Glossary for Restless Earth Flashcards
Crust
The outer layer of the earth.
Plate
A section of the earth’s crust.
Mantle
The dense, mostly solid layer between the outer core and the crust.
Convection currents
The circular currents of heat in the mantle.
Inner core
The centre and hottest part of the earth. It’s solid and made up of iron and nickel. Temperatures up to 5500oC.
Outer core
Surrounds the inner core. A liquid layer, also make up of iron and nickle.
Oceanic crust
Newer, most less than 200 million years old. Denser than continental crust. Can be subducted (sink). Can be renewed and destroyed.
Continental crust
Older, most over 1500 million years old. Less dense than oceanic crust. Cannot be subducted (sink). Cannot be renewed and destroyed.
Plate margins
The boundary where two plates meet.
Subduction
When a oceanic plate sinks below a continental plate.
Destructive - subduction
Oceanic plate moves into and subducts beneath continental plate. E.g. Juan de Fuca Plate (oceanic) subducts beneath North American Plate (continental).
Destructive - collision
Two continental plates move together to form fold mountains. E.g. Indo-Australian Plate (continental) collides with the Eurasian Plate (continental) to form the Himalayas.
Constructive
Two plates move away from one another. If two oceanic plates move apart shield volcanoes form to create islands. E.g. North American Plate and the Eurasian Plate move away to form the Mid-Atlantic ridge and Iceland.
Conservative
Two plates slide past one another, getting locked together and often jolting past each other to form earthquakes. Volcanoes do not form at this margin. E.g. North American Plate and the Pacific Plate create the San Andreas Fault - a conservative fault line under San Francisco.
Young fold mountains
Large mountain ranges where rock layers have been crumpled and forced upwards as they have been forced together at destructive margins.
Geosynclines
Huge valleys where sediments are deposited by rivers and the sea. Layers of rock build up in geosynclines and it is these layers that are forced upwards to form young fold mountains.
The Alps, Europe
Europe’s highest young fold mountain range.
Transhumance
The seasonal movement of livestock up and down the mountains. Livestock is taken up the mountain in the summer months to graze on the pasture in the high valleys, and then brought back down into the valley floor during the winter months.
HEP
Hydro-electric power. Dams and reservoirs are often built in mountainous areas because the valleys are steep and narrow.
Ski Industry
Skiing is not the biggest economic wealth creator in the Alps. Its worth 100s of millions to businesses in the Alps.
Multiplier effect
As one business grows in an area (skiing) so do other businesses that are connected to it (e.g. equipment hire shops, restaurants, camping sites etc).
Mining
The Alps have been folded out of the crust - with the mountains metals, minerals and fossil fuels have been forced out of the crust too. These now lie relatively close to the surface and can be mined easily.
Livigno, Italy - a community who have adapted to life in the high Alps
Invested heavily in the ski industry - farmland has been reverted to ski slopes (farm diversification).
Developed infrastructure and communications - tunnels, motorways, cable cars, ski lifts. Roads are built with snow sheds and hairpins - a highly sinuous road - they are built to reduce gradient/steepness of roads.
Transhumance has stopped in favour of valley farming and valley living - urban areas built in sheltered valleys.
Ocean trenches
Deep sections of the ocean, usually where an oceanic plate is sinking below a continental plate. Mariana Trench, in the Pacific, is the deepest part of the planet where two oceanic plates are being subducted.
Composite volcanoes
A steep sided volcano that is made up of a variety of materials such as lava and ash. The lava is viscous (sticky) which helps create the steep sides. Eruptions can be pyroclastic. E.g. Mt St Helens, Cascade Ridge, USA.
Shield volcanoes
A broad, gently sloping volcano that is composed of lava. The lava is non-visous (not sticky) which means that sides are gentle. E.g. Mauna Loa, Hawaii.
Natural hazard
An occurrence over which people have little control, which poses a threat to people’s lives and possessions.
Vent
The opening - usually central and single - in a volcano from which magma is erupted.
Magma
Molten rock found within the earth’s crust.
Lava
Magma that has come out of the crust through a vent and been oxidised (mixed with air).
Pyroclastic flow
The build up of pressure under a lava dome can turn lava, ash and dust into a gaseous mix. When the lava dome erupts this then moves rapidly through the air and down the volcano side at 200mph. Temperature is over 200oC.
Lava dome
The plug at the top of a volcano - that traps lava beneath. Lava domes are deformed days before eruption.
Crater
The large open-faced area around the vent at the top of a volcano.
Lahar
A secondary effect that is basically a volcanic mudflow. Ash mixes with rainwater or snowmelt to form huge flows of mud (e.g. Mt St Helens, USA 1980).
