In the east, the indo-Australian plate is moving north and colliding against the eastern part or the Eurasian plate. As the marine sediments move upwards this then forms the Himalayas which is the highest mountain range in the world with mount Everest at its peak. Then the upwards movement is mirrored by downwards folding and folds to the mountain roots and the crust becomes deeper .
The Alps have formed because the African plate is moving north and has come into collision with the Eurasian plate. There is then a lot of pressure in the collision zone and the continental margins have moved upwards creating the Alpine Mountain range. As the uplift continues eventually the Mediterranean sea will disappear as it is getting shallower.
How they Occur? A collision margin occurs when two plates moving together are both made from continental crust. Continental crust cannot sink or be destroyed, and as a result the land between them is pushed upwards to form high ‘fold’ mountains like the Himalayas. Earthquakes are common along collision margins but there are no volcanic eruptions.