4.1 Plate Tectonics

Divergent Plate Boundary

A boundary where plates move away from each other as rising magma pushes them apart, forming new crust;

Creates mid-ocean ridges, seafloor spreading, rift valleys, and volcanoes.

Examples: Mid-Atlantic Ridge, East African Rift Valley.

Convection Cycles (Mantle Convection)

Circular movement of magma heated by Earth’s core; hot magma rises, cools near the lithosphere, spreads plates apart, and sinks again.

Creates mid-ocean ridges, volcanoes, and spreading zones.

Example: Convection beneath Mid-Atlantic Ridge.

Convergent Plate Boundary

Plates move toward each other, and one may subduct beneath the other;

creates mountains, volcanoes, island arcs, trenches, and earthquakes.

Examples: Himalayas, Andes, Mariana Trench.

Oceanic–Oceanic Subduction

Two oceanic plates collide, and the denser one subducts, causing magma to rise and form volcanic island arcs and deep trenches.

Examples: Japan, Aleutian Islands, Mariana Trench.

Oceanic–Continental Subduction

Dense oceanic crust subducts under continental crust and melts into magma that forms coastal volcanoes;

creates coastal mountains, volcanic arcs, and trenches.

Examples: Andes, Cascades, Peru-Chile Trench.

Continental–Continental Convergence

Two continental plates collide and push crust upward instead of subducting;

creates massive mountain ranges and earthquakes.

Example: Himalayas.

Transform Fault Boundary

Plates slide past each other horizontally; rough edges get stuck until stress releases suddenly as an earthquake;

creates earthquakes and linear fault zones.

Examples: San Andreas Fault, Alpine Fault.

Ring of Fire

A volcanically and seismically active zone around the Pacific Plate, driven mainly by convergent boundaries and subduction;

examples include Japan, Chile, Philippines, Alaska.

Hotspots

Areas where hot mantle plumes rise and create volcanoes independent of plate boundaries; plates move over hotspots, forming volcanic chains.

Examples: Hawaii, Yellowstone.

Transform Faults (Earthquake Zones)

Areas where plates sliding past each other repeatedly lock, build stress, and then release energy as earthquakes.

Examples: San Andreas Fault, North Anatolian Fault.