rift

A linear zone where the earth's crust is being pulled apart — a tear in the planet's surface, widening slowly over millions of years. Where rifting succeeds, continents split and new ocean basins form: the Red Sea is a young rift that has filled with water, and the East African Rift is an active tear that will eventually split the continent. Where rifting fails, it leaves behind a sunken valley called an aulacogen — a scar from a wound that didn't open all the way.