Tectonic Processes and Hazards Flashcards
Trend, evidence and anomaly of location of volcanoes and earthquakes
Trend - lots of volcanoes and earthquakes along plate boundaries.
Evidence - Along north and South American
plates there are many active volcanoes and earthquakes
Anomaly - volcanoes and earthquakes where there is not plate boundaries - Pacific ocean
Oceanic plate
Newer, denser
Continental plate
Older, less dense
Example of a major crustal plate, minor and micro
•Major - African
•Minor - Cocos
•Micro - Sunda
What creates different types of plate boundaries
Plates moving in different directions and speeds
State and define the 3 plate movements
•convergent = coming together
•divergent = moving apart
•conservative = moving alongside each other
Define intra
Within
Define intra plate quakes
Occur away from a plate boundary, within the plate
Define active margins
A continental edge that is a plate boundary
Define passive margins
A continental edge that is not a plate boundary
A cluster of red dots is known as?
Episentric plate quakes
Why do scientists believe earthquakes happen at episentric plate quakes
Old faults within the rock
About earth’s crust
•Structure part: oceanic 7km thick, continental 70km thick
•Temp: about 400°C
•Density: Less dense (oceanic = 2.7g/cm3, continental = 3.3g/cm3)
•Composition: Granite (continental) and basalt (oceanic)
•Physical state: solid
•Earthquake (seismic) waves: Surface and body waves able to pass through
About mantle
•700km to 2890km deep
•Temp: 870°C
•Density: Less dense to medium density (3.3 to 5.4g/cm^3)
•Composition: Peridotite -> Upper = olivine, Lower = magnesium and solid in silicate
•Physical state: phases of liquid and solid in layers
•Earthquake (seismic) waves: Body wave pass through at variable rates due to density changes.
About outer core
•structure part: 2890km to 5150km deep
•temp: 4400°C to 6100°C
•density: Dense (9.9 to 12.3g/cm3
•composition: 12% sulphur 88% iron
•physical state: Liquid (+ generates a magnetic field)
•earthquake (seismic) waves: Only P waves able to pass through, an S wave ‘shadow zone’ created from about 105° from the focal point
About inner core
•structure part: 5150km deep to centre
•temp: 7000°C (Radioactive decay)
•density: Very dense (13.5g/cm3)
•composition: 20% nickel 80% iron
•physical state: Solid + radiates heat), maybe two parts with huge crystals aligned in opposite directions
•earthquake (seismic) waves: Only P waves read to the inner core and pass through, but their refraction at the core mantle creates a ring shadow zone between 105° and 140° from the focal point
Explain the 3 reasons plates move
•convection currents - mantle is heated closest to the core, the heated mantle rises, the mantle reaches the crust + moves under it, pulling it along, the mantle near the surface cools + sinks back to the core, completing the convection current
•slab pull - At subduction zones, the oceanic plates move into the mantle, this pulls the rest of the plate down with it, making it move faster. If a piece of the plate breaks off as it moves into the mantle, it melts and moves to the core, cooling down
•ridge push - At divergent plate margins, mantle that rises to the surface, pushes the plates apart, speeding up their movement
Explain the 4 plate margins
•divergent (constructive) - caused when two plates move apart, magma wells to the surface to fill the gaps left by the plates,
forming new crust
•convergent (destructive) - caused when the oceanic plate is subducted underneath the less dense continental plate. The oceanic plate melts as it reaches the subduction zone + can force its way to the surface as magma
•convergent (collision) - caused when two continental plates move towards each other. Fold mountains are created.
