A Science Odyssey Mountain Maker, Earth Shaker

The Sea Floor Spread

Map that shows the Earth's divergent margins, all connected

The Earth's longest mountain chain isn't the Andes in South America, or the Himalayas in Asia, or even North America's Rockies. It's an underwater chain of mountains 47,000 miles long. The chain runs down the middle of the Atlantic Ocean (surfacing at Iceland), around Africa, through the Indian Ocean, between Australia and Antarctica, and north through the Pacific Ocean.

Running along the top of this chain of mountains is a deep crack, called a rift valley. It is here that new ocean floor is continuously created.

Gif Animation, endless loop: wide view of divergent margin, show magama filling gap made my the two separating plates.

As the two sides of the mountain move away from each other, magma wells up from the Earth's interior. It then solidifies into rock as it is cooled by the sea, creating new ocean floor.

The speed at which new ocean floor is created varies from one location on the ocean ridge to another. Between North America and Europe, the rate is about 2.2 inches (3.6 cm) per year. At the East Pacific rise, which is pushing a plate into the west coast of South America, the rate is 12.6 inches (32.2 cm) per year.

The Continental Slide (convergent boundary)

The Continental Crush (collisional 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