OCEAN BOTTOM FEATURES

TOPOGRAPHIC FEATURES u u Continental margins: * Shelf up to 300 km wide; m deep * Slope km wide; 200 to 2000 m deep (Often furrowed by canyons); Slopes 1 in 40. * Rise up to 300 km wide; 2000 to 5000 m deep (Slopes 1 in 700 to 1 in 1000) * Trench 600 to 11,000 m deep

TOPOGRAPHIC FEATURES u u There are 26 trenches in the world ocean:   3 in the Atlantic Ocean   1 in the Indian Ocean   22 in the Pacific Ocean u u Deep sea basins about 5000 m deep u u Abyssal Plains are extremely flat, sediment-filled u u Abyssal Hills rise from the plains up to 1000 m u u Mid-ocean ridge: Interconnected mountain system up to 400 km wide Rises to m u u Central rift valley km wide cuts m deep into the ridge system

OCEAN BOTTOM FEATURES u u Seamounts & Trenches. Trenches are found adjacent & parallel to continents & island chains.

u u Depths of major trenches exceed 18,000 feet. u u The deepest is the Marianas Trench, 35,810 ft.

u u The continental slope gradually rises from the abyssal plains & climbs as much as 45 deg as it approaches land. u u In some areas the slope is interrupted by broad wedges of sediment deposits called a continental rise.

u u The continental shelf, the region from the coastline to the edge of the continental slope, covers about 8 % of the global seafloor area. u u Average width is 40 miles.

u u Seamounts are isolated mountains rising from 3,000 to 10,000 feet above the surrounding seabed.

u u A beach is an expanse of sand or pebbles along a seashore, that is washed by the tide & waves. u u Three zones: Offshore, foreshore and back shore.

u u Summer time residents of each zone usually include surfers, waders, & sun bathers. u u The offshore zone has incoming waves that feel bottom and curl over as breakers or surf.

u u Foreshore zone is regularly exposed to high & low tides. u u On the landward edge of the foreshore is the beach scarp, usually a rise of several feet caused by the eroding action of stronger waves.

u u The Backshore zone extends from the water line to the inland area where the sea does not influence vegetation. u u The principal feature of the backshore is the berm that marks the ordinary limit of a high tide.

u u Most beach sand consists of light-colored quartz and feldspar sand grains, the result of weathering and erosion of rocks such as granite.

u u Some beach sand comes directly from shoreline erosion, but much is created by the action of rivers flowing to the sea.

u u Tropical beaches often consist entirely of shell and coral fragments. u u Beaches in areas of volcanic activity can be black, its sand created by erosion of volcanic rock.