The Restless Earth
At the centre of the Earth is a ball of solid iron and nickle-called the Core.The core is split up into the Inner and Outer Core-
Around the Core is the Mantle, which is
- The inner core is the innermost hottest part, it is a primarily solid sphere about 1,216 km (760 mi) in radius. It is believed to consist of an iron-nickel alloy, and has a temperature approximately 5778 K (5505 °C).
- The outer core of the Earth is a liquid layer about 2,266 kilometers thick composed of iron and nickel which lies above the Earth's solid inner core and below its mantle. Its outer boundary lies 2,890 km (1,800 mi) beneath the Earth's surface. The transition between the inner core and outer core is located approximately 5,150 km beneath the Earth's surface.The temperature of the outer core ranges from 4400 °C in the outer regions to 6100 °C near the inner core.
semi-molten rock and very viscous.
is a between the crust and the outer core. The Earth's mantle is a rocky shell about 2,890 km (1,800 mi) thick that constitutes about 84 percent of Earth's volume. It is predominantly solid and encloses the iron-rich hot core, which occupies about 15 percent of Earth's volume. Temperatures range between 500 to 900 °C (932 to 1,652 °F) at the upper boundary with the crust; to over 4,000 °C (7,230 °F) at the boundary with the core.
comprises of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.
The Earth's Crust is split up into large plates of rock called Tectonic Plates
. The plates are made of two types of crust-1. Continetal Crust
2. Oceanic Crust
- Thicker and Less Dense than Oceanic
- Mainly made of Granite with other rocks and minerals mixed in
- Seen as the Continents we know- Mountains, Valleys, Plains.
- Very Varied
- Older than Oceanic-Most over 1,500 million years old.
- Thinner and More Dense than Continental.
- Mostly made of Basalt
- Flat ocen Planes, Trenches and Mountains, many of which are underwater volcanoes
- Younger than Continental-Most under 200 million years old
The Plates move because the mantle underneath is moving due to Convection Currents.
The Crust heats up the mantle which rises. Then it spreads sideways as it has nowhere to go. This sideways motion moves the Crust's plates. The mantles cools and sinks back down.
The places where Plates meet are called Boundaries.
Thre are Three Types of boundary-Destructive Margins
- Plates move Towards Each other
- Where an Oceanic and Continental Plate meet
- The Deser Oceanic Plate is pushed downwards and forced into the mantle where it melts
- The Continental Plate is pushed inwards so it
- Fold mountains are created
- This often creates volcanoes and ocean trenches
- Sometimes, two Continental plates meet and form fold mountains, but neither plate is forced downwards.
- Plates move away from each other
- Magma rises from the mantle to fill the gap which cools to create new crust
- Plates move sideways past each other, or in the same direction but at different speeds
- Crust isn't created or destroyed
Fold Mountains are created when Plates collide at Destructive Plate margins.
The sedimentary rock buckles and is forced upwards, creating mountains.
Fold mounains occur between two Continetnal Plates or between an Oceanic plate and a Continental plate.
Fold Mountains are very rocky with steep slopes. Snow and glaciers are often present in the highest parts. Lakes and valleys exist between the mountains.
Human Use of Fold Mountains
- High areas have thin soil due to erosion. This means Fold mountains are only really good enough for Pastoral farming (grazing animals)
- Lower areas are suitable for growing crops-steep slopes are often terraced to make growing crops easier.
- Steep-sided mountains have high lakes on them. The water is let out through pipes, and because of the steep slopes, the water falls with lots of force which drives turbines to generate electricity.
- Fold Mountains are major sources of metal ores. The steep slopes make access to the mines quite difficult for large or heavy vehicles, so roads have to be carved out of the sides of the mountain to get to the mines.
- Fold Mountain rages are a good environment to grow some types of tree, mainly coniferous trees. They're grown on the steep valley slopes and are used for things like fuel, building materials, paper and furniture.
- Fold Mountains have spectacular scenery, which attracts tourists. In the winter, people visit the mountain ranges to do certain winter sports like Skiing, Snowborading and Ice Climbing. In summer, walkers are attracted to the beautiful environment. Tunnels have been created by drilling through the middle of mountains to make straight roads which allow easier and faster transport. This also allows for better communications for tourists and people who live in the area as it is wuicker to get to places.
