1. Classification of Ocean Floor Deep Ocean Basins

2. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Features of the deep ocean floor:  Oceanic Ridges  Hydrothermal Vents  Trenches  Island Arcs  Abyssal Plains  Abyssal Hills  Seamounts  Volcanic Islands  Guyots Deep-Ocean Basins

3. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. An oceanic ridge is a mountainous chain of young, basaltic rock at an active spreading center of an ocean. Long, underwater mountain ranges. The largest tectonic feature on the earth. More than 1500 km wide, 64,000 km (40,000 miles) long. Rises 2-3 km (up to 2 mi) high above the abyssal plain. Has a central rift valley. Composed of basalt rocks. Faulted with strike-slip (transform) faults. Shallow earthquakes occur along central rift. Deep-Ocean Basins

4. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Deep-Ocean Basins

5. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Hydrothermal vents are sites where superheated water containing dissolved minerals and gases escapes through fissures or vents. Usually associated with mid-ocean ridges Deep-Ocean Basins

6. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Deep-Ocean Basins

7. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Trenches are long, narrow, deep depressions in the ocean floor with steep sides caused by the subduction of a converging ocean plate. Trenches are the deepest places on Earth. Deep-Ocean Basins

8. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Island Arcs, chains of volcanic islands and seamounts, are usually found parallel to the edges of ocean trenches Found along ocean-ocean convergent boundaries Deep-Ocean Basins As two oceanic plates converge, an island arc is formed by volcanic activity.

9. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Abyssal Plain -Very flat area of the ocean floor at the edge of the continental rise. Average depth is about 4-6 km (2.5-4 mi). Covered by a layer of sediment, mostly <1 km thick. The flattest areas on the planet. Deep-Ocean Basins

10. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Abyssal hills are small, extinct volcanoes or rock intrusions found between the continental margins and oceanic ridges. Deep-Ocean Basins

11. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Seamounts are volcanic projections from the ocean floor that do not rise above sea level (underwater volcanoes). Associated with hot spots and mid-ocean ridges If seamounts break the surface of the ocean, they create volcanic islands The biggest mountain on earth is Mauna Loa (Hawaii). Deep-Ocean Basins

12. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Over time, wave & wind action erodes the peak of a seamount or volcanic island to form a flat-topped tablemount or guyot. Guyots were once volcanic peaks above sea level. They were eroded by wave action as they sank beneath the surface of the water. As seamount or guyot is being eroded, it is also being moved away from the ridge or hotspot. Hot Spots: Surface expression of plumes of magma rising from a stationary source of heat in the mantle. Deep-Ocean Basins

14. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. A volcanic island chain can form when a plate passes over a hot spot.

15. Hawaiian Islands-Emperor Seamount Chain A hotspot in the middle of the Pacific plate creates a volcano. Pacific Plate is moving northwest. As the plate moves, a new island forms & is active. Result: a chain of extinct volcanoes that is progressively older away from the hotspot

16. Over time… There is a “bend” in the HI island chain: 1. The Pacific Plate used to move north and changed directions to move northwestward OR 2. the hotspot could have changed locations. In the future, the HI island chain will subduct into the Aleutian Trench as new islands form. There is a new island about 1 km below the surface called Loihi.

17. Coral Reef Development Darwin noticed on his voyage on the HMS Beagle that coral reefs developed around sinking volcanic islands. Corals form in shallow, warm, tropical seawater. Temperature, salinity, and turbidity of the water have to be just right. The coral polyp (animal) secretes limestone, which serves as the skeleton that new polyps grow on to build the coral reef.

18. Fringing Reef Corals develop around a landmass. If it’s on a hotspot (active volcano), lava can destroy corals. When the volcano becomes inactive and subsides, corals develop toward barrier stage. Moorea, French Polynesia

19. Barrier Reef When the island subsides, or sea level rises, corals will continue to build upward and form a circular reef. Water in between the reef and island/land is called the lagoon. If land subsides or sea level rises faster than the coral can grow, than it will die off. Great Barrier Reef, Australia

20. Atoll When the island is completely submerged and conditions are right for the coral, all that will be visible on the surface is the coral reef. If enough coral debris builds up, a narrow island can be large enough to allow habitation. Tuanake, French Polynesia

21. © 2002 Brooks/Cole, a division of Thomson Learning, Inc. A pie chart showing the distribution of Earth’s solid surface.