Under the Sea Chapter 4

Bathymetry Discovery & study of the ocean floor History: Improvements: throw heavy rope tied to a rock over the side of the boat measured fathoms as arm lengths Improvements: Echo Sounding, Multi-beam Systems & Satellite Systems

Echo Soundings After Titanic (1912) & WWI increase in bathymetry. Why? Looked for better way to study ocean Developed a sound pulse and listen for echo Similar to dolphins, porpoises, & ocras which use echolocation

Echo Sounding Problems ship position not certain speed of sound varies with temp, pressure, salinity and affects readings images were fuzzy

Multi-beam Systems 121 beams from ship to take echo sounding more accurate reading Like “mowing the lawn” gave a section to interpret rather than a single point

Satellite Altimetry Satellites measure small variations in the elevation of surface water Many radar pulses each second Used sophisticated calculations to determine the sea floor

Topography of Ocean Floors Seabed topography is due to isostatic equilibrium Balancing of less dense continental plate and more dense oceanic plate over mantle Submerged outer edge of continent = continental margin Deep sea floor = ocean basin

Continental Margins Active Margins: Passive Margins: continental margins of converging plates Lots of volcanic & earthquake activity Ex: Pacific Plate Passive Margins: continental margins of diverging plates Little volcanic & earthquake activity Ex: Mid-Atlantic Ridge

3 types of Continental Margins Continental Shelf Continental Slope Continental Rise

Continental Shelf Shallow submerged extension of continent Features: hills, depressions, sedimentary rocks, & mineral/oil deposits Gentle incline Consists of material from erosion (ex: river mouths) which can determine the width of shelf Affected by sea level: ice age can change isostatic equilibrium Used for resources: minerals & oil

Continental Slope Transition between the continental shelf & the ocean floor Sediments from shelf are transported over the side creating a slope Often scraped off by subduction Shelf break = abrupt transition from continental shelf to the continental slope

Submarine Canyons Canyons cut into shelf & slope Fan-shaped Usually right angle to shoreline Formed from erosion and/or earthquakes Earthquakes create turbidity currents (avalanche of sediment)

Continental Rise Sediment at base of slope transported from shelf Deep-ocean currents &/ turbidity currents

Deep-Ocean Basins Oceanic ridge systems and adjacent sediment-covered plains Includes: Oceanic Ridges Hydrothermal Vents Abyssal Plains & Abyssal Hills Seamounts & Guyots Trenches & Island Arcs

Oceanic Ridges Mountainous chain of basaltic rock at center of spreading center Formed from divergent boundaries Old rocks far away from center Young rocks at center Not in straight line, broken up by transform faults and fracture zones (remnants of transform faults)

Hydrothermal Vents Hot springs from ridge floor Forms from water into cracks of ridge floor and venting out Water is hot, acidic, filled with minerals, and gases Unusual organisms live here

Abyssal Plains & Abyssal Plains flat sediment covered floor found on periphery of all oceans Sediment from turbidity currents or winds Hills: small volcanoes, from diverent boundaries, parallel / borders ridges

Seamounts & Guyots Formed from old hotspots Seamounts: Guyot: old volcanoes never breeched surface Guyot: former islands eroded down Ex: 100+ small islands of Hawaii

Trenches & Island Arcs Trenches: Island Arcs: Deep depression in ocean floor Deepest part of ocean Forms from subduction zones Island Arcs: chain of volcanic islands from subduction zones Ex: Aleutian Islands