Tectonic processes and hazards Flashcards
Stages of the hazard management cycle:
Mitigation (prevention), before
Preparedness (adaptation), before
Response, during disaster
Recovery, after disaster
Difference between hazard mitigation and adaptation:
Mitigation - strategies meant to avoid, delay or prevent hazard events
Adaptation - strategies used to reduce the impacts of hazard events
Movement of plates is driven by 4 processes:
.Mantle convection
.Slab pull
.Sub-duction
.Seafloor spreading
Seafloor spreading meaning?
Occurs in mid-ocean ridges. Hot magma rises up, hardens and forms oceanic crust.
This new crust pushes tectonic plates apart in process called seafloor spreading .
What is a mid ocean ridge?
Long underwater mountain range formed by lava eruptions through Earth’s crust
What is palaeomagnetism?
Every 400,000 years the magnetic fields in rocks change direction.
Palaeomagnetism confirms that seafloor is spreading
Difference between oceanic and continental crust
.Oceanic is denser and thinner
.Continental is thicker,less dense and older than oceanic crust
Where are tectonic plates formed and floating?
.Between crust and upper mantle, the solid lithosphere where tectonic plates are formed.
.In the semi-molten asthenosphere is where tectonic plates float.
How are intra plate earthquakes formed?
Plates move over a spherical surface, zones of weakness are created.
Intra plate earthquakes happen at these zones of weakness.
What are mantle plumes?
They exist below the tectonic plates and are stationary.
As tectonic plates move slowly over it, this produces chain of volcanic islands.
What is volcanic hotspot?
Hotspot is an area on Earth that exists over an isolated mantle plume in the upper mantle.
Magma plume causes melting and thinning of rocky crust and widespread volcanic activity creating an island arc (Hawaii is an example).
Divergent margin meaning and an example:
Plates moving away from each other
-On land Rift valleys are formed
-Ocean ridges which eventually form islands if underwater.
An example is Heimaey, volcanic island near Iceland. Rift valley is east African rift
What type of lava is produced at divergent plate margin and its features?
Very hot lava with low silica content so low viscosity (basaltic)
Convergent margin meaning and examples:
Plates moving towards each other
-Oceanic-continental: Composite volcano and deep sea trench formed (Nazca plate subducting south America plate forming Andes mountain range with many volcanoes, and Peru trench).
-Oceanic-oceanic: Deep sea trench formed (e.g. Mariana trench)
-Continental-continental: Fold mountains formed (Himalayas which grow 10 mm every year)
What type of lava is produced at convergent plate margin and features?
Cooler lava with higher silica content so more viscous. (Andesitic)
Lava is viscous so could block vents causing pressure to build and a violent eruption occurs.
Example of shield and composite volcano:
Shield volcano: Mauna Kea on Hawaii
Composite volcano: Mount St Helens in US
What is the benioff zone?
Area where deep earthquakes caused by friction of plate subduction occurs
Why are there no volcanoes in Himalayas?
Rock is too thick, Continental plate meets another continental plate
Rank earthquake waves from fastest to slowest:
1)Primary
2)Secondary
3)Love
Where does each earthquake wave focus its energy?
Primary: Travels through solids and liquids inside the earth
Secondary: Travels only through solids inside the earth
Love: All of its energy focused on Earth’s surface
What are aftershocks and why are they cause?
These are smaller earthquakes which occur for a period of time after an earthquake, occur as result of readjusting along part of the fault that slipped at time of main earthquake
Case study for aftershock:
In 2011 an aftershock struck Christchurch, New Zealand caused more damage and loss of life than main earthquake in 2010, in 2010 it was centered in rural area whereas in 2011 it was closer to the city
Definition of natural hazard, disaster and mega-disaster:
1)Natural hazard are events that have potential to harm people and property.
2)Disaster is when it has done the harm, Conditions include:
-10 or more deaths
-100 or more people affected
-USS 1 million in economic losses
3)Mega-disaster is where scale of impact may lead to requirement of international aid, occur rarely and affect large populations
Predicting volcanic eruptions:
Unlike earthquakes, scientists can often predict volcanic eruptions. Signs include:
-Small earthquakes, magma rising which break rocks, detected by seismograms
-Changes to the slope angle of volcano as magma moves inside, detected by tiltmeter
