risk of tectonic hazards Flashcards
what is a hazard
a potential threat to human life and property
where do earthquakes occur?
earthquakes occur along all plate boundaries and also near the middle of plates (intra -plate earthquakes)
what are intra-plate earthquakes?
they occur near the middle of plates and are usually associated with MAJOR ancient fault lines being re-activated by tectonic stress
- e.g. New Madrid seismic zone on the Mississippi river generates up to magnitude 7.5
they can also occur due to stress/pressure on the earth
- e.g. pressure on the earth from a dam in South-West China in 2008 caused an earthquake killing 90,000 people.
where do volcanoes occur?
they occur along DIVERGENT (creates SHIELD VOLCANOES) and CONVERGENT (creates STRATOVOLCANOES) plate boundaries and also due to hotspots
how are hot-spot volcanoes formed?
1) a mantle plume develops and the heat causes mantle material to rise
2) when the mantle plume reaches the base of the LITHOSPHERE, the reduction is pressure causes the mantle rock to melt and the magma rises through the cracks
what is the difference between continental and oceanic hotspots?
continental hotspots occur beneath the CONTINTENTAL CRUST and produce stratovolcanoes
- Yellowstone (VEI =8)
oceanic hotspots occur beneath oceanic crust and produces shield volcanoes
- Hawaiian islands (VEI=1)
how are tsunamis formed?
caused by tectonic activity
- earthquake causes a column of water to shift, causing a domino effect.
caused by landslides due to earthquakes and volcanic eruptions
caused by underwater volcanic eruption.
where do tsunamis take place?
they mostly occur at convergent boundaries and 70% occur around the PACIFIC
what are the three main layers of the earth?
the crust
the mantle
the core
what are the two types of crust?
CONTINENTAL - thicker but less dense - GRANITE
OCEANIC - thinner but denser - BASALT
what are the layers in the mantle?
the UPPER MANTLE
- the lithosphere (rigid layer)
- the asthenosphere (semi-molten, moves under high pressure)
the LOWER MANTLE
what makes up the core?
the INNER CORE - solid centre
the OUTER CORE - semi-molten
what is convection?
the heat from decay in the core moves upwards into the mantle and creates CONVECTION CURRENTS which push up into the spreading mid-ocean ridges and force them apart (ridge push)
what is seafloor spreading?
lava cools and solidifies with the minerals lining up with the magnetic field
- palaeomagnetism provides evidence that the sea floor has gradually moves apart
what is slab pull?
1) convection currents in the mantle drag the overlying lithosphere TOWARDS each other
2) when the two plates meet, the denser plate (oceanic) subducts beneath the less dense plate (continental)
3) as the denser crust cools, it becomes denser and gravity forces the lithosphere down into the subduction zone
4) as it sinks it pulls the plate with it (slab PULL)
what occurs at the convergent boundary with a continental and oceanic?
the plates move TOWARDS EACH OTHER
- oceanic plate subducts beneath continental
forms sea trenches, VIOLENT volcanoes and earthquakes
what occurs at the convergent boundary with two oceanic?
the heavier of the two plates subducts, forming trenches and SUBMARINE volcanic eruptions
what occurs at a constructive plate boundary?
the plates are MOVING APART (MID-ATLANTIC RIDGE)
- both earthquakes and volcanoes
what occurs at collision plate boundaries?
two plates of similar density move TOWARDS EACH OTHER forcing each other upwards as neither can subduct
- earthquakes
what are P waves?
P waves are the primary waves from earthquakes:
- quickest
- travel through both solids and liquids
- backwards and forwards shaking
- least damaging
What are S waves?
they are the secondary waves from earthquakes:
- slower than P waves
- only travel through solids
- cause an up and down motion
- more damaging
what are primary hazards of an earthquake?
these are those that are a direct result of the earthquake such as:
- ground shaking
- crustal fracturing - the earth’s crust cracks
what are secondary hazards?
these are a result of the primary hazards, such as:
- landslides and avalanches - the movement of the earth may trigger the collapse of material
- liquefaction - causing the ground to move further apart and act like a liquid
- flooding - caused by tsunami
what are primary hazards of a volcano?
those that are a direct result of the eruption, such as
- pyroclastic flow - a mix of hot and dense, rock, ash and gases
- lava flow
- ash falls
- gas eruptions
