tectonic processes and hazards Flashcards
what are volcanoes?
openings in the earth’s crust where gas, lava and ash erupt. Tectonic plates cause pressure to build up and magma and gases rise up reaching the surface
why do volcanoes get bigger over time?
lava cools - forms rock - so as the volcano continues to erupt over time it gets bigger, as the rock builds up
lava flows
- very hot (1000 degrees Celsius)
- move slowly (can be outrun)
- destroy everything in their path
pyroclastic flows
- hot rock, lava and ash
- move at a very fast speed (cannot be outrun)
tephra and ash falls
- volcanic rock and ash that erupt
- cause injury and death
- poor visibility
- slippery roads
gas eruptions
- magma contains dissolved gases that release into the atmosphere
- they can travel thousands of miles
lahars
- masses of rock, mud and water travel down sides of volcano
- caused when eruption melts snow or ice
- too fast to outrun - deadly
what are hotspots?
- volcanoes that occur in the middle of plate margins
- plumes of hot magma rise up and erupt
how is a chain of volcanic islands formed?
- as the plates move over the hotspot, the volcano is carried away with it and a new one forms
measuring the size and magnitude of volcanoes?
The explosivity index
- height and amount
- duration of eruption
- qualitative terms
predicting eruptions
- scientists can detect rock that breaks due to magma using seismograms
- surface changes shape
- changes to the tilt of the volcano
what is an earthquake?
An earthquake is the result of a sudden release of stored energy in the Earth’s crust that creates seismic waves.
hypocentre / focus
the point inside the crust from which the pressure is released
epicentre
the point on the surface directly above the focus
What is mantle convection?
Heat produced by the decay of radioactive elements in the Earth‘s core, heats the lower mantle creating convection currents
What is slab pull?
Newly formed oceanic crust at mid ocean ridges becomes denser and thicker as it cools. It then sinks into the mantle
Subduction?
One plate (oceanic) sub ducts underneath the other, and sinks into the mantle.
Sea floor spreading
When magma is forced up from the mantle in mid ocean ridges, new oceanic crust is created. This new crust pushes plates apart
Describe the features of
- inner core
- outer core
Inner - hottest part (mostly solid) 6000•c Iron
Outer - semi molten (iron and nickel) 4500-6000•
What is the mantle?
The widest layer.
Surrounds the core of the earth
Between outer layer and crust
What is the difference between oceanic crust and continental crust?
Oceanic - more dense but thinner and lines the ocean floors
Continental - older and thicker
Makes up the lithosphere
Covers all continents
Oceanic + continental (destructive)
- Oceanic plate is subducted
- fold mountains created as a result of the collision
- earthquakes caused by friction
- volcanoes formed because of melting of the oceanic crust in the mantle
Oceanic + oceanic (destructive)
The denser oceanic plate is subducted
- rise up to form separate island volcanoes
- shallow deep focus earthquakes formed here and are very powerful
Continental + continental
AKA COLLISION MARGIN
- sediments crumple up to form high fold mountains
- compression can cause shallow focus earthquakes which are extremely powerful
What are mid ocean ridges and how are they created?
Underwater mountain ranges across the ocean floor. They are created from rising magma that erupts onto the sea floor creating new land
What are rift valleys?
When the plates move apart, the crust stretches and breaks into a set of parallel cracks (FAULT) the land then collapses
Conservative plate margins
Plates sliding past each other.
Include transform faults
Powerful earthquakes as major pressure can build up from plates that get stuck
(Eg San Andreas fault)
Natural hazard?
Naturally occurring process that has the potential to affect people
Natural disaster
Major natural hazard that causes significant social, environmental and economic damage
Vulnerability
The ability to anticipate cope with, resist, and recover from a natural hazard
What does a seismometer do?
Detects ground movement
Moment magnitude scale factors?
- size of seismic waves
- rock movement
- area of fault broken by EQ
- resistance of rocks affected
What does it mean by a logarithmic scale?
Each number is 10 times the magnitude of the last number
What does the term magnitude mean?
The amount of energy released at the epicentre
What does the Mercalli intensity scale include
Observations from people who experience the earthquake.
Rated on a scale from 1 to X
Ground shaking effects
Causes infrastructure to collapse resulting in injury and death
Crustal Fracturing
The earths crust cracks leaving gaps
What is liquefaction?
Violent shaking can cause rocks to the strength and become more liquid than solid. Therefore buildings can lose their foundation and collapse
What is an intraplate earthquake?
They occur in the middle of plate margins far from the Boundary
What is the tsunami?
A Sunami is a series of larger than normal waves, which are usually caused by volcanic eruptions or underwater earthquakes
Define the term water column
The area of seawater from the surface to seafloor
Impacts of tsunami
- sweeping away buildings + people
- wash away soil destroying everything
- change the landscape
Why can’t we predict Tsunamis
Because we can’t predict earthquakes therefore we can only send out warnings
What are early warning systems?
Use Seismic sensors to detect undersea earthquakes
What does the DART system monitor?
It monitors changes in sealevel pressure. When Sunami waves are detected, the system sends the information through a satellite for warning systems
Benioff zone
This is where major friction is created due to the colliding of plates, often resulting in earthquakes
p waves
primary/pressure waves
- fastest
- travel through solids and liquids
- shake in a back and forwards motion
S waves
secondary waves
- slower
- only travel through solids
- move sideways at right angle to direction
- more damaging than p waves
L waves
Love waves
- slowest
- most damaging
- shake from side to side
- focus all energy on earths surface
how can a countries governance increase its vulnerability?
- building codes are often skipped
- quality of infrastructure
- efficiency of emergency services
- level of corruption
- how educated communities are on response
How can economic and social conditions increase its vulnerability?
- more wealthy = able to afford protection
- poor quality housing cannot withstand hazards
- poor health care can cause disease outbreaks
how can physical and environmental conditions increase vulnerability?
- high population density - more people at risk
- rapid urbanisation - poor quality housing as it has been rushed due to high demand
- if the accessibility of an area is difficult, it may delay emergency services
