Quick questions on Plate boundaries and processes - WJEC A-Level Geology

Plates interact in three ways. At a constructive (divergent) boundary plates move apart and new crust is created. At a destructive (convergent) boundary plates move together and crust is destroyed by subduction or crumpled in collision. At a conservative (transform) boundary plates slide past one another and crust is neither created nor destroyed.

Plates slide horizontally past one another along a transform fault. No crust is created or destroyed and there is no volcanism, but stress builds and releases in powerful, shallow earthquakes (the San Andreas Fault, California).

Three forces move the plates. Mantle convection drags the base of the plates. Ridge push arises because new, hot, high-standing crust at a ridge slides down and pushes the plate away. Slab pull, now regarded as the dominant force, is the pull of the dense, cold subducting slab sinking into the mantle and dragging the plate behind it.

A constructive margin running the length of the Atlantic, building new basaltic crust and surfacing in Iceland, with a rift valley and shallow earthquakes. The Andes. An oceanic-continental destructive margin where the Nazca plate subducts beneath South America, producing a trench, explosive volcanoes and fold mountains. The San Andreas Fault. A conservative margin where the Pacific and North American plates slide past one another, generating major Californian earthquakes but no volcanoes.

State what is created or destroyed at each of the three boundary types. [3 marks]

Name the inclined zone of deep earthquakes at a subduction zone. [1 mark]

Identify the driving force now regarded as most important, and explain it. [2 marks]