The Restless Earth
The Earth's plates are frequently colliding with each other. The collision of the Earth's plates leads to intense pressure along their zones of contact. The pressure from plate collisions causes the rock layers of the crust to fold. When rock layers buckle(=bend and give way under a weight or force) this forces them upwards to create fold mountain chains. When one plate is forced under another plate it sinks down into the intensely hot mantle (=the layer of hot rocks between the crust and the core) and melts. Melted rock is lighter than solid rock, so some of it will rise upwards to the surface through the buckled and folded rock layers. The melted rock wells up to erupt violently at the surface, creating some of the most dangerous volcanoes on Earth. An example of such an eruption was at Mount StHelens in the Rocky Mountains in 1980 which killed 57 people.
Several terms to know: Earthquakes occur where plates collide or slide past each other and compression and cracking of rock causes shock waves to spread from the focus. When these waves reach the surface, the ground trembles, causing great damage to life and property. The phenomenon of folding can occur where plate boundaries collide and compression causes parts of the Earth's crust to become raised and buckled into mountains. Volcanic mountains are formed where plates collide and magma reaches the surface violently through a vent. Layers of ash and lava gradually form a volcanic cone, which will have a crater at its summit. Mid ocean ridges can be formed where plate boundaries separate beneath the oceans. Magma makes its way to the surface along long cracks to form raised formations. Some higher parts may protrude above the surface of the ocean in the form of volcanic islands. Plates are the layers on the surface of the Earth's crust which make up our continents and the floors of our oceans. The Pacific Ring of Fire is the world's largest earthquake and volcanic zone. The process of continental drift by which convection currents in the mantle below the Earth's surface cause the plates to move slowly and also cause the boundaries of plates to collide with and separate from each other.