcanic activity?
- Geothermal energy
- Ash makes soil more fertile
- Tourism
- Rocks and Minerals
What is a caldera?
The depression of a supervolcano making a collapsed magma chamber
What is a ‘hot spot’?
A section of the Earth’s crust where plumes of magma rise, weakening he crust. These are away from late boundaries.