•conservative - caused when 2 plates move past each other in opposite directions or in same direction at different speeds
Explain the 3 different types of lava
•Andesitic Lava: 800-1000°C. Intermediate Silica (60%), gas content magnesium + iron. High water + hydrochloric acid. Low SO_2. gas content - 3 to 4%. Subducted oceanic plate melts + mixes with seawater, lithospheric mantle + continental rocks. Slow flow - intermediate viscosity traps gases. middle explosivity
•Rhyolitic lava: 650-800°C. high silica (70%) gas content 4-6%. potassium, sodium, aluminium + gas content. Low iron + magnesium. thick + stiff flow. very explosive
•Basaltic Lava: 1000-1200°C. Low Silica (50%), water, gases + aluminium. High CO_2, iron + magnesum. gas content low -
0.5 - 2% Thin+ runny flow. non explosive
Define lithosphere
Crust (rock part)
Define hypocentre
the focus point within the ground where the strain energy of the earthquake stored in the rock is first released. The distance between this + the epicentre on the surface is called focal length
Define epicentre
the location on the earth’s surface that is directly above the earthquake focus point where an earthquake originates
Define the 3 types of waves
•Primary wave: Arrives first, fast, moves through solid rock and fluids, pushes and pulls (compresses) in the direction that is travels.
•Secondary wave: Slower than P wave, only moves through solid rock, up and down movement.
•Love wave: Only travels through the surface of the crust, fastest of the surface waves and moves from side to side (horizontal) as it moves forward.
Definition and example of a hot spot
A small area of the Earth’s crust where an unusually high heat flow is associated with volcanic activity e.g. Yellowstone National Park
Define volcano
A volcano is a surface landform resulting from the extrusion of magma from underground
State and define Materials ejected by a volcano
•Jokulhlaup - catastrophic glacial outburst flood, rapid discharge of water, ice + debris
•Pyroclastic flows - Molten magma froths in the vent of the volcano - bubbles burst explosively + eject hot gases, pyroclastic material (glass shards, pumice, crystals + ash). The clouds can be 1000’C
•Lava - lava can be fast moving up to 15m/sec, can be viscous
•Tephra - when a volcano erupts + ejects material (rock fragments) into atmosphere
•Volcanic Gas - Water vapour, sulphur dioxide, hydrogen + carbon monoxide
•Lahars - volcanic mudflows - fine sand
+ silt material
Explain VEI
Volcanic Explosivity Index - measures the explosiveness of an eruption - open ended + ranges from 0-8
Define perception of the hazard
People’s judgements, beliefs and attitudes on the likelihood of the event
How can scientists predict/forecast volcanic eruptions
using Satelites (look for infrared radiation that indicates rising magma), ground instruments (measure gas emissions, ground deformation + resulting earthquake activity), evidence from past eruptions and hazard maps (indicate areas at greatest risk)
When do earthquakes become a hazard and what are the factors that influence this
An earthquake becomes a hazard when it impacts on people or on people’s activities. The factors that influence this are: tectonics + the global distribution of earthquakes, earthquake magnitude + depth, population density, building + structural vulnerability, extent of earthquake preparedness, levels of development and, nature of bedrock.
Where do earthquakes generally occur
At plate margins
How do we measure earthquakes
Using the Richter scale
State and explain the secondary hazards of an earthquake
•Soil liquefaction - water-saluated material - lose normal strength - behave like liquid under the presure of strong shaking. An earthquake can cause the water pressure to increase to the point where the soil particles can move easily.
•Landslides - slopes weaken + fail
•A tsunami - a series of larger waves usually caused by volcanic eruptions or underwater earthquakes
Define wavelength
distance between corresponding points of two consecutive waves
What causes a tsunami + definition + explanation
a single or series of waves generated by a sudden displacement of water in the ocean, can have massive wavelengths up to 100km, waves can be an hour apart + travel up to 800km/h - an earthquake happens under the sea - lifts up water - wave radiates outwards - starts low + large wavelength - shallow water - slow increase height - gravity collapses it - 5th wave could be largest
Wave shoaling
When tsunami waves increase in height when they reach shore
Factors affecting the impacts of a tsunami
•large events will cause more damage
•more distance = less effects
•shallow water = larger waves
•less impacts if coral reefs / mangroves
present
•night = more impacts - unaware
•tourism = more impacts - busier
undeveloped - poor quality homes.
Define hazard
a perceived natural event that has the potential to threaten both life and property
Define disaster
the reality of a hazard happening; when it causes a significant impact on a vulnerable population
