plate tectonics
How tectonic plates move
Plates diverge, converge and slide past one another along narrow boundary zones. Each style of boundary leaves a distinctive signature: new ocean floor, deep trenches and volcanic arcs, or long transform faults like the San Andreas.
About: Plate tectonics · Pacific Plate · Mid-Atlantic Ridge · San Andreas Fault · Subduction
Four kinds of boundary
Most plate movement is concentrated along narrow zones between plates, at four types of boundary: divergent, convergent, transform, and broader plate-boundary zones where deformation spreads across a wide belt.[1]
Where plates pull apart
At divergent boundaries, new crust is created as plates separate. Along the Mid-Atlantic Ridge the spreading rate averages about 2.5 centimetres a year — roughly 25 kilometres every million years.[1]
In East Africa, the same family of processes is at work within a continent. If spreading there continues, the rift region may one day flood and East Africa may become the site of the Earth’s next major ocean — an inference about the geological future, and labelled as such.[1]
Where plates collide
At convergent boundaries crust is destroyed: one plate sinks beneath another at a subduction zone, and subduction carves the deepest parts of the ocean floor.[1]
The Challenger Deep, at the southern end of the Mariana Trench, plunges nearly 11,000 metres below sea level — deeper than Mount Everest is tall.[1]
When two continents meet, neither will subduct. The collision of India into Asia, beginning about 50 million years ago, crumpled the crust upward into the Himalaya and the Tibetan Plateau — a process that continues today.[1,2]
Where plates slide past each other
At transform boundaries, crust is neither created nor destroyed. The San Andreas fault zone — about 1,300 kilometres long — carries the Pacific Plate past the North American Plate at an average of about 5 centimetres a year, the Pacific side moving northwest relative to the North American side.[1,2,3]
What drives it all
For decades the driving force was attributed chiefly to mantle convection and the push of magma at spreading ridges. Since the 1990s the weight of opinion has shifted to slab pull: the gravity-driven sinking of cold, dense oceanic slabs dragging their plates behind them. Lithoen records this as an inference — the prevailing interpretation, not a settled measurement.[1,2]
Bracketed references link to the structured entity records whose claims support each paragraph. Last updated 2026-09-06.