Case Study 1-Fold Mountains
- Located in central Europe. They strech across Austria, France, Germany, Italy, Liechtenstein, Slovenia and Switzerland.
- Formed about 30 million years ago by the collision between the African and European Plates.
- Mont Blanc is the tallest peak at 4810m on the Italian-French border.
- Around 12 million people occupy the Alps.
People use the Alps for lots of things:Farming
- The steep upland areas are used for pastoral farming to graze goats, which provide milk, chesse and meat.
- Some sunnier, South facing slopes have been terraced to plant vineyards (Lavaux, Switzerland)
- The narrow valleys are dammed to generate HEP (In the Berne area in Switzerland.)
- Switzerland gets 60% of its power from HEP in the Alps.
- The electricity produced is used locally to power homes and businesses. It's also exported to towns and cities further away.
- Salt, Iron Ore, Gold, Silver and Copper were mined in the Alps, but the mining has declined dramatically due to cheaper foreign sources.
- Scots Pine is planted all over the Alps because it's more resiliant to the goats and harsh winters, so they don't die when they are saplings. The trees are logged and sold to make things like Furniture.
- 100 million Tourists visit the Alps each year making Tourism a huge part of the economy.
- 70% of Tourists visit the steep, snow covered mountains in the winter for Skiing, Snowboarding and Ice Climbing. In the summer Tourists visit for Walking, Mountain Biking, Paragliding and Climbing.
- New Villages have been built to cater for the vast quantity of Tourists (Tignes in France)
- Ski Runs, Ski Lifts, Cable Cars, Holiday Chalets and Restaurants pepper the landscape.
People have adapted to the conditions in The Alps:
- Steep Relief: Goats are farmed there because they're well adapted to live on steep mountains. Trees and man-made defences are used to protect against Avalanches and Rock Slides.
- Poor Soils: Animals are grazed in the upper-most areas as the soil is thin and un-fertile, which means crops can't be grown very well.
- Limited Communications: Roads have been built over passes(lower points between mountains), e.g. The Mont Blanc Tunnel, which links France and Italy.It takes a long time to drive over passes and they can be blocked by snow, so tunnels have been cut through the mountains to provide fast transport links.
Here's a pretty picture of the Alps: http://www.worldatlas.com/aatlas/infopage/alps.htm
Look at the lovely scenery :)
Volcanoes are found at Destructive Plate margins and Constructive Plate margins
1. At Destructive Plate margins the Oceanic Plate goes under the Continental Plate because it is
denser(This creates and Oceanic Trench as well)
- The Oceanic Plate sinks down into the Mantle and it is destroyed by heat and fiction.
- A pool of magma forms
- The Magma rises through cracks in the crust called Vents
- Pressure builds up over time
- The Magma erupts onto the surface(where it is called Lava) forming a new Crust.
- Over time, after the Volcanoe erupts several times, the layers of Solidified Ash and Lava build up to creat a Volcano. These Volcanoes are called Composite Volcanoes (Mount Fuji in Japan)
2. At Constructive Plate margins the Magma rises up into the gap created by the Plates moving apart, this creates a volcano over time as the layers of hardened Lava build up.3. Some Volcanoes alos form over parts of the Mantle that are really hot
(called Hotspots) e.g. in Hawaii
The Three Types of Volcano
- Composite Volcanoes (Mount Fuji in Japan)
- Made up of Ash and Lava that have erupted, cooled and hardened into layers.
- The Lava ius usually thick and flows slowly(very Viscous), as it has high Silica conntent.
- It hardens quickly to form a steep-sided Volcano.
- Eruptions usually very explosive because gas builds up under pressure and then is released very suddenly and with great force.
2. Shield Volcanoes (Mauna Loa on the Hawaiian Islands)
- Made up of layers of hardened Lava.
- The Lava is runny so it flows quickly(low viscosity) as it has a low Silica content. The runny Lava spreads quickly over a wide area, forming a low, flat Volcano.
