Geography+Keywords+-+A2+-+Volcanoes+-+Oxford+textbook.txt

• author "me"
• tags "Bramble1997"
• description ""
• fileName "Geography Keywords - A2 - Volcanoes - Oxford textbook"
• freezingBlueDBID -1.0
• Aftershock
• A minor earthquake or tremor following a larger and more powerful earthquake

The partial liquid layer - part of the mantle - on which the tectonic plates "float"

The zone of melting at a destructive (convergent) margin as one plate dives (subducts) beneath another

The central "core" of the Earth rich in iron and nickel compromising a solid liquid inner core (1200km thick) and a liquid outer core (2300km thick)

The outermost "skin" of the earth that varies in thickness between 12 and 120km

Mitigation approaches involving engineering solutions to reduce damage associated with ground shaking during an earthquake, such as strengthening bridge supports and the foundations of buildings

The point on the grounf surface immediately above the focus of an earthquake

Lines of weakness in the form of cracks in rocks along which relative movement (displacement) takes place. Sudden movement along faults is often associated with earthquakes

The point within the Earths crust where an earthquake originates - put simply, its the origin of an earthquake

Montain chains such as the Alps and the Andes formed by enormous compressional forces associated with a destructive (collision) plate margin

Rocks formed by the colling of a molten magma, either underground (intrusive) or on the ground surface (extrusive)

The jelly-like state of silts and clays resulting from intense ground shaking that may result in the subsidence and collapse of buildings following an earthquake

Resting on the asthenosphere, this is outermost solid layer of the Earth comprising the crust and the outer mantle. Approximately 100 km thick, it is divided into several large plates and many smaller ones

Molten rock, gases, and liquids occupying vast magma chambers at great pressure deep within the mantle. On reaching the ground surface, magma is known as lava

The concentric layer of the Earth between the crust and the outer core. The mantle is some 2870km thick

The zone of rock adjacent to an igneous body, such as a magma chamber, that has been affected (heated) by metamorphism and where rocks have changed in their mineralogy and/or texture

Deep gashes in the sea floor up to 10971m deep (the Marianas Trench) marking destructive plate margins

Rising current of heat (part of convection cells) usually associated with rising magma

The name given to the spatial pattern (ring) of volcanoes (and earthquakes) marking plate margins around the edge of the Pacific Ocean

Activity associated with the transmission of seismic (shock) waves radiating outwards from the focus of an earthquake

Instrument used to record the shockwaves (seismic waves) associated with an earthquake. Seismometers are also used to monitor earthquake in volcanic areas to help predict eruptions

A somewhat indistinct volcanic cone forming a mound up to 12m high resulting from the eruptions of "globs" of very fluid lava, typically found in Hawaii

Otherwise known as a composite volcano, a stratovolcano is made up of alternating layers of lava and ash representing a series of eruptions over many years

A crustal crack along which movement takes place in a horizontal plane (sideways) rather than vertical (up and down). Earthquakes are often associated with strike-slip faults, for example the San Andreas Fault in California, USA and the North Anatolian Fault, Turkey

Volcanoes formed beneath the sea that can either be single vent volcanoes or fissure volcanoes, where lava is emitted along a crack in the Earths crust (e.g. the Mid Atlantic Ridge)

A huge volcano that often takes the form of a caldera (collapsed volcano cone) and is associated with massive eruptions capable of having a global impact on people.Examples of supervolcanoes include Yellowstone in the USA and Taupo in New Zealand

Fragmental material emitted during a volcanic eruption, often resulting from the destruction of the volcanic cone. Tephra can vary from very fine ash to volcanic bombs (over 64mm) in size

A type of basic (rich in iron and magnesium) lava containing holes (vesicles) that represent former gas bubbles

Generic term used to describe a range of volcanic activity often associated with a place or region including volcanic eruptions, geysers and hot springs

Are forces that cause something to move away from its centre of rotation

Is the transfer of heat in a liquid or gas in a circular motion

A volcano which has not erupted within historic times is called dormant

A volcano which has not erupted for at least 10,000 years

Non governmental organisations such as the Red Cross, Oxfam and Greenpeace

As seismic waves pass through softer sediment, such as sand, the wave amplitude or height increases. This results in more intense shaking of the surface

The upper mantle and the crust make up the lithosphere

When the Earth is not in fact a perfect sphere but instead that it bulges around the equator and is flatter at the poles due to centrifugal forces

It varies from 5-10km on the oceanic crust to nearly 70km on the continental plates

Plates which are land masses

Plates which form the oceans

A shortened version for silica and magnesium which makes up the oceanic plate made from basalt

A shortened version of silica and aluminium which makes up the continental plate which is made of mainly granite rocks

An occasionally broken layer of basalt rocks known as SiMa (silica and magnesium)

Bodies of mainly granite rocks known as SiAl (because they are made up of silica and aluminium)

2900km

Due to the great heat and oressure within this zone, the mainly silicate rocks are in a thick, liquid state which becomes denser the deeper you go

4600 million years old

A layer of softer, almost plastic-like rock. The asthenosphere can move very slowly carrying the lithosphere on top.

Densities within the mantle increase as you go down into the lower mantle

The depth and hot temperature mean that we cannot drill into or physically see most of the earth. Instead, scientists map the interior by watching how seismic waves, either from earthquakes or man made blasts, travel through the various layers

Are solid and sit on top of the asthenosphere

The core

Can reach above 5000 degrees celcius

It is mostly made of iron and nickel

The core is 4 times denser than the crust

It is thought that as the Earth rotates, the liquid outer core spins, creating the earths magnetic field

150km

2250km

12000 km

The core is actually made up of two parts. The outercore is semi-liquid and consists mainly of iron. The inner core is solid and is made up of an iron-nickel alloy

Convection currents

Alfred Wegener

As far back as 1620

In 1912

Pangea

He suggested that all the present continents were originally joined together to form a single supercontinent called Pangea before drifting apart in Laurasia in the north and Gondwanaland in the South. Laurasia and Gondwanaland then broke up to form the continental arrangement we know today

• -The jigsaw fit of South America and Africa
• -Matching rock sequences (of age and type) linking northwest Scotland and eastern Canada
• -coal (formed only under warm, wet conditions) found beneath the Antarctic ice cap. Only if Antarctica was once positioned in warmer latitudes can this be explained
• -Permian fossil brachiopods in India match those in Australia
• -A unique Permian fossil reptile called mesosaurus is found only in South west Africa and Brazil
• -Glacial deposits and scratches on rocks (called strations) in Brazil match those in West Africa

In the 1950s, nuclear submarines began monitoring and mapping the ocean floors with great accuracy. The Mid-Atlantic Ridge, an underwater mountain chain, was discovered, as were similar features in the Pacific. These ridges together with deep ocean trenches were found to be seismically active - in other words, prone to earthquakes

In 1962, an American geologist named Harry Hess updated Wegeners idea. He studied the age of the rocks on the Atlantic Ocean floor, finding the youngest in the middle and oldest near the USA and the Caribbean. With the newest rocks still being formed in Iceland, this was compelling evidence that the Atlantic sea floor was spreading outwards from centre, a concept known as sea floor spreading.

Around 5cm a year - as fast as your finger nails

The idea that the sea floor is speading outwards from the centre

Every 400,000 years or so