Destructive plate boundaries

Lithosphere

• the lithosphere is broken up into a number of large rigid sections called plates.

• There are 7 major plates and several minor plates.

theory of continental drift

• according to theory of continental drift, plate tectonics occur due to forceful convection currents in the earth’s mantle.

• When these plates collide Destructive plate boundaries result.

Destructive plate boundaries

• convergent boundaries -also known as

• occur when two tectonic plates collide causing one of the plates to be forced down into the mantle - subduction

• The type of crust involved can lead to different forms of volcanic activity e.g creation of mountain ranges, formation of island arcs

Volcanic Activity at Oceanic-Oceanic plate boundaries

• two oceanic plates converge, one plate subducts beneath the other and melts in the mantle - producing magma

• magma rises through the ocean floor and creates volcanic island arcs.

• E.g Japan - Pacific Plate subducts beneath the Eurasian Plate.

• The constant volcanic activity in these regions forms active volcanoes. E.g Mount Fuji in Japan.

Volcanic Activity at Oceanic-Continental Plate Boundaries

• oceanic - continental, the oceanic plate is subducted beneath the continental plate - creating magma and leading to eruptions along continental margin

• E.g The Andes mountains in South America - Oceanic Nazca plate subducts beneath the South American Plate.

• This collision formed over 200 active volcanoes along the Andes range

• These volcanoes have explosive eruptions due to high gas content and viscosity of their magma

Fold mountains at Continental-Continental Plate boundaries

• the plates collide

• The immense pressure from the collision causes the land to buckle and fold, forming mountain ranges called fold mountains.

• Most well known, Himalayays - Indian plate collides with the Eurasian plate.

• part of the alpine orogony

• E.g mount everest, the alps and the rockies products of alpine orogeny

Orogenic Events and Fold mountains over Geological Time.

• Fold mountain formation at destructive plate boundaries occured over several geological perionds

• 400 MYA caledonian orogoney: the formation of mountain ranges

• e.g Bluestack and Wicklow mountains - American and Eurasian plates collided.

• 250 MYA Armorican orogoney: the collision between African and Eurasian plates

• created ridge and valley landscape of Munster

• Macgillycuddy Reeks and the Galtees in Ireland

Summary

• destructive plate boundaries reshape the Earth’s surface.

• Oceanic - Oceanic and oceanic- continental collisions lead to volcanic activity and island arc formations.

• continental-continental collisions lead to signigiciant mountain building processes like fold mountains.

• The impact of these destructive boundaries are the Andes,the Himalayas and Volcanic island arcs like Japan