geography 02

• There are seven major plates: Eurasian, North American, South American, African, Indo-Austratian, Pacific and Antarctic.

  There are many minor plates such as the Caribbean Juan de Fuca, Cocos, Aegean, Adriatic and Turkish.

  Volcanoes and earthquake activity often occur in similar places in narrow zones of activity.
• continental crust is very old (1500 million) and lighter compared to oceanic crust which is younger (2 million) and heavier.
• Oceanic crust is denser than continental crust because it contains more iron and magnesium minerals that make up its composition. This means that when two plates collide, the denser plate will be forced beneath the less dense plate.
• As the plates move apart very slowly magma rises from the mantle. magma erupts to the surface of the Earth. This is also accompanied by earthquakes. The magma erupts to the surface of the Earth. This is also accompanied by earthquakes. when the magma reaches the surface it cools and solidifies to form new crust of igneous rock (rock formed through cooling and solidification of magma or lava). This process is repeated many times, over a long period of time eventually forming volcanoes.
• A volcano is formed by eruptions of lava and Volcanoes are usually cone-shaped mountains or hills. When magma reaches the Earth's surface it is called lava. When lava cools, it forms rock. Volcanic eruptions can happen at convergent and divergent boundaries, but not at conservative/transform boundaries. Some volcanoes happen underwater, along the seabed or ocean floor
• The magma chamber is a collection of magma inside the Earth, below the volcano. The main vent is the main outlet for the magma to escape. Secondary vents are smaller outlets through which magma escapes. The crater is created after an eruption blows the top off the volcano. An eruption occurs when pressure in the magma chamber forces magma up the main vent, towards the crater at the do) of the volcano. Some magma will also be forced out of the secondary vents the side of the volcano.
• Volcanoes can be described in terms of activity and can be still active and erupt frequently dormant (temporarily inactive but not fully extinct)extinct (never likely to erupt again)Volcanoes can also be described by their shape or type shield or composite Shield volcanoes.