THE OCEAN FLOOR Formation of the Ocean Floor

THE OCEAN FLOOR

Formation of the Ocean Floor • Ocean floor formation a result of seafloor spreading • Process has been occurring for millions of years • Evidence shown in the symmetrical, parallel bands of basalt that spread out along either side of the ridge • Youngest rocks are closer to the ridge

Features of the Ocean Floor • Ocean basins have the same geological features as continents (i. e. plains, volcanic mountains, valleys) • Far more exaggerated on ocean floor • Average depth of 12, 000 feet • Formation of ocean floor features result of movement in plate tectonics

Features of the Ocean Floor • Subduction Zone – a region of the Earth’s crust where tectonic plates meet • Mountain formation and volcanic activity occur at these zones • Formation of deep ocean trenches • Result of oceanic plate sinking below continental plate

Features of the Ocean Floor • Continental Shelf – a stretch of the seabed adjacent to the shores of a particular country • Extends out under the ocean; geologically part of the continental crust • Area of shallow water known as a shelf sea • Shelves were exposed during glacial periods (15, 000 y. a. )

Features of the Ocean Floor • Continental slope – extent of ocean floor that connects continental shelf to abyssal plain • Abyssal plain – flat and gently sloping areas found at the deepest parts of the ocean • Found at depths between 10, 000 – 20, 000 ft • Covers more than 50% of Earth’s surface • Formed as a result of sediment buildup on the oceanic crust

Features of the Ocean Floor • Abyssal plains contain small hills and underwater volcanic peaks (seamounts) • Peaks of seamounts have been worn down over time to create plateau-like tops (guyots) • A chain of seamounts and volcanic islands can form island arcs • Often occur at subduction zones • Run parallel and close to a plate boundary

Sea Floor Topography • Topography: study of Earth’s surface features, on land on the ocean floor • Topographical maps show seafloor elevation and depressions • Ocean depth can be calculated automatically by sonar • Two pieces of information are needed: the speed of sound in water (1454 m/s) and time it takes for the sound signal to travel • D = 1454 x t/2; D = depth, t = time

Sea Floor Topography • Oceanographers can obtain a profile of the ocean floor by using sonar • Uses sound propagation to detect objects under the surface of water • Most modern ships are equipped with sonar • Series of events with sonar: 1. A ship’s sonar device beams a continuous sound signal downward 2. Sound reaches bottom and returns with an echo 3. Produces a line tracing of the ocean floor