Theme C - The Restless Earth Flashcards
How is metamorphic rock formed?
Metamorphic rock is other rocks which were changed by heat or pressure.
E.g limestone under pressure turns to marble
Mudstone heated turns to slate
How is sedimentary rock formed?
Small particles of rock or dead animals are deposited under the sea and deposited as sediment which builds up in layers. They get squeezed and turned into rock.
Limestone is made from Dead Sea creatures
Sandstone is made from sand particles
State the characteristics of common rock types
- Basalt - dark grey/black, glittery specks
- Granite - speckled grey, white, black, pink, very hard, large crystals visible
- Limestone - grey, white or yellow, may have fossils, fizzes when drop of acid is added
- Sandstone - yellow/orange, often see grains of sand, may rub off
- Slate - dark grey, layers split easily, smooth, can be marked
- Marble - White, swirls of colour, can be highly polished for floors or fireplaces.
What are tectonic plates
The segments that make up the earths crust are known as tectonic plates which float on the semi-liquid mantle below. On average plates move 7cm a year.
The intensely hot core heats the mantle and this causes convection currents. As the currents reach the top of the mantle and spread out they drag the plates slowly apart.
When convection currents cool and sink back towards the core they drag plates above them closer together.
For the destructive plate boundary explain;
- plate movement
- Explanation of name
- processes
- features
- Destructive
Plate movement - plates come together
Exp of name - crust is destroyed
Processes - when plates meet the oceanic plate is forced to bend and go down into the mantle beneath the continental plate. This is the process of subduction and it triggers earthquakes as the plate bends. Friction and the heat of the mantle melt the descending plate forming magma which rises and forms volcanoes on the continental plate.
Features - earthquakes, volcanoes, fold mountains and an oceanic trench
For the constructive plate boundary explain;
- plate movement
- Explanation of name
- processes
- features
Plate movement - plates move apart
Exp of name - new crust formed or constructed
Processes - as the two plates move apart magma rises from the mantle to fill the gap forming new crust
Features - earthquakes, volcanoes and mid-ocean ridge
For the conservative plate boundary explain;
- plate movement
- Explanation of name
- processes
- features
Plate movement - plates slide past each other
Exp of name - crust is conserved - neither destroyed or added
Processes - two plates slide past each other along a fault line. Friction between them means they tend to stick until pressure builds up and is released in sudden jerking movement ; an earthquake
Features - earthquakes but no volcanoes
What is a collision zone?
When two continental plates meet there is a head on collision. India was separated from the rest of Asia by the sea. The Indo-Australian plate crashed into the Eurasian plate the sediments on the sea floor between India and Asia were folded and lifted upwards making fold mountains called the Himalayas.
- sometimes magma start to rise through fold mountains but cools before it reaches the surface forming intrusive igneous rock.
- earthquake activity common as there’s so much rock movement
What and how is a lava plateau formed?
A large upland flat area made when runny lava erupts from cracks called fissures and flows a long way before cooling.
- it spreads out fills in dips and made a flat surface
- several eruptions happen over a long period giving layers of basalt on top of each other
E.g Antrim plateau
What and how is a basalt column formed?
Tall thin blocks of basalt
- some are hexagonal but not all. Usually when basalt cools it cools quickly
- if lava fills a dip in the ground it makes a deep pool and cools more slowly than usual. As it cools lava shrinks and pulls inward making cracks these are the edges of the basalt columns.
E.g giants causeway
What is a volcanic plug and how is it formed?
Hills which rise steeply from surrounding land
- made when magma in a volcano cooled down inside the vent and turned to rock called dolerite. This is harder than the surrounding rock so it is left sticking up when other rock is worn away
E.g Slemish mountain, co. Antrim
What is an earthquake and how is it measured
An earthquake is a shock or wave of shocks caused by a sudden earth movement
- the focus is the point in the earths crust where the earthquake occurs
- the epicentre is the point on the earths surface directly above where it’s effects are first felt
- seismograph is the instrument that records shock waves and the Richter scale measures the magnitude of the earthquake
Name and explain the two physical consequences of earthquakes
- Liquefaction - happens when rock or soil containing water is shaken by an earthquake. Water rises to the surface and turns soil to liquid mud. Any buildings resting on this sink into the mud and collapse
- A tsunami - a large wave of seawater caused by an earthquake under the sea. Shock waves from the plate movement create small waves (30cm high) on the ocean surface, as they move upward to shore and come into shallower water they become much larger - (up to 30m high)
How is igneous rock formed?
- If magma is cooled above ground it is called lava and cools quickly making tiny crystals. This is extrusive igneous rock. E.g Basalt
- If magma cools underground if cools slowly making large crystals, this is known as intrusive igneous rock. E.g granite.
