Subduction — Science definition

Defined in 2 courses:

Where it is taught

In use

Continental collision commonly thickens crust and builds mountains, as in the Himalayan region; it is not the same as ordinary oceanic subduction.

Plate Boundaries

Questions using subduction

Problem 1

Which statement correctly uses subduction in Moving Plates, Boundaries & Earth Evidence?
  1. One illustrative result establishes every real condition and needs no further evidence.
  2. Every coastline is necessarily a plate boundary.
  3. A boundary map predicts the exact time of the next earthquake.
  4. subduction: One lithospheric plate sinking beneath another at a suitable convergent boundary.
Answer and explanation

subduction: One lithospheric plate sinking beneath another at a suitable convergent boundary.

One lithospheric plate sinking beneath another at a suitable convergent boundary. Separation grows by 6.0 cm in three years, a mean relative rate of 2.0 cm/year. Together with the ridge, this supports a divergent-boundary interpretation in the supplied model. It does not establish that each plate moves at exactly 2 cm/year or predict every earthquake or volcano.

Problem 2

A sinking slab changes the conditions for melting above itA sinking slab changes the conditions for melting above itOceanic plate →← upper plateCold slab descendsWater helps meltingMelting occurs mainly in overlying mantle; the slab is not a liquid belt.
This original cross-section shows an ideal oceanic subduction setting. Layer thicknesses, angles and distances are exaggerated. The rising red arrow marks a magma pathway after water-assisted mantle melting; the diagram does not locate an actual monitored volcano or predict its eruptions.
Interpret the supplied visual model. Would mountains alone uniquely identify subduction? Name a stronger evidence combination.
Answer and explanation

No. A trench, earthquake depths increasing along the descending plate and an appropriately located volcanic arc together support subduction more strongly. Continental collision can also make high mountains.

Follow the descending blue slab path, then the upward red magma pathway. These are related processes in different regions rather than one arrow tracing molten slab material.

No. A trench, earthquake depths increasing along the descending plate and an appropriately located volcanic arc together support subduction more strongly. Continental collision can also make high mountains.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 3

West and east stations on adjacent plates both move east: west 6 cm/year and east 2 cm/year in one reference frame. Find the relative closing rate. Explain why this alone does not prove a subduction zone.
Answer and explanation

The gap closes at 6−2 = 4 cm/year. Relative convergence is established, but plate types, trench geometry, earthquake depths and geological evidence are needed to distinguish subduction from other convergent settings.

The gap closes at 6−2 = 4 cm/year. Relative convergence is established, but plate types, trench geometry, earthquake depths and geological evidence are needed to distinguish subduction from other convergent settings.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

Independent chapter check: West and east stations on adjacent plates both move east: west 6 cm/year and east 2 cm/year in one reference frame. Find the relative closing rate. Explain why this alone does not prove a subduction zone.
Answer and explanation

The gap closes at 6−2 = 4 cm/year. Relative convergence is established, but plate types, trench geometry, earthquake depths and geological evidence are needed to distinguish subduction from other convergent settings.

The gap closes at 6−2 = 4 cm/year. Relative convergence is established, but plate types, trench geometry, earthquake depths and geological evidence are needed to distinguish subduction from other convergent settings.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Taught alongside

Elsewhere

Browse all courses