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

• also known as convergent boundaries - have a major impact on earth’s landscape and geological activity.

• These boundaries occur when two tectonic plates collide causing one of the plates to be forced down into the mantle, this process is subduction.

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

Volcanic Activity at Oceanic-Oceanic plate boundaries

• when two oceanic plates converge, one plate subducts beneath the other and melts as it goes in the mantle.

• The melting produces magma, which rises through the ocean floor and creates volcanic island arcs.

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

• This subduction process results in active volcanic islands and steep, central- vent volcanoes - steep slopes and narrow base

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

Volcanic Activity at Oceanic-Continental Plate Boundaries

• When an oceanic plate collides with a continental plate, the denser oceanic plate is subducted beneath the lighter continental plate.

• This process creates magma, leading to volcanic eruptions along the 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, Mt Aconcagua and Mt Llullaillaco.

• These volcanoes have explosive eruptions due to high gas content and viscosity of their magma forming steep layered structures,

Fold mountains at Continental-Continental Plate boundaries

• destructive plate boundaries involving two continental plates.

• 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.

• This process is part of the Alpine Orogoney took place 30 MYA and continues to uplift the Himalayas creating high peaks, e,g Mount Everest.

• The Alps in Europe and the Rockies in North America are products of the Alpine orogony.

Orogenic Events and Fold mountains over Geological Time.

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

• The caledonian orogoney about 400 MYA led to the formation of mountain ranges e.g Bluestack and Wicklow mountains in Ireland - where the American and Eurasian plates collided.

• The Armorican orogoney took place 250 MYA involves the collision between the African and Eurasian plates and created ridge and valley landscape of Munster - Macgillycuddy Reeks and the Galtees in Ireland

Summary

• destructive plate boundaries are powerful tectonic zones that 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 convergent boundaries is evident in landscapes such as the Andes,the Himalayas and Volcanic island arcs like Japan