Formation of Destructive plate boundaries

The earth's crust is broken into plates that move around the mantle. The edges of the plates are called boundaries; they mark the point where plates meet. At destructive plate boundaries, two plates collide and land is destroyed. Different plate boundaries exist as plate boundaries move by convection currents.

At continental-continental destructive plate boundaries, fold mountains are formed, e.g. the Himalayas, where the Indian and Eurasian plates slowly collided over millions of years. Continental crust is 40-60km thick, made of sial-rich rock, and is older than oceanic crust. The Eurasian plate crumpled and rose to form the Tibetan Plateau and the Himalayas. When 2 continental plates collide, neither sinks; they squeeze together and are compressed, then buckle upwards and the pressure creates shallow earthquakes. For example, in Pakistan in 2005, a shallow earthquake occurred and 89,000 people died. Fold mountains are usually made from sedimentary rock as they form underwater. Marine fossils are found in the Himalayas because the rock was underwater before it was uplifted by plate movement.7

Oceanic-continental destructive boundaries 

Oceanic plates are heavier than continental plates so when they collide, the heavier oceanic plate subducts under the lighter continental plate. 2 SRPs As it moves downwards it melts, turns to magma and moves up through the continental crust, causing an explosive volcano to form, e.g. Mount Saint Helens, USA. 2 SRPs Deep earthquakes are also common at these boundaries because the plate movement is not smooth and they can sometimes get stuck. When they suddenly start moving again the pressure is released as an earthquake. 2 SRPs A trench is created at the junction of two colliding plates. This marks the subduction zone, e.g. Peru-Chile Trench. 2 SRPs The Pacific Ring of Fire is an area that contains 452 active volcanoes at the subduction zone at the edge of the Pacific Plate. 75% of the world’s active volcanoes are here, e.g. Mount Pinatubo and Mount Fuji, Japan. 2 SRPs At the point of collision, the continental plate buckles upwards and fold mountains are formed, e.g. the Andes formed due to the collision between the Nazca plate and the South American plate. 2 SRPs 

At a boundary where two oceanic plates collide, the heaviest one subducts beneath the lighter one and a deep ocean trench forms, like the Mariana Trench in the Pacific ocean. This trench marks where the Pacific plate subducts under the Philippine plate. SRPs - surplus Strong earthquakes can occur at trenches to release pressure, e.g. Japan 2011. They lead to Tsunamis as they happen under the sea. SRPs - surplus The subducted plate sinks and melts, causing raising plumes of magma to break through the crust, creating active volcanoes under the sea. SRPs - surplus The material from the volcanoes builds upon the sea floor until it is visible on the surface to form an island arc, e.g. the Philippine Islands. SRPs - surplus An island arc is a curved line of volcanic islands marking a subduction zone; they are parallel to the ocean trench.