Landforms Associated with P

At what type of plate boundary(ies) would you find ocean ridges?

O&O constructive

Outline processes involved in the formation of ocean ridges. (4 marks)

• Ocean ridges are formed at constructive plate boundaries (two oceanic crusts).

• Convection currents operating in the mantle act like a conveyor belt driving movement of the lithosphere above (the plates move away from each other).

• When the plates pull apart due to ridge push, basaltic lava flows to the surface.

• Overtime, solidified, hardened lava forms underwater mountain ranges.

• NAME AN EXAMPLE

Name an example of an ocean ridge

The Mid Atlantic Ridge in the Atlantic Ocean

At what type of plate boundary(ies) would you find ocean trenches?

O&O and O&C destructive

How are ocean trenches formed?

• Ocean trenches, the deepest parts of the ocean, are formed by a process called subduction at destrucitve plate boundaries (oceanic vs oceanic or oceanic vs continental)

• When two tectonic plates collide, the denser plate is forced beneath the other, leading to a bend in the seafloor and the creation of a deep, V-shaped depression called a trench

Name an example of an ocean trench

The Mariana Trench

At what type of plate boundary(ies) would you find rift valleys?

O&O constructive

How are rift valleys formed?

• Rift valleys form when the Earth's crust is stretched and thinned, eventually pulling apart along fault lines

• This process, known as rifting, occurs at constructive plate boundaries where tectonic plates move away from each other

• The resulting depression is a rift valley, often characterised by steep sides and a flat floor

Name an example of a rift valley

Þingvellir (Thingvellir), Iceland

At what type of plate boundary(ies) would you find fold mountains?

O&C and C&C destructive/collision

What are the 2 types of fold?

Syncline and anticline

Syncline

Where rocks are folded downwards (down folds)

Syncline = sink

Anticline

Areas where rocks are folded upwards (up folds)

How are fold mountains formed?

• Rivers erode material from the land and transport it to the sea

• Sediment is deposited on the ocean floor with layers building up over time forming sedimentary rock

• Plates move together at destructive/collision boundaries, and rocks crumple

• As a result, the plates buckle upwards and are folded, creating mountains with anticlines and synclines

Name an example of a fold mountain range

Himalayas, Alps, Andes

At what type of plate boundary(ies) would you find island arcs?

O&O destructive

How are island arcs formed?

• During subduction at a destructive plate boundary, the descending plate melts in the Benioff zone

• The melted material is also lighter and more gassy than the material already in the mantle, so it rises towards the surface, through the crust as plutons of magma

• Eventually, these reach the surface as explosive volcanoes

• When these occur offshore, a line of volcanoes may form called island arcs

Name an example of an island arc

The Mariana Islands