Geography Natural Hazards Sept 2018 Flashcards
What is a plate boundary?
where two plates meet.
What are the three types of plate boundaries?
Constructive, Destructive & Conservative
What happens at a Constructive plate boundary?
The two plates involved are moving apart at about 4-5 cm a year. As the plates move apart molten magma from the mantle escapes which over time creates a shield volcano and sometimes a volcanic island.
What is an example of a Constructive plate boundary?
The Mid-Atlantic Ridge is an example where the Eurasian plate is moving away from the North American Ridge. Iceland is an example of a volcanic island the formed here.
What happens at a Destructive plate boundary?
The two plates involved are moving together.
When an oceanic crust hits a continental crust, the heavier oceanic crust is dragged under creating a subduction zone which forms deep ocean trenches. As the magma starts to rise composite volcanoes are formed.
When two continental plates collide, the material is pushed up which form fold mountains.
What is an example of a each Destructive plate boundary?
The boundary between the Nazca plate and South American plate is an example of where a subduction zone is created. The Andes was formed by the construction of composite volcanoes.
The Himalayas are an example of fold mountains where the Indian plate collided with the Eurasian plate
What happens at a Conservative plate boundary?
The two plates involved slide past each other (in either opposite directions or the same direction at different speeds). As they move past the lock together and pressure builds up. When the pressure is released an earthquake occurs.
What is an example of a Conservative plate boundary?
The San Andreas Fault is an example where the North American plate slides past the Pacific plate on the west coast of America.
What is Pangea?
A hypothetical super continent that included all of the current land masses. This was believed to be in existence before the continents broke apart.
What is continental drift?
The gradual movement of the continents across the earth’s surface through geological time.
What is the Aesthenosphere?
The highly vicious and mechanically weak region of the upper mantle of the earth.
What is the Lithosphere?
The rigid outer most shell of the earth (the crust).
What are the qualities of an oceanic crust?
Thinner than a continental crust but denser. Can be crated and destroyed. Thickness = 7-10 km Rock type = Basalt Density = 2.9g/cm3 Alternative name = Sima
What are the qualities of a continental crust?
Thicker than an oceanic crust but less dense. A lot older than the oceanic crust. Thickness = 25-75 km Rock type = Granite Density = 2.7g/cm3 Alternative name = Sial
What is the Quaternary period?
The last 2.6 million years of earth’s life
What are the three parts of the Milankovitch cycles?
Eccentricity, Precession and Axial tilt
What is Eccentricity?
This describes the path of the Earth as it orbits the Sun. The Earth’s orbit is not fixed – it changes from being almost circular to being mildly elliptical. A complete cycle – from circular to elliptical and back to circular again – occurs about every 100000 years.
What is Precession?
This describes a natural ‘wobble’ rather like a spinning top. A complete wobble cycle takes about 26000 years. The Earth’s wobble accounts for certain regions of the world – such as the northern lights.
What is Axial tilt?
The earth spins on its axis, causing night and day. The Earth’s axis is currently tilted at an angle of 23.5 degrees. However, over a period of about 41000 years, the tilt of the Earth’s axis moves back and forth between two extremes – 21.5 degrees and 24.5 degrees.
What are sunspots?
Sunspots are black spots that can be seen on the sun. Over a period of 11 years a sunspot cycle occurs where the number of sunspots goes from a minimum to a maximum and back. When there is a maximum number of sunspots there is a higher temperature on the Earth and vice versa when there is the minimum number of sunspots.
How does the greenhouse effect work?
Short-wave radiation from the sun enters the earth’s atmosphere and some of this radiation reflects and scatters back out. Long-wave radiation is then given off by the earth. However due to the blanketing effect, CO2 and methane in the atmosphere absorb some of the radiation keeping the temperatures high.
What are the causes of the high amounts of CO2, methane and nitrous oxides in the atmosphere?
CO2 - Burning of fossil fuels, car exhausts, deforesting
and burning of wood. Global concentration
increased by 30% since 1850. Accounts for 60%
of greenhouse effect.
Methane - Burning of biomass, rice farming, farming of
livestock, decaying of organic matter.
Accounts for 20% of greenhouse effect.
Nitrous oxides - Power station, car exhausts,
agricultural fertilisers, sewage
treatment. 300x more effective at
capturing heat than CO2. Accounts for
20% of greenhouse effect.
