Tectonic Hazards Flashcards
What are the 3 types of material that can be ejected from a volcano?
Gas
Solids
Liquids
Examples of gas to be ejected from a volcano?
Carbon monoxide
Hydrogen sulphide
Sulphur dioxide
Chlorine
Examples of solids to be ejected from the volcano?
Ash, dust, glassy cinders
Blocks of solidified
Pumice stone
Examples of liquids ejected from a volcano?
Lava bombs- tephra or pyrolasts.
Which solidify in air- eg pumice
Who was the first to consider the structure of the Earth and when?
The Greek philosopher Plato
2000 years ago
Who came up with the first theory, when and what was it?
Edmund Halley
1692
The earths structure was made of hollow spheres
What shape is the earth?
A geoid
Bulged around the equator and flatter at the poles
Why is the earth shaped the way it is?
Due to centrifugal forces.
These are generated by the earths rotation, this forces the molten interior outwards
Description of the crust.
Thin-
5-10m beneath the oceans to nearly 70km beneath the continents
What are the two types of crust?
Oceanic and continental
Description of oceanic crust?
Broken layer of basalt rocks
Sima- made up of silica and magnesium
Description of continental crust?
Bodies of granite rocks
Sial- silica and aluminium
Difference between Sima and Sial?
Sial is much thicker and less dense.
What is the lithosphere?
What the crust and upper mantle makes up.
Where tectonic plates are formed.
Description of the mantle?
Widest section- 2900km
Silicate rocks are in a thick liquid state which becomes denser the deeper you go.
Why is the mantle a liquid state?
Due to the great heat and pressure within this zone.
What is the asthenosphere?
A layer of softer almost plastic like rock.
Moves slowly carrying the lithosphere on top.
Describe the core temperature?
Centre and hottest part- above 5000 degrees C
What is the core made from?
Iron and Nickel
Is the core more dense than the crust?
Yes the core is 4 times denser than the crust
How many parts make up the core?
2- outer and inner
Describe the inner core?
Solid and made up of an iron nickel alloy
What is thought to create the earths magnetic field?
The spinning of the liquid outer core when the earth rotates
Describe the outer core?
Semi liquid and consists mostly of iron
What does the cores heat generate?
Convection currents in the mantle that spread very slowly within the asthenosphere.
What causes convection currents?
Radioactive decay of elements in mantle and core- e.g Uranium
How do the convection currents cause movements?
The current in the asthenosphere create drag on the base of the tectonic plate.
How is new crust created?
When convection currents diverge. Magma plumes rise and cool to form new crust.
Describe sea floor spreading?
When convection currents diverge beneath an oceanic plate. It created structures called mid-ocean-ridges. Ridges of higher terrain on either side of the margin. Eg- mid Atlantic ridge.
Describe mid-ocean ridges?
Chains of submarine mountain ridges with regular transform faults across the ridges at right angles to the boundary. Can rise up to 4000m.
Alfred Wegner info
In 1912 proposed continental drift
Pangea
Based theory on geological evidence and fossil records.
Couldn’t back up with a mechanism
When did more plate tectonics theory come to light?
1950’s- palaeomagnetism
1960’s- sea floor spreading
Geological evidence example 1
Glacial deposits and striations (rock scratches) in Brazil match those in west Africa
Geological evidence example 2
Matching rock sequences of age and composition linking Scotland and Canada.
How does geological evidence support continental drift?
These rocks and mountains must’ve formed under the same conditions to match- this would only be possible if the continents were once joined
Evidence for Continental drift?
Geological
Climatic
Biological
Jigsaw
Fossil record example?
Mesosaurus (reptile) found in Brazil and South west Africa.
Glossopteris (plant) found in South America, Africa, India and Australia.
Living species example?
Earthworms from the same family found in New Zealand, parts of Asia and North America.
Climatic example?
Coal which is only formed under warm wet conditions has been found beneath the Antarctic ice cap. This can only be explained by Antarctica being once positioned in warmer latitudes.
Process when oceanic plate combines with continental?
Subduction
Which plate is denser?
The oceanic plate
Which plate subducts?
The oceanic plate
Where is the exact point of collision at a destructive margin?
The bending of the oceanic plate- deep open trench
Give an example of a deep ocean trench?
Peru- Chile trench along the Pacific Coast of South America
What happens to the continental plate when it meets an oceanic plate?
The continental land mass is uplifted, compressed and buckled and folded into chains of fold mountains
Example of fold mountains?
Andes
What happens to the oceanic plate after subduction?
Melts at depths beyond 100km and completely destroyed by 700km.
Where is the zone where melting occurs of the oceanic plate?
Benioff zone
What is the melting of the oceanic plate caused?
Increasing heat at depth and the friction between the plates
What may friction create?
Tension and stresses building up, may be released as deep focus earthquakes
What happens to the oceanic plate once it’s been melted?
Creates magma- less dense than the asthenosphere
Rises in plumes
Through faults in the buckled plate
What occurs when two oceanic plates meet?
The faster of denser subducts
What is formed when two oceanic plates meet?
Deep ocean trench
Rising magma from Benioff zone forms crescents of submarine volcanoes which may form Island arcs
Give an example of a trench formed by two oceanic plates colliding?
Marinas trench
Pacific subducts under Philippine
Why does subduction not occur when two continental plates meet?
Both plates are of lower density than the asthenosphere beneath them
What is formed when two continental plates meet?
Sediment between them becomes uplifted and buckle to form high fold mountains.
Example of a fold mountain?
Himalayas
What else occurs when 2 continental plates collide?
Shallow focus earthquakes
Describe a conservative plate margin?
Friction
Stress builds when sticking occurs.
Stresses released as shallow focus earthquakes
Example of a conservative margin?
San Andreas fault
Earthquake example along the San Andreas fault?
LA Northridge 1994
What are the two kinds of plate divergence?
Oceanic- sea floor spreading
Continental- rift valleys
How are rift valleys formed?
Lithosphere stretches, fractures into parallel faults
Describe rift valleys?
Sets of parallel faults
The land between the faults collapse into deep, wide valleys which are separated by upright blocks of land called horsts
How are hotspots formed?
Concentrated decay in the core. Localised thermal currents- plumes rise vertically.
Plumes burn through the lithosphere
Movement of plate results in chain
Facts about Hawaii?
Pacific plate moves north west at a rate of 5-10cm per year
Shield volcanoes- runny lava
Benefits of volcanoes?
Lava flows create new land
Geothermal power from hot rocks
Igneous rocks contain valuable minerals- gold, silver, copper and diamonds
What are the 3 intrusive volcanic features?
Dykes
Sills
Laccoliths- batholiths
Describe dykes?
Where the magma solidifies in a fissure (vertical crack)
What can dykes form?
More resistant- prominent wall like features
Less resistant- ditch like features