The Restless Earth

The Restless Earth

1. The Earth's surface is made of huge floating plates that are constantly moving. There are three types of plate margin.

   • Constructive plate margin
     • Constructive margins are where two plates are moving away from each other, e.g. at the mid-Atlantic ridge. Magma (molten rock) rises from the mantle to fill the gap and cools, creating new crust.
   • Conservative plate margin
     • Conservative margins are where two plates are moving sideways past each other, or are moving in the same direction but at different speeds, e.g. along the west coast of the USA.
     • Crust isn't created or destroyed.
   • Destructive plate margin
     • Where an oceanic plate meets a continental plate, the denser oceanic plate is forced down into the mantle and destroyed. This often creates volcanoes an ocean trenches (very deep sections of the ocean floor where the oceanic plate goes down).
     • Where two continental plates meet, the plates smash together, but no crust is destroyed

2. Fold Mountains

   • When tectonic plates collide the sedimentary rocks that have built up between them are folded and forced upwards to form mountains
   • So fold mountains are found at destructive plate margins and places where there used to be destructive margins e.g. the west coast of North America.
   • You get fold mountains where a continental plate and an oceanic plate collide. (e.g. the Andes in South America were formed this way).
   • You also get fold mountains where two continental plates collide. (E.g. the Himalayas in Asia were formed this way.)
   • Fold Mountain areas have lots of very high mountains, which are very rocky with steep slopes. There's often snow and glaciers in the highest bits, and lakes in the valleys between the mountains.

3. Volcanoes

   • Volcanoes are Found at Destructive and Constructive Plate Margins
     • At destructive plate margins the oceanic plate goes under the continental because it is more dense (This also creates an ocean trench.)
       • The Magma rises through the cracks in the crust called vents. The magma erupts onto the surface (where it's called lava) forming a volcano.
       • A pool of magma forms
       • The oceanic plate moves down in ]to the mantle, where it's melted and destroyed
     • At constructive margins the magma rises up into the gap created by the plates moving apart, forming a volcano
     • Some volcanoes also form part of the mantle that are really hot (called hotspot), e.g. Hawaii
   • There are Different types of Volacno
     • Composite Volcanoes (E.g. Mount Fiji in Japan) Made up of ash and lava that's erupted cooled and hardened into layers. The lava is usually thick and flows slowly. It hardens quickly to form a steep sided volcano.
     • Shield Volcanoes (E.g. Manua Loa of the Hawaiian islands) Made up of only lava. The lava is runny. It flows quickly and spreads over a wide area, forming a low, flat volcano.
   • Supervolcanoes
     • Supervolcanoes are much bigger than standard volcanoes. They develop in a handful of places around the globe - at destructive plate margins or over parts of the mantle that are really hot (called hotspots) e.g. Yellowstone National Park I the USA is on the top of the supervolcano
       • Magma rises up through cracks in the crust to form a large magma basin below to the surface. The pressure of the magma causes a circular bulge on the surface several kilometres wide.
       • The bulge eventually cracks, creating vents for lava to escape through. The lava erupts out of the vents causing earthquakes and sending up gigantic plumes of ash and rock.
       • As the magma basin erupts, the bulge is no longer supports so the it collapses - spewing up more lava.
       • The characteristics are Flat, Covers a large area and has a caldera
       • When the eruption's finished there's a big crater (called a caldera) left where the bulge collapsed. Sometimes these get filled with water to form a large lake, e.g. Lake Toba in Indonesia.
       • Fortunately there are only a few Supervolcanoes and an eruption hasn't happened for tens of thousands of years, e.g. the last one to erupt was the Lake Toba supervolcano 74,000 years ago. When there is an eruption through, it's predicted an enormous area will be affected.

4. Earthquakes

   • Earthquakes are measured in the Richter scale from 1 being very week and 10 being very destructive.