Slab pull and ridge push
Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Beyond NCERT
Meaning
Slab pull and ridge push are two forces that most scientists today think drive plate motion. This topic is beyond NCERT.
- Slab pull: at a subduction zone, the cold, heavy edge of a plate sinks into the mantle and drags the rest of the plate behind it. It is thought to be the largest force.
- Ridge push: new crust at a mid-ocean ridge is hot and raised up. Under gravity, it slides down and away from the ridge and pushes the plate along. This force is smaller.
Example
The Pacific plate is one of the fastest-moving plates. It has long sinking edges at trenches like the Mariana Trench, so slab pull is strong. Plates with long subduction edges tend to move faster.
Don't confuse with
- Convection currents (Holmes): the older idea that loops of hot mantle drag the plates from below. Slab pull and ridge push are forces from the plates themselves, through their weight and height.
- Pole-fleeing and tidal forces: these were Wegener's forces, and scholars found them too weak to move continents.