1.1 Why are some locations more at risk? Flashcards
Hazard?
a geophysical event that has the potential to threaten both life and property
Convergent boundaries (destructive)?
slab pull is forcing the subduction of the oceanic plate as it is heavier and denser into Benioff zone, where friction and pressure is building up. The heat in the mantle will start to melt the end of the oceanic plate, creating more andesitic lava which is more viscous. Th VEI is higher but eruptions are less frequent. Earthquakes have a larger magnitude. If the continental plate is struggling to move forward, it will create fold mountain ranges
Conservative boundaries (transform)?
Either plates can move alongside each other, causing fault lines e.g. San Andreas fault in California, leading to large earthquakes
Hot spot?
Area where heat under the Earth’s crust is in a particular area - rising magma can produce volcanoes
Mantle?
A semi molten body of rock between the earths crust and core
Mantle plume?
Where heat rises to the surface creating basaltic volcanoes
Asthenosphere?
the lower part of the mantle
Lithosphere?
the crust and upper mantle which form plates
Subduction?
The process of one plate sinking beneath another at a convergent plate boundary along a sloping line called the Benioff zone
Intra-plate earthquake?
Occurs when there is a release in energy away from the plate boundaries. Not fully understood why it happens
What is a tsunami caused by?
an earthquake under the sea (usually greater than mag 7) or volcanic eruption, which displaces enough water to form waves
Where are tsunamis most common?
around coastlines and pacific ocean
3 things that happen as the plates move relative to each other over time?
Continents slowly drift apart
ocean basin changes in size and form
creates formations of major landforms such as mid ocean ridges and mountain chains
Describe the earths structure?
A relatively thin crust broken up into plates and wrapped around a thick and largely molten mantle
Convection?
the movement of particles through a substance, transporting their heat energy from hotter areas to cooler areas.
Heat from the core makes magma in the mantle rise towards the crust
What is believed to be the main driver of plate movement?
Convection within the mantle causing crustal plates to move
Paleomagnetism and what is it used for?
The study of prehistoric Earth’s magnetic fields recorded in rocks, sediment etc. Scientists can use this to reconstruct past plate movements.
How is new crust formed?
Sea floor spreading at divergent plate boundaries
What is slab pull?
the force created by convection currents that moves plates and drags them into subduction zones
Divergent boundaries?
moving away from each other, 2 oceanic plates due to slab pull. Basaltic magma with lower viscosity. Lower VEI but explosions are longer duration. Runnier lava.
Small earthquakes due to no friction or pressure building up as they’re rubbing together
Collision boundaries?
2 continental plates bash together e.g. eurasian plates forming fold mountains such as Himalayan mountains.
Very small chance of eruptions as the plates are moving upwards so there is very little/no magma. Earthquakes are very large and powerful
Evidence found by Wegner?
continental drift = how continents were linked together in the past, by looking at fossils of different animals in different continents and also looking at glacial evidence and the movement of glaciers e.g. erosional process and was able to notice that they have moved apart.
Paleomagnetism?
the way that the rocks were aligned in magnetic strips and as the earths magnetic core flips over long periods of time, there will flips in the rocks, which suggests the divergent plate boundaries were creating new rocks
Hazards of Earthquakes?
different types of waves (primary and secondary) which tend to move within the earths surface up from the epicentre. These are the waves that can be noticed earlier on and can give a few minutes warning before the Love waves hit, as they’re the waves that move along the surface and cause damage. This can lead to ground shaking and crustal shaking and cause aftershocks and future earthquakes
Secondary hazards due to earthquakes?
tsunamis and liquefaction (moving of the land) which can cause the water or air gaps in the rocks out. Can also cause landslides in mountain areas.
Hazards due to volcanoes?
lava which is the least damaging and dangerous as its slow moving and the most predictable. Pyroclastic flows (key reasons for death). Ash falls can cover and kill animals and crops.
hazard due to tsunamis
large water column displacement. A very large tsunami wave is caused in shallow water when the front of the water slows down and the back of the water catches up causing it to become taller. Time travel maps can provide warning of tsunamis.
