Sea Floor Spreading and the Marianas

What is sea floor spreading?

-the process by which new seafloor is formed as it moves away from spreading centers in mid-ocean ridges.

What are some of the major land forms that are created from plate movement?

-mountains, rift valleys, volcanoes, and ocean trenches.

How were the Mariana Islands formed?

-they were formed by underwater volcanoes along the Marianas Trench.

What evidence exists today that the plates are still moving and that the islands are ancient volcanoes?

-recent volcanic activities, and earthquakes.

What is an atoll?

-a coral reef that develops as a ring around a central lagoon.

Why are atolls mainly found on the Pacific?

-because the Pacific Ocean floor has the most volcanic activities; thus the pacific has many coral reefs.

Critical Thinking!

Why are most oceanic trenches found in the Pacific Ocean?

features of the Pacific-its floor, islands, and coasts--can be explained by the theory of continental drift. This theory says that the crust of the Earth is divided into thin, rigid plates that are moving. New crustal material is formed along these ridges by volcanic action. As this new material is added it pushes the plates apart and causes their motion. As the ocean plates are pushed toward the continental plates from the mid-ocean ridges, they are pushed below the continental plates into the Earth's interior. As they descend, oceanic trenches are formed. These are relatively narrow, linear, and very deep valleys that lie parallel to the continental coasts. The Pacific has the greatest number of these trenches. Underneath most of the Pacific Ocean is the very large Pacific Plate. In the eastern Pacific, off Central America, is the small Cocos Plate, and west of South America is the Nazca Plate. The Philippine Sea Plate is east of the islands of the same name, and the Eurasian Plate underlies the seas west of the islands of East Asia. The floor of the Pacific is divided into two parts each roughly half of the floor but each is very different from the other. The eastern half has few mountains or ridges, and therefore few islands, but the western half has many of both. The eastern part, but not the western, is crossed by many cracks arranged in bands called fracture zones that run parallel to each other--mostly at right angles to the coasts of the Americas.

Fish of the Marianas