Processes & Landforms Along Plate Boundaries

Plate Boundaries Overview

  • Three main types: Convergent, Divergent, Transform Fault (Strike-Slip).

  • Movements drive geologic processes and create distinctive landforms.

Convergent Boundaries

Oceanic–Continental

  • Motion: Dense oceanic plate →\rightarrow subducts beneath lighter continental plate.

  • Processes: subduction, melting of slab edge, magma rise, mantle plume, powerful earthquakes, potential tsunamis.

  • Landforms: trench (at contact), continental volcanic arc (parallel chain of volcanoes) on overriding plate.

Oceanic–Oceanic

  • Motion: Older/denser oceanic plate subducts under the other.

  • Processes: subduction, magma generation, frequent earthquakes, tsunamis from seafloor displacement.

  • Landforms: trench; volcanic island arc (string of oceanic volcanoes).

Continental–Continental

  • Motion: Two buoyant continental plates collide; neither can sink.

  • Processes: intense compression, shallow earthquakes, large-scale faulting; no subduction or volcanism.

  • Landforms: very high mountain ranges (e.g., Himalayas), broad collision zone.

Divergent Boundaries

  • Motion: Plates pull apart.

  • Processes: tension creates rift; mantle material rises, cools, solidifies →\rightarrow new crust; shallow quakes; continuous seafloor spreading.

  • Landforms: rift valley (initial split), mid-ocean/oceanic ridge (underwater mountain chain), widening basin with new seafloor.

Transform Fault Boundaries

  • Motion: Plates slide horizontally past each other.

  • Processes: rock breakage along fault, sudden release of strain →\rightarrow strong earthquakes; movement is mostly horizontal, so no subduction, volcanism, or major vertical displacement.

  • Landforms: long linear faults (e.g., San Andreas Fault); offset streams, roads, ridges.

Key Processes

  • Subduction: dense plate sinks into mantle; triggers melting, volcanism, trenches.

  • Seafloor Spreading: magma fills gap at divergent boundary, forms new oceanic crust.

  • Earthquakes: rapid energy release from plate motion; strongest at convergent & transform margins.

  • Tsunamis: large seafloor displacement (usually at convergent boundaries) sends water waves landward.

Key Landforms at a Glance

  • Trench – deep oceanic depression at subduction zones.

  • Volcanic Arc – continental volcano chain above subducting slab.

  • Volcanic Island Arc – oceanic volcano chain above subducting oceanic plate.

  • Mountain Range – folded/thickened crust at continental collision.

  • Rift Valley – down-faulted block where lithosphere splits.

  • Oceanic Ridge – continuous submarine mountain system at divergence.

  • Fault – fracture/zone of fractures where rocks slide past (transform or within collision zones).

Quick Recall Points

  1. Density controls subduction: denser plate always descends.

  2. No volcanoes without subduction: continental–continental & pure transform faults lack active volcanism.

  3. Divergence builds crust; convergence destroys/recycles crust.

  4. Earthquake focus depth: shallow at divergence & transform; deep quakes restricted to subduction zones.

  5. Tsunamis require vertical water displacement—predominant at convergent margins.