Chapter 6 - Managing natural hazards Flashcards
What is a natural hazard?
A natural hazard is a naturally occurring event that will have a negative impact on people.
What is a natural disaster?
A natural disaster is when a natural hazard causes damage and the people affected are unable to cope.
Diagram of the earths inner structure
Describe the characteristics of the inner core
Inner core has a temperature of 5000-6000 degrees Celsius, is solid due to the intense pressure from overlying rocks and is made from iron and nickel.
Describe the characteristics of the outer core
Outer core has a temperature of 4000-5000oC, is liquid and is make from iron and nickel.
Describe the characteristics of the mantle
Mantle has a temperature of 1000-1200oC, is liquid and flows slowly due to the convectional currents from the core and is made of mainly silicate minerals.
Describe the characteristics of the oceanic crust
Oceanic crust is made from silicate and magnesium minerals, mainly made form basalt, thin at a depth of 6km, denser at 3g cm-3, younger and can sink and is continually being renewed and destroyed.
Describe the characteristics of the continental crust
Continental crust is made from silicate and aluminium minerals, mainly made from granite, thick at a depth of 35km but can be up to 100km under mountain ranges, lighter as 2.6g cm-3, older and cannot sink and is neither destroyed nor renewed.
What is a tectonic plate?
Tectonic plate is a piece of lithosphere that moves slowly. It is made of crust and upper mantle.
What is the relation between convection currents and tectonic plates?
Where the convection currents rise to the surface, the plates move away from each other and where the convection currents sink, plates move towards each other.
What is a plate boundary?
Plate boundary is where two or more plates meet, the three main types of plate boundaries are constructive, destructive and conservative.
What are constructive (divergent) plate boundaries?
Constructive (divergent) plate boundaries are when two oceanic plates are pulling away from each other. A gap or weakness is formed and magma from the mantle rises to the surface due to convection currents. The magma solidifies when contact is made with the cold ocean water. The magma turns to lava and forms a new basaltic ocean crust. This process is called seafloor spreading or ridge push, this triggers a small earthquake. The new ocean crust builds up to form mid ocean ridges and can also form submarine volcanoes, which may grow an appear above sea level as volcanic islands. These volcanoes are called shield or basic volcanoes and usually have non-explosive eruptions because there is little pressure build up. An example of this type of plate boundary is where the Eurasian plate moves away from the north American plate along the mid-Atlantic ridge.
What forms if continental plates move away from each other?
If two continental plates move away from each other, a rift valley may form as the central block of land drops down between the faults.
What are destructive (convergent) plate boundaries?
Destructive (convergent) plate boundaries are when two plates move towards each other. This can occur between two oceanic plates, two continental plates or an oceanic plate and a continental plate. When an oceanic plate and continental plate move towards each other, the denser oceanic plate is forced down (subduction) under the lighter continental plate. This happens in the subduction zone and an ocean trench is formed. There trenches are the deepest parts of the ocean. The friction between the plate triggers earthquakes and the heat produced due to friction turns the descending plate into magma. The magma starts to rise and erupt due to pressure through a weakness in the crust as an explosive composite volcano. Fold mountains also formed. The magma that erupts at the surface forms a chain of volcanic islands called as island arc. If two continental plates move towards each other, the sediments between the two plates are compressed (collision zone) and pushed upwards to form fold mountains.
What are fold mountains?
Fold mountains are mountains created where two or more tectonic plates are pushed together, compressing the rocks and folding them upwards.
What are conservative plate boundaries?
Conservative plate boundaries occur when two plates slide past each other. They move at different speeds. The plates get locked together and pressure builds up until it is released as an earthquake.
What is magnitude?
Magnitude measures the strength of an earthquake. It is measured om the Richter scale.
What are volcanoes?
Volcanoes are caused due to tectonic activity. They are found on constructive and destructive plate boundaries.
What is the focus of an earthquake?
