The Reestless Earth Flashcards
Describe the crust
Very thin (But can vary between 6-70km)
Describe the mantle
Molten
Describe the outer core
Liquid
Made mainly of iron
Describe the inner core
Solid 5500oC hottest part
Made of iron
What are the two types of crusts?
Continental crust and oceanic crust
Describe the continental crust
Thicker Older Permanent Floats Less dense
Describe the oceanic crust
Thiner Younger Destroyed and remade Sinks Dence
What are the plate boundaries?
Destructive (subduction zone)
Destructive (collision)
Constructive
Conservative
Describe the destructive (subduction zone)
Oceanic plate meets continental plate. The oceanic plate subduction under the continental plate because it is denser. As the plate subducts it starts to melt due to the friction caused by the movement between the plates, these plated plate is know hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano
Describe the destructive (collision) plate boudary
When 2 plates of similar density move together (i.e. a continental plat and a continental plate). This causes the material between them to buckle and rise up, forming a fold mountain
Describe the constructive plate boundary
Convection current in the earth’s mantle forced the plates at the boundary apart. New continental crust is creat which can emerge ass volcanic island. The plates move approximately 3cm a year
Describe the conservative plate boundary
Conservative plate boundaries exist where two plates do not directly collides but slide past each other along a fault (weakness)
What is the landform for destructive (subduction zone) plate boundaries and does it cause earthquake?
Fold mountains
Ocean trench
Both earthquakes and volcanoes may be present
What is the landform for destructive collision plate boundaries and does it cause earthquake?
Fold mountains
Earthquakes with high magnitude
What is the landform for constructive and does it cause earthquake?
Shield volcanoes
Earthquakes with low magnitude
What is the landform for conservative plate boundaries and does it cause earthquake?
There is no volcanic activity at this plate boundary. However, huge amounts of pressure build up between the 2 plates therefore earthquakes are common with high magnitude
Give an example of a destructive (subduction zone ) plate boundary
The Pacific plate subducts under the Eurasian plate.
This causes many large earthquakes in Japan
Mount St. Helen volcano-Juan de Fuca (oceanic) and North America (continental)
Give an example of a destructive (collision) plate boundary
The Himalayas are an example of a chain of fold mountains. They have been formed the Indian plate colliding with the Eurasia plate
Give an example of a constructive plate boundary
The mid-Atlantic Ridge. North America and Eurasia plate
Give an example of a conservative plate boundary
The San Andreas fault in California.
North American plate and Pacific plate
What are fold mountains?
They are mountains formed from the folding of the earth’s crust. They are formed when 2 plates move together and force sedimentary rocks upwards into a series of folds
What are ocean trenches?
They is a long narrow steep-sided depression in the earth’s oceanic crust, usually lying above a subduction zone
When do earthquakes occur and were the they occur?
They occur where 2 areas on the earth’s crust try to move in different direction or at different speeds. If friction prevents these movement between the two areas, then pressure will build up. When pressure is eventually released by a sudden earth movement, the result is an earthquakes. Earthquakes can therefore occur at collision, ditructive, conservative and constructive plate boundaries.
How are earthquakes measured?
They are measured on the Richter scale and the mercalli scale. The Richer scale is logarithmic. This means that each level of the magnitude is ten time greater than the level below it.
What is the focus?
It is the exact location of an earthquake
What is the epicentre?
The point on the earth’s surface directly above this focus point
What are the primary effects of an earthquake?
They are the effects of the earthquake that happen as soon as the earthquake occurs
What are the secondary effects of an earthquake?
They are the knock on effects of the earthquake that occur after the earthquake such as fires
What are the different parts to the earth?
Crust
Mantle
Outer core
Inner core
How do you manage an earthquake?
Prediction
Protection
Preparation
What is prediction? (In terms of earthquakes)
Virtually impossible to know when an earthquake is going to occur
Animal behaviour may change before a big earthquake e.g In chania 1975 conducted evacuation following storage animal behaviour. Before a 7.3 earthquake hit
Where there are plate boundaries (80% of earthquakes occur at plate boundaries) , seismic mapping
Small tremors may lead to a big earthquake
What is protection? (In terms of earthquakes)
Intelligence anti-earthquake beds
Roads to provide quick access fore emergency
Building can be built to a standard to withstand earthquakes:
-open areas where people can assemble if evacuation
-Fire-resistant building material
-computer-controlled weights on roof to reduce movement
-‘birdcage’ interlocking steel frame
-foundations sunk into bed rock, avoiding clay
What is preparation? (In terms of earthquakes)
Organising activities and drills so that people know what to do in the event of an earthquake
Education-informing people what to do (e.g. schools, hospitals)
Sirens
Drop, cover, hold
Crust is neither formed or destroyed at a plate margin, what type of plate is it?
