3.1.5 Processes and Associated Landforms

What is sea floor spreading?

Sea floor spreading creates oceanic crust, explained by palaeomagnetism, where lava cools and retains the magnetic polarity of Earth at the time of cooling.

What causes slow sea floor spreading?

Slow sea floor spreading occurs when the ridge is fed by small, discontinuous magma chambers.

What is subduction?

Subduction occurs when a denser plate is pushed into the upper mantle, driven by the weight of the plate, with the subducted side remaining cooler and denser than the surrounding mantle.

How does the rate of subduction relate to the rate of production?

The rate of subduction matches the rate of plate production.

What is the typical plate dip in subduction zones?

The plate dip in subduction zones ranges from 30° to 70°, with older crust having a steeper dip.

What is evidence of subduction?

Evidence of subduction includes surrounding landforms, the Beinoff zone, and disruption of temperature at depth.

What is the Beinoff Zone?

The Beinoff Zone is a narrow zone of earthquakes that dips away from the deep-sea trench and extends to 680km deep.

What causes fold mountain building in the Himalayas?

The Indo-Australian plate subducts under the Eurasian plate, causing fold mountain building with little volcanic activity.

How does fold mountain building occur in the Andes?

In the Andes, the Nazca oceanic plate subducts under the continental South American crust, with pieces of the Nazca plate becoming part of the accretionary wedge.

What causes volcanic activity in the Andes?

Partial melting of the Nazca plate produces magma, forming volcanoes in the Andes.

What are ocean ridges?

Ocean ridges occur at divergent boundaries and are a series of parallel ridges with a central double ridge separated by a ridge valley.

What happens at ocean ridges due to tension and stretching?

Tension and stretching can cause a central block to fall, contributing to the formation of ocean ridges.

What are ocean trenches?

Ocean trenches are long, narrow, asymmetric depressions in the ocean floor, found at subduction zones, with steep sides facing land masses.

Where are ocean trenches commonly located?

Ocean trenches are commonly found next to land and island arcs, particularly in the Pacific Ocean.

What are volcanic island arcs?

Volcanic island arcs are chains of volcanic islands located on the continental side of an ocean trench, formed by magma rising to the surface.

How are volcanic island arcs formed?

In volcanic island arcs, magma formed by a subducting plate rises to the surface and builds volcanoes.

What are the features of volcanic island arcs?

Features include a trench outer rise caused by the subducting plate, a gentle outer slope broken by faults, and a steep inner slope containing fragments of the subducting plate.