Focus is where the earthquake begins underground.
What is the epicentre of an earthquake?
Epicentre is the point on the surface above the focus.
What is a seismometer?
Seismometer is an instrument used to measure the magnitude of an earthquake on the Richter scale.
What are the nine factors affecting the impact of an earthquake?
location of the epicentre, time of the earthquake, geology of the area, relief of the area, severity of aftershocks, level of development of human settlement, population density, building density and building strength.
What are the four conditions required for a tropical cyclone to form?
Tropical cyclones need to have ocean surface temperatures of at least 27oC, ocean depth of at least 60 meters, very little shear wind and these conditions must occur between 5o and 20o north or south of the equator to form.
Why do tropical cyclones need warm oceans to form?
The warm ocean water provides the energy to evaporate more water that rises, and condenses, releasing huge amounts of energy.
Why do tropical cyclones only form between 5 and 20 degrees north or south of the equator?
The 5o and 20o north or south of the equator mean that there is an optimal amount of Coriolis force (rotation of the earth) to make the air spin fast enough.
why do tropical cyclones need little shear wind to form?
The little change in wind speed or direction prevents the stoppage of the vertical development.
When do tropical cyclones form and what direction do they spin?
They form between May and November in the northern hemisphere and spin clockwise. They form between November and May in the southern hemisphere and spin anticlockwise.
What is flooding?
Flooding is when the discharge of a river exceeds the capacity of the rivers channel. When this occurs, the river overflows the banks and covers the adjacent floodplain.
What are the eleven causes of flooding?
weather, previous weather, soil and rock type, relief, earthquakes/volcanoes/tropical cyclones, deforestation, urbanisation, agriculture and climate change
How does weather cause flooding?
heavy intense rainfall can exceed the infiltration capacity of the soil and lead to an increase in overland flow. Steady prolonged rainfall can saturate the soil and caused the water table to rise, reducing infiltration capacity. Overland flow will occur if snow melt is rapid and the ground beneath frozen.
How does previous weather cause flooding?
Antecedent soil moisture refers to the amount of water in the soil before a rainfall event. The more saturated the soil, the less infiltration and the more overland flow.
How does soil and rock type cause flooding?
Impermeable soils and rocks, such as clay or granite, have a low infiltration capacity and percolation rate, which leads to greater overland flow.
How does relief cause flooding?
Steeper gradients can lead to faster overland flow and water has little time to infiltrate.
How do earthquakes, volcanoes and tropical cyclones cause flooding?
These natural hazards can produce tsunamis and storm surges that flood low-lying coastal areas.
How does deforestation cause flooding?
Cutting down trees reduces interception and infiltration.
How does urbanisation cause flooding?
Concrete and tarmac are impermeable surfaces that lead to more overland flow. Store drains speed up the movement of water to the nearest river.
How does agriculture cause flooding?
Overgrazing and leaving soil expose reduces interception. Ploughing down rather than across lopes quickly channels the water downwards. Heavy farm machinery compacts the soil, making it impermeable.
How does climate change cause flooding?
Enhanced global warming may lead to a rise in sea levels, as well as more rainfall and storms in certain parts of the world.
What is drought?
Drought is when there is a lack of rain or less rain than normal over a long period of time.
How is drought caused and provide an example
Changes in atmospheric circulation patterns altering storm tracks and wind patterns. An example of this is patterns that prevent the northwards movement of the inter tropical convergence zone into the Sahel region of Africa, which means that the moist rising air at the inter tropical convergence zone does not move north to reach Sahel.
How can droughts occur?
Air in a high-pressure system sinks and rain clouds generally do not form. If the sinking air covers a large area than normal or becomes prolonged, droughts can occur
How does El Niño cause droughts?
The El Niño southern oscillation is a weather event where the surface water in the Pacific Ocean along south America rises in temperature. These warmer waters change circulation patters and alter storm patters and can cause droughts in Australia.