Conservative
Formation of volcano 1 (constructive plate boundary)
2 plates of oceanic crust, moving apart at a tensions plate boundary
Magma rising upwards from the magma chamber
Magma plugs gap in between plates adding new rock
Some magma may be forces along fault/vents and erupt at surface
Magma reaching surface as lava adds new layer onto surface of the volcano
Many eruptions may cause volcano to emerge from cords as volcanic Islands
An example is Iceland
Formation of volcano 2 (destructive plate boundary)
2 plates of continental crust and oceanic crust are moving together at a compressional plate boundary
Melting of oceanic crust creates heat which can force magma to surface through fault/crack
Oceanic crust is forced under continental crust at a subduction zone
Magma reaching surface as lava adds new layers onto surface of volcano
E.g. Mt Versuvius,Italy
What is volcano?
It is a cone-shaped mountain or hill, formed by eruptions of lava and ash
What happens in the magma chamber?
The magma chamber is a collection of magma inside the Earth, below the volcano
What is the main vent?
The main vent is the main outlet for the magma to escape
What is the secondary vent?
They are smaller outlets through which magma escapes
What is the crater?
The crater is craters after an eruption blows the top off the volcano
When does a volcanic eruption occur?
An eruption occurs when pressure in the magma forces up magma up the main vent, towards the crater at the top of the volcano. Some magma/lava will also be forces out of the secondary vent at the side of the volcano
Describe a cone/composite volcano
These are usually found at destructive boundaries
Cano volcanoes are narrow and steep-sided
Cone volcanoes are formed by eruptions of thick, viscous (sticky) lava
The thick lava moves relatively slowly and hardens quickly to form new rock - this explains the formation of a cone shape
Eruptions tends to be violent
Describe a shield/basic volcano
These are usually found at conservative boundaries
They are wide, with settle sloping sides
Shield volcanoes are formed by eruptions of runny lava
Eruptions here tend to be frequent but relatively gentle
Difference between the plate boundary formation between a compasit/cone shaped volcano and a shield/basic lava volcano
Cone destructive
Shield constructive
Difference between steep or gentle sided between a composite/cone shaped volcano and a shield/basic lava volcano
Cone
Steep
Shield
Gentle
Difference between viscous or runny between a composite/cone shaped volcano and a shield/basic lava volcano
Cone
Viscous
Shield
Runny magma
Difference between explosive to gentle eruption between a composite/cone shaped volcano and a shield/basic lava volcano
Cone
Explosive
Shield
Gentle eruption
Difference between ejected material between a composite/cone shaped volcano and a shield/basic lava volcano
Cone
Quickly cooling lava
Shield
Slowly cooling lava
Example of a composite/cone volcano
Mt St Helens
Example of shield lava volcano
Mauna Loa
What is needed for a tsunami?
Destructive plate margin
High magnitude
Shallow focus
What causes tsunamis?
Volcanic eruption-material out of volcano could fall into ocean cause big currents
Earthquake
Meteor
Land slide going into the sea
What is the formation of a tsunami?
Usually (70%) triggered by earthquakes
The crust shifts (primary effect)
A knock-on (secondary effect)
Causing the displacement of water above the moving crust
Differences between normal waves and tsunamis
Normal wave may have a length of 100m from crest to crest, tsunami = 200km
Height: normal waves are much shorter than tusnamis
Breaking waves smaller for normal waves
Move further onto land-tsunami
Faster-tsunami
What is super volcano?
It is a volcano that erupts with massive volume of material, much more than a normal volcano - at least 1000km3 of magma
What do supervolcanoes look like ?
They have large depression called calderas, often marked by a rim of higher around the edges
Positive of a volcanic eruption
The dramatic scenery created by volcanic eruptions attracts tourists. This brings income to an area.
The lava and ash deposited during an eruption breaks down to provide valuable nutrients for the soil. This creates very fertile soil which is good for agriculture
The high level of heat and activity inside the Earth, close to a volcano, can provide opportunities for generating geothermal energy.
Human and natural landscapes can be destroyed and changed forever.
Negatives of a volcanic eruption
Many lives can be lost as a result of a volcanic eruption.
If the ash and mud from a volcanic eruption mix with rain water or melting snow, fast moving mudflows are created. These flows are called lahars.
Lava flows and lahars can destroy settlements and clear areas of woodland or agriculture.
How do super volcanoes form at hotspots?
Magma rises up through cracks in the crust to form a large magma basin below the surface.
