Global Hazards Flashcards
What is the crust?
The crust is the outer layer of the Earth which humans reside. It is the thinnest and most dense layer. It varies from 5-70km in depth.
What is the mantle?
The mantle is the thickest section of the Earth at approximately 2,900 km. The mantle is made up of semi-molten rock called magma.
What is the inner core?
The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C.
What is the outer core?
The outer core is the layer surrounding the inner core of the earth. It is a liquid layer, also made up of iron and nickel. It is still extremely hot, with temperatures similar to the inner core.
What are convection currents?
Convection currents are caused by the heat from the core which heats the mantle, this rising heat goes two separate ways in the mantle (left and right) this causes plates to move.
What is slab pull?
Slab pull occurs where older, denser oceanic plates sink into the mantle at subduction zones. As these older sections of plates sink, newer and less dense sections of plate are pulled along behind. Sinking in one place leads to plates moving apart in other places.
What is a destructive plate boundary?
A destructive plate margin
usually involves an oceanic plate and a continental plate. The plates move towards one another and this movement can cause earthquakes. As the plates collide, the oceanic plate is forced beneath the continental plate. This is known as
subduction. This happens because the oceanic plate is denser (heavier) than the continental plate. This can form volcanos.
If two continental plates collide, neither can sink and so the land buckles upwards to form fold mountains. This is called a
collision boundary. Earthquakes can occur at collision boundaries.
What is a conservative plate boundary?
At a conservative plate margin, the plates move past each other or are side by side moving at different speeds. As the plates move, friction occurs and plates become stuck. Pressure builds up because the plates are still trying to move. When the pressure is released, it sends out huge amounts of energy, causing an earthquake.
What is a constructive plate boundary?
At a constructive plate margin the plates move apart from one another. When this happens the magma from the mantle rises up to construct new land in the form of a shield volcano. The movement of the plates over the mantle can cause earthquakes.
What is a shallow focus earthquake?
Shallow-focus earthquakes are the most common type, accounting for about 75% of all seismic activity. These earthquakes occur at depths less than 70 kilometres below the Earth’s surface. Shallow focus earthquakes don’t take much time for the energy to get to the epicentre so they can be very destructive.
What is a deep-focus earthquake
Deep-focus earthquakes are much rarer than shallow-focus. They are also rarely destructive because it takes a lot longer for the energy to reach the epicentre.
How are shield volcanoes formed? What are they like?
Formed at constructive plate boundaries, they are formed by eruptions of thin, runny lava.
Gentle volcano, magma rises and sets to create a dome shaped volcano. It has thin runny lava, frequent but relatively gentle eruptions
How are composite volcanoes formed? What are they like?
They occur on destructive plate boundaries
Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just consist of lava).
The partially melted mantle that rises up is viscous, it contains trapped seawater and hot gasses. This builds up pressure, when it is released, steam and dangerous gasses erupt violently.
The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow. A pyroclastic flow is a mixture of hot steam, ash, rock and dust.
A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400°C.
What is a hotspot?
Hotspots are places where large plumes of magma rise up through the crust. They are caused by a static source of magma, often away from plate margins. As the plate moves away from the hotspot, a new volcano island will form.
Explain the causes of an eruption you have studied (Eyjafjallajökull)
Eyjafjallajökull is on a constructive plate boundary between two oceanic plates; the North-American plate and the Eurasian plate forming the Mid-Atlantic Ridge. This weakness in the crust causes volcanoes to be present
Iceland is also on a hotspot. This means that there is increased volcanic activity.
What were the local impacts of the Eyjafjallajökull eruption?
Visibility in the local, rural area, was extremely poor and people had to wear goggles and facemasks. Over 500 farmers and their families had to be evacuated as the roads surrounding the volcano were shut down.
The ash contaminated local water supplies causing farmers to have to bring their livestock indoors.
Finally large floods of water (called jökulhlaups) swept down the side of the volcano destroying bridges and roads.
What were the international consequences of the Eyjafjallajökull eruption?
During the eruption there was an 8 day travel ban across much of Eastern/Northern Europe. Around 107,000 flights accounting for 48% of total air traffic and roughly 10 million passengers.
Airlines lost an estimated £1.2bn as they could not fly due to the ash in the atmosphere.
