Hazards full Flashcards
what is a hazard?
it is a potential threat to human life and property. it can either be hydro-meteorological or geophysical
what are hydro-meteorological hazards?
caused by climatic processes
what are geophysical hazards?
caused by land processes
where do geophysical hazards occur?
they occur near plate boundaries. these plates moved different speeds and directions which can cause collisions, earthquakes and volcanic activity.
where do earthquakes mainly take place?
greatest in the Pacific Ocean along the ring of fire. also the entire ocean is ringed by areas known as subduction zones.
other than near plate boundaries where else can earthquakes occur?
near the middle of plates (called an intra-plate). this is when pre-existing weaknesses become reactivated, forming seismic waves. for example, an intraplate earthquake may occur if solid crust, which has weakened over time, cracks under pressure
explain volcanic hotspots
- these occur ‘intra-plate’ meaning amongst the centre of plates
- this occurs when a localised area of the lithosphere (earth’s crust and upper mantle) has an unusually high temp due to the upwelling of hot molten material from the core. this was first theorised by Tuzo Wilson in 1963.
- This produces isolated plumes of convecting heat, called mantle plumes, which rise towards the surface, generating basaltic volcanoes that tend to erupt continuously.
- This over time can produce a chain of volcanic islands.
e.g. Kilauea, Hawaii
where do the most powerful earthquakes generally happen?
at convergent or conservative boundaries
what is the OFZ (oceanic fracture zone)?
this is a belt of activity through the oceans and along the mid-ocean ridges through Africa, the Red Sea and the Dead Sea
what is the CFZ (continental fracture zone)?
this is a belt of activity along the mountain ranges from Spain through the alps to the Middle East and to the Himalayas
what are the tectonic trends since 1960?
- the total number of recorded hazards, one of the main reasons for this is due to CC and global warming.
- the number of fatalities has decreased due to the increased protection and preparation
- the total number of people being affected by tectonic hazards is increasing, due to pop growth, increased density has increased vulnerability
- the economic costs associated with hazards and disasters has increased significantly. this is partly due to increases in development as infrastructure in more developed countries costs more to repair. increasing number of insurance policies, especially in developed countries, heightens the costs.
why is reporting disaster impacts (e.g. fatalities) very difficult and controversial?
- depends on whether you look at the direct deaths so those killed straight away or indirectly by looking at how many people died of diseases that spread after the disaster
- the location is important as rural and isolated areas are hard to reach and so it may be hard to collect data from them.
also areas of high pop densities may be hard to collect from - the number of deaths quoted by a government may be subject to bias. in the 2004 tsunami, the Burmese government claimed there were 0 deaths in Burma. this may be to try and show the government is doing a good job.
what are the four sections of the earth?
crust
mantle
outer core
inner core
what is the crust like?
also known as the lithosphere. the uppermost layer of the earth which is thinnest, least dense and lightest. oceanic crust is only 7km thick, whereas continental crust can be up to 70km thick
what is the mantle like?
may also be called the asthenosphere. widest layer. the mantle is semi-molten and a temperature gradient towards the core generates convection currents. this may contribute to the lithosphere’s plate tectonic movement. the mantle is at a depth from 700km to 2890km below the crust.
what is the outer core like?
dense, semi-molten rocks containing iron and nickel alloys. at a depth of 2890km to 5150km below the earth’s surface. temps of 4500-6000ºC
what is the inner core like?
similar composition to the outer core. its over 5150km below the earth’s crust. the inner core is solid iron due to the extreme pressures it experiences. temperature of over 5000ºC. the core’s high temperature is a result of:
- radiogenic heat produced form radioactive decay
- primordial heat left over from the earth’s formation
what is the lithosphere?
consists of the crust and the rigid upper section of the mantle and is approximately 80-90km thick. this is the section of the earth that is divided into seven very large plates and a number of smaller ones. the plates are divided into oceanic and continental plates.
what is the asthenosphere?
this lies beneath the lithosphere and is semi-molten on which the plates float and move
what causes tectonic plates to move?
radioactive reactions occur inside the core which produces convection currents in the mantle. this causes the tectonic plates to move. The friction between the convection current and the crust causes the tectonic plate to move.
where are volcanoes predominately located?
along the ring of fire which borders the indo-australian plate to the south west, the Eurasian plate to the north west and the North American plate to the west
- they are usually found at plate boundaries where plates converge or diverge, anomalies include hotspots.
what was wegner’s continental drift theory?
- in 1912 he published his theory that a single continent that he called Pangea, existed about 300 million years ago
- he states that the shapes of South America and Africa seem to fit together so were once part of a supercontinent
- he suggested mountains formed when the edge of a drifting continent collided with another causing the floor to crumble and fold
- took 150 years to be accepted as scientists still believed mountains are causing by cooling of the earth as well as it being difficult to find viable evidence
what are examples of Wegner’s continental drift theory?
- similar fossils found where these plates could have fit, but are now separated by oceans. remains of the reptile Mesosaurus found in both South America and southern africa. it is unlikely that the reptile could have developed over both areas or migrated across the Atlantic
- rock sequences in northern Scotland closely agree with those found in eastern Canada, indicating that they were laid down under the same conditions in one location
- land masses fit like a jigsaw
other than Wegner what is another piece of evidence for continental drift theory?
how seismic waves travel through the earth. along the wadati-benioff foci, the depth of waves shows subdiction of the denser basaltic oceanic plates into the upper mantle.