A Science Odyssey Mountain Maker, Earth Shaker

The Continental Crush

GIF Animation, endless loop: side view of collisional margin

An ocean floor pushed toward a land mass will always slide under the land mass. This is because the land mass is more buoyant, or lighter, than the ocean floor. When two land masses meet, on the other hand, neither will slide under the other. Instead, the two crush together at what is known as a collisional boundary. They crumple and fold. Some pieces of land are thrust over or under other pieces. The result is a mountain range.

The Himalayas, the highest mountains in the world, were created this way. (In fact, they're still growing.) So were the European Alps. Even the Appalachian Mountains formed when two land masses came together. Although with the Appalachians, the crushing ended long ago -- all that's left now are the eroded remnants of a once high mountain range.

The Sea Floor Spread (divergent boundary)

The Continental Slide (convergent boundary)

Slippin' and a Slidin' (transform boundary)

Back to first page of Plate Tectonics

Home | You Try It Menu | People and Discoveries | Printable Version | Help

WGBH | PBS Online | Search | Feedback | Shop
© 1998 WGBH