Tectonic Hazards Flashcards
What are the four layers of the earth called?
- crust
- mantle
- outer core
- inner core
What is the crust?
The layer surrounding the inner core
- it is a liquid layer
- made up of
What is the outer core?
The layer surrounding the inner core
- it is a liquid layer
- made up of iron and nickel
What is the mantle?
The widest section of the earth
- thickness of approx 2,900 kilometres
- upped part if mantle is named asthenosphere
- made up of semi - molten rock called magma
What is the inner core?
The centre and hottest part of the earth
- it is solid
- made of iron and nickel
- temperatures of up to 5,500 C
What are the two types of crust?
Continental and oceanic
What is the continental crust?
- typically 30- 50 km thick
- older than oceanic
- lighter than oceanic
- cannot be destroyed
What is the oceanic crust?
- only 5 - 10 km thick
- denser than continental
- can be subducted
- constantly being destroyed and replaced at plate boundaries
How do plates move via slab pull?
(Theory of plate tectonics)
Plates are extremely heavy so gravity acts upon them, pulling them apart
How do plates move via convection currents?
(Theory of plate tectonics)
- convection currents under the earths crust transfer heat
- this heat rises through the surface
- it then cools back down in a circular motion
- convection move the plates when the currents diverge near the earths crust
- when convection currents converge, plates move towards each other (ridge push)
Where are earthquakes located?
Mostly in long, narrow belts, all along toyed of plate boundaries ( or margins)
Do volcanoes and earthquakes occur in the same places?
Yes
- They often occur in similar places in narrow zones of activity
When are some common narrow zones of activity?
- the pacific ring of fire around the Pacific Ocean
- the mid-Atlantic ridge, a mod ocean ridge that extends along the floor of the Atlantic Ocean
- southern Europe
Where is an exception of volcanic activity?
The Hawaiian islands
- entirely volcanic in origin
- formed in the middle ld the Pacific Ocean
- located more than 3,200 km from nearest plate boundary
(Hotspot theory)
What is the hotspot theory?
There are fixed spots in the mantle where magma rises to the surface. As the crust is moved over these foxed spots, volcanoes are created, eventually forming a chain of volcanoes
What is the relevance of the pacific ring of fire?
Over 450 of the world’s active and dormant volcanoes are located here, but the area is also highly active in terms of earthquakes
- about 90% of all earthquakes happen in and around the pacific ring of fire
What do DESTRUCTIVE plate margins involve/do?
- Usually involve an oceanic plate and a continental plate
- plates move towards one another
What can destructive plate boundaries form?
- deep ocean trenches when oceanic plate sinks into mantle
- fold mountains (between two continental) as land will buckle and crumple upwards forming fold mountains
- volcanoes (subducting plate descends and melts due to friction and heat, forming magma)
What do destructive plate boundaries cause?
- earthquakes ( movement and friction between plates can cause earthquakes)
- volcanic eruptions ( magma that forms can erupt after rising to the surface)
- tsunamis ( earthquakes, especially underwater, can generate tsunamis)
What do CONSTRUCTIVE plate margins involve/do?
- typically involve two oceanic plates
- can also involve continental plates
- plates move apart from one another
What do constructive plate margins form?
- mid ocean ridges ( long underwater mountain chains where new crust is formed)
- shield volcanoes (with broad, gently sloping sides formed by the eruption of fluid lava)
- rift valleys (between continental plates, deep narrow depressions that form, as the crust stretches and fractures) e.g East African rift valley
What do constructive plate boundaries cause?
- can cause minor earthquakes
- volcanic eruptions ( when movement of plates causes mantle to overflow)
What do conservative plate boundaries involve/do?
- can involve both/either or continental and oceanic plates
- plates slide past each other horizontally or are side by side moving at different speeds
What do conservative plate margins form?
- movement of plates can create fault lines and other surface features
- e.g the San Andreas Fault is a fault line caused by conservative plate boundaries
What do conservative plate margins cause?
- Earthquakes ( as plates move friction occurs and plates become stuck, pressure builds up because the plates are trying to move. When pressure is released it sends out huge amounts of energy in the form of seismic waves causing destructive earthquakes since they are close to earths surface)
- no volcanoes at a conservative plate margin
What do COLLISION plate margins involve/do?
What do collision plate margins form?
What do collision plate margins cause?
What are the 3Ps in reducing impacts of earthquakes?
Predict, protect, prepare
How can animals predict earthquakes?
some animals are able to pick up on water/magnetic changes when an earthquake is close to occurring
How do seismographs predict earthquakes?
Can pick up in minor tremors occurring before the main event
How is a tiltmeter used to predict earthquakes?
Checks for any movement in the rocks
What features in buildings can be used to protect from earthquakes?
- shock absorbers to absorb ground shaking
- open areas outside of buildings for easy evacuation
- automatic shutters come down over windows to prevent broken glass falling
- rolling weights on roof to counteract shock waves
- walls reinforced with steel and concrete to reduce movement
- cross bracing to create a rigid, interconnected network within a buildings structure, extra support prevents swaying
What is the focus of an earthquake?
The point in the earths crust where seismic waves originate
What is the epicentre in an earthquake?
Directly above the focus on the earths surface
What are shockwaves of an earthquake?
Seismic waves generated by an earthquake that pass through the earths crust
What are the primary waves of an earthquake?
Waves travel fastest, causing back and forth movement
What are secondary waves in an earthquake?
Waves are slower and cause movement from side to side
What are longitudinal waves?
Waves cause up and down movement
What are transverse waves?
Waves which cause side to side movement, cause much damage
What is the Richter scale used for?
Measures the amount of energy released by an earthquake (the magnitude) using a seismometer
What is the scale of the Richter scale?
1-10 but there is no upper limit
It is a logarithmic scale which means that a size ‘6’ on the Richter scale is 10X larger than a size ‘5’ and 100X more powerful than a size ‘4’
What does the mercalli scale measure?
The effects of an earthquake
What is the scale of the mercalli scale?
I - XII
- uses subjective descriptions of resulting damage
I = barely felt
XII = total destruction