3. Dome Volcanoes (Mount Pelee in the Caribbean)
- Made up of layers of hardened Lava.
- The lava is thick and flows slowly(high viscosity) and it hardens quickly, so the Volcano is steep-sided.
We'll come on to Caldera Volcanoes(Supervolcanoes) in a mo...
A pyroclastic flow is a fast-moving current of superheated gas and rock, which can reach speeds moving away from a volcano of up to 700 km/h (450 mph) and reach temperatures of around 1,000 °C (1,830 °F). The flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. They are a common and devastating result of certain explosive volcanic eruptions.
The flow is the result of the plume losing pressure and collapsing.
Millions of people live in places near Volcanoes and are in danger of eruptions happening without much warning. With so many lives at risk it is important to try to predict eruptions, so life loss and damage to property is minimised. Scientists monitor the Volcanoes to check for tell-tale signs that an eruption is due:
- Tiny Earthquakes can be detected using Seismometers to check for vibrations in the ground.
- Escaping gases can be seen using instruments that detect Ultravioelt Radiation.
- Changes in the shape of the Volcano (bulges in the land/mountain where magma builds up under it, as seen in the 1980 eruption of Mount St. Helens)
The power of volcanic eruptions can be seen in this picture.
Before the eruption(left) and after the eruption(right) support the devastation of the eruption.
Case Study 2-Volcanoes
Montserrat, Soufriere Hills:
- Erupted June 25th 1997 (small eruptions started in July 1995)
- Large eruption-4.5 million m³ of rocks and gases released
- 19 killed
1.Montserrat is above a Destructive Plate margin, where the Atlantic Plate is being forced under the Caribbean Plate
2.Magma rose up through weak points under the Soufriere hills forming and underground pool of Magma.
3.The rock above the pool collapsed, opening a vent and causing the eruption.
Impacts and Responses
1. Primary Impacts
2. Secondary Impacts
- Large areas were covered with volcanic material-the capital city Plymouth was buried under 12m of mud and ash.
- Over 20 villages and 2/3 of homes on the island were destroyed by pyroclastic flows.
- Schools, hospitals, the airport and the port were destroyed.
- Vegetation and farmland were destroyed.
- 19 people died and 7 were injured.
3. Immediate Responses
- Fires destroyed many buildings including local Government offices, the Police HQ and the towns central petrol station.
- Tourists stayed away and businesses were destroyed, disrupting the economy.
- Population decline-8000 of the island's 12,000 inhabitants have left since the eruptions began in 1995.
- Volcanic ash from the eruption has improved soil fertility.
- Tourism on the island is now increasing as people come to see the Volcano.
4. Long-Term Responses
- People were evacuated from the South to safe areas in the North.
- Shelters were built to house evacuees.
- Temporary infrastructure was also built, e.g. roads and electricity supplies.
- The UK provided £17 million of emergency aid (Montserrat is an overseas territory of the UK)
- Local emergency services provided support units to search for and rescue survivors.
- A risk map was created and an exclusion zone is in place. Th South of the island is off-limits while the Volcano is still active.
- The UK has provided £41 million to develop the North of the island-new docks, an airport and houses have been built in the North.
- The Montserrat Volcano Observatory has been st up to try and predict future eruptions.
Supervolcanoes are much bigger than standard volcanoes. They develop in a handful of places around the World-either at Destructive Plate margins or Hotspots over the Mantle, e.g. Yellowstone National Park in the USA is on top of a Supervolcano.Here is how they form over Hotspots:
- Magma rises up through cracks in the Crust to form a large Magma Basin below the surface. The pressure of the Magma cuases a circular bulge on the surface several kilometers wide.
- The bulge eventually cracks, creating vents for Lava to escape through. The Lava erupts out of vents causing Earthquakes and sending up gigantic plumes of Ash and rock.
- As the Magma Basin empties, the bulge is no longer supported so it collapses-spweing up more Lava.
- When the eruption has finished there's a big crater called a Cladera left where the bulge collapsed. Sometimes these get filled water to form a large lake, e.g. Lake Toba in Indonesia.