Tectonic hazards Flashcards
what is a natural hazard
naturally occurring event that threatens human lives and causes damage to property
tectonic and climate related
what is the internal structure of the earth
Crust, Mantle, Core, Lithosphere, Athenosphere
Crust: oceanic and continental, few km to 70km thick, Basalt and Granite
Mantle (solid rock, flow under high temp and pressure): 80% of volume, 800 to 3000C, 2900KM thick
Athenosphere: high temp and high pressure, rocks are close to MP so they are easily deformed
Core: 3500Km thick, Iron and Nickel, 3 to 5000km thick
Outer core (liquid): 2100km thick, Inner core (solid): 1400Km thick
Lithosphere: crust and uppermost mantle (rigid and brittle, float on softer athenosphere
describe the oceanic crust and continental crust
oceanic: beneath deep oceans, 5 to 8 km thick, basalt (heavy and dense, from magma that cools quick)
continental: beneath continental land masses and under shallow seas, 35 to 70km thick, lighter rock like granite, rock age varies (recent to 4 billion years ago)
how to plate tectonics move
- Convection currents are movements of heat within the mantle. Mantle is heated by the core and mantle material expands and rises, spreading out beneath the plates
- Plates are dragged along moving away from each other
- Hot mantle material cools and sinks pulling plates along
- Sinking mantle material gets heaten up near the core and 1 to 3 repeats
- Slab pull force is when the dense, sinking oceanic plate at subduction zones pull the rest of the plate behind it
- Subducting/sinking plate drives the downward moving portion of convection currents
- Mantle material is found away from where the plates subduct drive the rising portion of convection currents
- Draw the diagram and label
name all the types of plate boundaries
Divergent (O-O, C-C), convergent (O-O, C-C, O-C)
describe and draw oceanic oceanic plate divergence
- Two oceanic plates diverge, forming fractures at plate boundaries
- Magma rises and enters these fractures at zone of divergence, forming new oceanic floor, known as mid oceanic ridge
- Magma builds up and solidifies forming underwater sea volcanoes.
when they reach sea level, volcanic islands are formed
example: NA plate and Eurasian plate, mid-Atlantic ridge. Volcanic islands: Azores (North Atlantic Oceans) - Draw out the diagram
describe and draw continental continental plate divergence
- two continental continental plates diverge, then are stretched, causing fractures to form
- land in between the two continental plates sink, forming linear depressions known as rift valleys
examples: East African Rift System. African plate, Nubian and Somalian boundary diverge. Rift valleys of 30 to 60 km. Earthquake fractures and active volcanoes can be found along the East African Rift System
describe and draw continental continental plate convergence
- Two oceanic plates converge and collide. The denser oceanic plate subducts below below the other less dense oceanic plate
- This forms a subduction zone known as the deep oceanic trench
- The subducting plate causes mantle material above it to melt into magma
- The magma rises through the crust, forming volcanoes. And eventually an arc of islands form
- Earthquakes may occur as the converging plates result in high amounts of friction. Pressure is built up causing it to be released in the form of seismic waves, resulting in earthquakes.
Example: Pacific plate and and Philippine plate, pacific plate subducts under the Philippines plate. Mariana trench and Mariana Islands are formed - Draw the diagram
describe and draw continental continental plate convergence
- two continental plates collide and push against one another, resisting subductiuon as both plates are too thick and buoyant for subduction to occur.
- two continental plates converge and collide, and the crusts are compressed and massive folding occurs, upwards or sideways.
- As a result fold mountains are created
Example: Indian Plate and Eurasian plate, mountains formed are the Himalayas. - Draw the diagram
describe and draw oceanic continental plate convergence
- an oceanic plate converges with continental plate. The denser oceanic plate subducts under the less dense continental plate.
- an oceanic trench is formed at the point of subduction, while fold mountains are formed on the continental plate
- active volcanoes are formed on the continental plate when magma below the crust rises to the surface.
example: Near Sumatra, Australian Plate subducts under a section of the Eurasian plate, forming the Sunda trench. Barisan mountains are formed on the continental Eurasian Plate. - Draw diagram
describe transform plate boundaries
- plates slide over each other along transform plate boundaries, movement results in the formation of a transform fault .
- tremendous stress builds up and is released as earthquakes
example:
San Andreas fault, between Pacific and NA plate.
1906: earthquake occured in South California along the San Andreas fault.
several hundred kilometers of NA plate moved an avergae of 2.5m, even up to 7km.
describe fold mountains
- layers of rocks when compressed and folde mountains. eg: Himalayas
Formed at convergent plate boundaries , plate move towards each other and collide.
compressional forces create immense pressure, causing layers of rock to buckle annd folding.
upfold: anticline
downfold: syncline
with increasing compressional forces on one limb of a fold, rocks buckle til fractures form.
Draw diagram
Rift Valleys and block mountains
At divergent plate boundaries, where plates are pulled apart.
Fault: a fracture in the rocks which are displaces
Tensional forces from movements results in parts of the crust being fractured.
Rift valley: valley with steep sides, draw diagram
Block mountain: tensional forces are formed between a pair of parallel faults. Block mountains are blocks of lands with steep slopes, standing higher than surrounding land
example: Found at divergent plates, somalian and nubian boundary in african plate.
