Rates of plate movement
Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Class 11, Ch 4 "Distribution of Oceans and Continents"
Meaning
Plates move very slowly, usually a few centimetres a year. Scientists first measured these speeds from the magnetic stripes, which are bands of rock on the ocean floor running parallel to the ridges. Each stripe records a known period of time, so its width shows how fast the floor spread. Today, GPS measures plate motion directly. Speeds vary a lot:
- Slowest: the Arctic Ridge, under 2.5 cm a year
- Fastest: the East Pacific Rise near Easter Island, about 3,400 km west of Chile, over 15 cm a year
Example
The Indian plate moves north-northeast at about 4-5 cm a year, slower than hair grows. Before it hit Asia, it moved unusually fast, at up to about 15-20 cm a year.
Don't confuse with
- Rate of Himalayan uplift: the Himalayas rise about 5 mm a year, which is the growth in height of the mountains. India's plate moves about 5 cm a year, which is the horizontal movement of the plate. They are ten times apart.