Further to this food supplies that were normally flown to locations could not be transported. 20% of the Kenyan economy is based on the export of vegetables and cut flowers to Europe. Over 50,000 farmers were temporarily unemployed as their produce could not be sold.
Explain how areas of low pressure form climate zones; particularly the ITCZ
The ITCZ is a zone of convergence at the equator where the trade winds meet. It is a low pressure belt and migrates with the changing position of the equator. Variation in the location of the ITCZ dramatically affects rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics.
Explain how areas of high pressure create climate zones (deserts and polar environments)
The air travels in the upper atmosphere and sinks at approximately 30° north and 30° south of the Equator (this is where the majority of deserts are found) where the Hadley and Ferrel cells meet. When the air sinks it creates an area of high pressure. These high-pressure areas experience very dry and warm conditions resulting in a hot desert climate. This creates a belt of desert regions
Why do we have weather extremes?
- Latitude and High Pressure zones
- Rain Shadow
A rain shadow is a patch of land that has been forced to become a desert because mountain ranges blocked all plant-growing, rainy weather. On one side of the mountain, wet weather systems drop rain and snow. On the other side of the mountain—the rain shadow side—all that precipitation is blocked. - Monsoon
A monsoon climate is characterised by a dramatic seasonal change in direction of the prevailing winds of a region which brings a marked change in rainfall.
What happens during El Nino?
During El Nino, the trade winds weaken, stop or even reverse in the Western Pacific.
The piled up warmer water around Australia makes its way back eastwards across the Pacific, leading to a 30cm rise in sea level around Peru preventing the usual cold upwelling.
As a result there is more warm water over the coast of Peru leading to rising air and low pressure. The water becomes 6-8c warmer in the eastern Pacific.
Peru would therefore experience more rainfall than normal.
In Australasia, however, the water becomes cooler and there is less air rising resulting in high pressure and stable, dry conditions.
What happens during La Nina?
La Nina event may, but does not always, follow an El Nino event. La Nina refers to unusually cold sea temperatures (3-5c colder) found in the Eastern Tropical Pacific. Broadly speaking, the impacts of La Nina are the opposite of El Nino, where Australia would experience droughts during El Nino, there could be increased risk of flooding during La Nina. Likewise, Peru could experience droughts during La Nina. La Nina could also be described as a more exaggerated version of a normal year in the Pacific Ocean. El Nino and La Nina are among the most powerful phenomena on Earth, affecting climate across more than half of the planet. Their consequences can, in fact, be global.
Explain how the global circulation of the atmosphere causes extremes in weather conditions in different parts of the world
Point: The global circulation of the atmosphere, driven by uneven heating of the Earth’s surface, plays a crucial role in causing extremes in weather conditions worldwide.
Evidence: At the equator, solar radiation is more intense, leading to warm air rising and creating a low-pressure zone. As the air rises, it cools and condenses, resulting in heavy rainfall and the formation of the Intertropical Convergence Zone (ITCZ). Conversely, at the poles, solar radiation is less intense, causing colder temperatures and high-pressure systems. The temperature contrast between the equator and the poles drives the movement of air masses, creating global wind patterns such as the trade winds, westerlies, and polar easterlies.
Explain: These global wind patterns play a key role in transporting heat and moisture across different regions, thereby influencing weather conditions. For instance, regions near the equator experience consistently warm and wet conditions due to the convergence of air masses and high levels of precipitation associated with the ITCZ. Conversely, areas situated under the descending limbs of the Hadley, Ferrel, and Polar cells, such as deserts and subtropical regions, often experience dry and arid conditions due to descending air, which inhibits cloud formation and precipitation.
Link: Therefore, the global circulation of the atmosphere creates a dynamic system of air movement that leads to variations in weather conditions worldwide.
Describe the distribution and the frequency of drought.
Areas most at risk from drought are central and southern Africa, the Middle East, Australia, eastern South America and parts of North America. The distribution of droughts has changed over time. Since 1950, there have been more droughts in Africa, Asia and the Mediterranean and fewer droughts in the Americas and Russia. The frequency of droughts however, has not altered much in that same time period. Some scientists predict that droughts might become more frequent and more severe in the future due to climate change.
