The Earths Surface
The Structure of the Earth
The Earth is made up of three different layers; the crust, the mantle and the core.
The Crust is the outside layer it is made of solid rock. The oceans and the continents lie on top of the crust.
The Mantle lies under the crust and is made of molten or semi molten rock called magma.
The Core is the center of the earth and is made of iron and nickel. It is the hottest part of the earth at around 6000C. The core can be divided into the inner core and the outer core.
Plates
The earth’s crust is broken into parts called plates. The plates with land on top are called continental plates and the plates with land on top are called oceanic plates. The lines where two plates meet is called a plate boundary.
The plates sit on top of the mantle. The magma in the mantle is moved around in a circular motion by convection currents.
Convection Currents
When magma is heated in the mantle it rises towards the crust. As it rises it cools and moves sideways. This causes friction between the magma and the crust and pulls the plates. The magma cools and sinks back down into the mantle. This process is constantly repeated.
Plate Tectonics
The study of the plates and their movements is called plate tectonics. It was originally believed that all the plates were joined together in one massive landmass called Pangea. Pangea then broke apart and the plates moved to where they are today. This is called continental drift. In the 50’s scientists discovered the Mid-Atlantic Ridge which is the boundary where the american plate is splitting from the eurasian plate.
What happens at the Plate Boundaries?
Plates Collide
Plates that collide with each other have destructive boundaries. Here the crust is destroyed. Huge pressure builds up and the heavier plate is pushed under the lighter plate. This is called Subduction. The heavier plate melts back into the mantle and the lighterplate is lifted up forming fold mountains. Plates that collide also cause earthquakes and volcanoes. The Andes are fold mountains which formed where the Nazca plate and the South American plate collide.
Plates Separate
Plates that separate from each other have constructive boundaries. Here new crust is created. Plates move apart from each other and a gap is formed. Magma rises out of the mantle to fill the gap. The magam then cools and hardens to form new crust. When this happens under water it is called sea-floor spreading. Plates that separate form volcanic mountains, volcanic islands and mid ocean ridges. Iceland is an example of a volcanic island that formed because the Eurasian Plate is seperating from the North Atlantic Plate.
Sliding Plates
Plates that slide past each other have passive boundaries. Crust is neither created or destroyed. These plates are locked together and release a huge amount of energy when they slide past each other and can cause earthquakes and fault lines. The San Andreas Fault in California is a fault line formed where the Pacific Plate is sliding past the North America Plate.
Volcanic Activity
Most volcanic activity happens around the edge of the Pacific Plate, which is why this area is known as The Pacific Ring of Fire. Volcanic activity creates mid ocean ridges, volcanic islands and volcanic mountains.
Mid Ocean Ridges
Hot molten rock known as magma rises up from the mantle through the cracks in the crust. The magma then cools and hardens and builds up forming a ridge of rock. The Mid Atlantic Ridge is being formed on the seabed between the American plates and the Eurasian and African plates.
Volcanic Islands
Mountains on the seabed formed when the magma wells up through the cracks in the crust sometimes rise above the surface of the ocean. These mountains are called volcanic islands. Iceland is an example.
Volcanic Mountains
Magma can also rise up from a magma chamber in the Earth’s crust through a vent. A vent is a narrow tube in the crust. When magma reaches the surface it is known as lava. Lava hot ash and rocks are thrown into the air as the volcano erupts and an ash cloud is formed. There is a build up of material around the vent. As more eruptions occur, layer is added to layer until a cone shaped mountain is formed. The lava continues to flow from a crater at the top of the volcano. Mount St Helens is an example of a volcanic mountain.
Types of volcano
There are three types of volcano active, dormant and extinct.
Active volcanoes erupt regularly like Mount Etna in Italy.
Dormant volcanoes have not erupted for a long time but might erupt again like Mount Vesuvius in Pompeii.
Extinct volcanoes will not erupt again like Croghan Hill in Offaly.
Socio-Economic Effects of Volcanoes
Positive Effects
The soils from lava are rich in minerals.
Tourists visit the sites of some famous volcanoes such as Mount Vesuvius.
Water heated by magma underground can be used to create geothermal energy.
Negative Effects
Gases produced by volcanoes can cause acid rain.
A lava flow bruns everything in its path.
When volcanic material mixes with water from rivers a river of mud called a lahar can formed.
Earthquakes
Earthquakes are sudden tremors or vibrations in the Earth’s Crust. When plates are pressing against each other there can be a buildup of pressure along the fault line and if the plate moves the sudden release of this energy can cause an earthquake. The point beneath the surface where the earthquake occurs is called the focus. The point on the surface directly above the earthquake is called the epicentre. The small tremors that follow an earthquake are called aftershocks.
Measuring Earthquakes
A person who studies earthquakes is called a seismologist they use instruments called seismographs to measure tremors in the earth’s crust. The Richter Scale is used to show the magnitude of an earthquake.
Damages caused by earthquakes
There is a loss of life
Buildings are damaged or collapse
Damage to electricity or gas lines can lead to fires.
How To reduce the damages caused by earthquakes
Build earthquake resistant buildings
Conduct earthquakes tsunami drills so people know what to do if one occurs.
Put early warning systems in place to alert people of the possibility of a tsunami following an earthquake.
Fold mountains
Volcanic Activity
Most volcanic activity happens around the edge of the pacific plate shich is why this area is know as the pacific ring of fire. Volcanic activity creates mid ocean ridges, volcanic islands and volcanic mountains.
Mid Ocean Ridges
Hot molten rock known as magma rises up through from the mantle through the cracks in the crust. The magma then cools hardens and builds up forming a ridge of rock. In the middle of the Atlantic the American plates are seperating from the Eurasian and African plates and is creating a mountain ridge on the sea bed known as the mid atlantic ridge.