Hazards - 1.1-1.3 Flashcards
How are earthquakes distributed globally
- usually occur along plate boundaries (most powerful found at conservative boundaries)
- intraplate earth quakes occur near the middle of plates usually due to pre-existing weaknesses
How are volcanoes distributed globally
- mainly found on convergent boundaries except from hotspot volcanoes
- hotspots such as Hawaii occur due to mantle plume
- around 70% of earthquakes found in the ring of fire
What are the four layers of the earth and their composition
- inner core (solid)
- outer core (liquid)
- Mantle (solid but elastic)
- Crust (solid)
What are the 3 layers of the mantle starting from shallowest and their composition
- Lithosphere (cool and brittle)
- Asthenosphere (ductile due to less pressure)
- Mesosphere (solid due to higher pressure)
What are convection currents and how do they work
- the cores hot temperatures causes magma to rise in the mantle and sink towards the core when it cools
- the currents flow beneath the lithosphere building up lateral pressure carrying the plates with them
What is slab pull theory
- at destructive margins the denser oceanic crust sinks into the mantle under the influence of gravity which pulls the rest of the plate along behind it
What is sea floor spreading
- mid ocean ridges are formed when hot magma is forced up from the asthenosphere and hardens forming new oceanic crust
- the crust pushes the tectonic plates apart in this process of sea floor spreading
What happens during subduction
- as new crust is being created in one places its being destroyed in another by subduction
- as two plate move towards each other, (oceanic and continental), the oceanic will slide under the continental into the mantle where it melts in the subduction zone
What is paleomagnetism
- when the earths magnetic fields change direction causing the poles to swap
- when lava cools, minerals inside the rock lineup with earths magnetic direction
What is an intraplate earthquake
found in the middle of tectonic plates caused by stress within a plate. Since plates move over a spherical surface zones of weaknesses are created
What are hotspot volcanoes (mantle plumes)
Area in the mantle which heat rises as a hot thermal plume. High heat and low pressure at base of lithosphere enable melting of rock which rises through cracks in rocks causing volcanoes
What is magnitude and intensity
Magnitude: measures the amount of energy released from the epicentre
Intensity: a measure of the ground shaking
Describe the process of earthquakes
- movements are preceded by a gradual build up of tectonic strain which stores elastic energy in rocks
- when pressure exceeds the strength of the fault the rock fractures
- this produces the sudden release of energy, creating seismic waves
- the crust rebounds either side of the fracture (ground shaking) that is the earthquake felt on the surface
What are the features of a body P-wave
- fastest and first to be received
- compressional wave
- travel through solid and liquid
What are the features of a body S-wave
- slower - arrive after p wave
- up and down / side to side motion
- only travel through solid
What are the features of surface waves (love and rayleigh)
- occur at lower frequency (slower)
- cause majority of damage
Love - faster, move horizontally
Rayleigh - rolling motion
- cause the most damage
What are the primary hazards of earthquakes
- ground shaking: causes buildings, bridges, roads and infrastructure to collapse
- crust fracturing: when energy released causes the
earths crust to crack
What are the secondary hazards caused by earthquakes
- soil liquefaction: violent shaking causes surface rock to loose straight and become more liquid that solid -> subsoil looses ability to support building foundations
- landslides / avalanches: ground shaking places stress on slopes so they fail
What are primary hazards of volcanoes
- lava flows: hot streams of lava up to 170 C. Slow moving so don’t threaten people
- Pyroclastic flows: mixture of hot rock, lava, ash, gas ejected at 100km/h (700C)
- Ash falls: disruptive as causes poor visibility and slippery roads causing roofs to collapse and engines to clogg
- Gas eruptions: magma contains dissolved gases (co2 / sulphur dioxide) that are released in the atmosphere and can be hazardous
What are secondary hazards of volcanoes
- Lahars: masses of rock, mud and water travel down side of volcanoes fast (cant be outrun)
- Jokulhlaup: heat of eruption can melt snow/ice in a glacier causing sudden floods which are very dangerous
