Download Features of the Ocean Floor (1).

What were some of the
important findings from the
HMS Challenger
 Major findings included:
 First plot of currents and temperatures in oceans
 Map of ocean sediments
 Outline of main contours of ocean basins
 Discovery of mid-atlantic ridge (baffled them)
 Mariana Trench measured at 26,000 feet. Deepest point
in ocean.
 4,717 new ocean life forms discovered.
 Discovery of life at depths greater than 18,000 feet.
 Three major zones
 Continental margins
 The ocean basin floor
 The mid ocean ridge
 The illustration at right shows the typical topography
of an ocean; the continental margin, ocean basin, midocean ridge and again to the next continental margin.
 Each of these areas has it’s own distinct features
Continental Margins:
zone of transition between
a continent and the adjacent
ocean basin floor
-Atlantic-thick layers of
undisturbed sediment cover the continental
margin.
-has very little volcanic or
earthquake activity.
 This is because the continental margins in the Atlantic
Ocean are not associated with plate boundaries, unlike
the Pacific Ocean.
 In the Pacific Ocean, where plate boundaries converge,
oceanic crust is plunging beneath continental crust in
a subduction zone.
 This force results in a narrow continental margin that
experiences both volcanic activity and earthquakes
 Ocean Floor features
 If you could travel from one coast to another across the
ocean floor, the first zone one would pass through
upon leaving land would be the continental shelf.
 The continental shelf is the gently sloping
submerged area extending from the shoreline.
 This shelf is almost nonexistent on some shorelines.
 However, on other shorelines in the world, the
continental shelf can extend outwards as much as 1500
kilometers.
 On average, the shelf is about 80 kilometers wide 130
meters deep at it’s seaward edge.
 The average steepness of the drop is only about 2
meters per kilometer drop; a slope so slight that the
human eye can barely perceive it.
 Continental shelves have
political and economic significance as well.
 Continental shelves contain important resources
such as mineral deposits, oil and natural gas deposits,
and enormous sand and gravel deposits.
 The waters of the continental shelf also contain
important fishing grounds, which are a significant
source of food.
 Continental Slope:
 Marking the seaward edge of the continental shelf is
the continental slope.
 The slope is steeper than the shelf and it marks the
transition from continental crust to oceanic crust.
 Although the steepness of the continental slope varies
from location to location; the average slope is 5
degrees.
 In some places, the slope can exceed 25 degrees. The
continental slope is a relatively narrow feature,
averaging only about 20 kilometers in width.
 Deep, steep sided valleys known as submarine
canyons are cut into the continental slope.
 These canyons may extend to the ocean basin floor.
 Most information suggest that submarine canyons are
formed by erosion, at least in part, by turbulent
underwater currents
 Turbidity currents are occasional movements of dense
sediment-rich water down the continental slope.
 They are created when sand and mud on the
continental shelf are disturbed, perhaps by an
earthquake, and become suspended in the water.
 Because the muddy water is denser than sea-water, it
flows down the slope.
 As it flows down, it erodes the bank away,
accumulating more sediment, and eventually cuts
these deep canyons into the shelf’s surface.
 Erosion from these muddy torrents over time is
believed to be the major force behind the carving of
these large canyons.
 Narrow continental margins, such as the one along the
California coast, are marked with numerous
submarine canyons created by runoff sediment from
the land.
Turbidity currents
 known to be an important mechanism of sediment
transport in the ocean.
 erode submarine canyons and deposit sediments on
the deep-ocean floor.
Continental rise
 In regions where trenches
do not exist, the steep continental slope merges into a more
gradual incline known as the
continental rise.
 Here the steepness of
the slope drops to about
6 meters per kilometer.
 Where the width of the
continental slope
averages only about
20 kilometers wide, the
continental rise may be hundreds of kilometers wide.
What are the three major
zones of the ocean
 Between the continental margin
and mid-ocean ridge
 includes deep ocean trenches, very flat areas known as
abyssal plains, and tall volcanic
peaks called seamounts and
guyots.
Deep Ocean Trenches
 long, narrow creases in the ocean floor
that form the deepest parts of the ocean.
Abyssal Plains:
 deep, extremely flat features. In fact,
these regions may be the most level areas on Earth.
 have thick accumulations of fine sediment that have
buried an otherwise rugged sea floor.
 sediments in abyssal plain are carried out there by
turbidity currents
 found in all oceans of the world.
 Atlantic Ocean has the most extensive abyssal plains
because it has few trenches to catch sediment carried
down the continental slope.
Seamounts and guyots:
 submerged volcanic peaks that dot the ocean floor
 found on the floors of all oceans. However,
the greatest number can be found
in the Pacific.
 Some can be found forming
at volcanic hot spots such as the
Hawaiian-Emperor Seamount chain.
 Once underwater volcanoes reach the surface, they
form islands. Over time, running water and wave
action erode these islands to near sea-level.
 Over millions of years, these islands gradually sink
below sea-level.
 This process occurs as the moving plate carries the
island away from the elevated oceanic ridge or hot spot
where they originated.
 These once active flat-topped but now submerged
structures are called guyots.
 locatednear the center of most ocean basins.
 is an interconnected system of underwater mountains
that have developed on newly formed ocean crust.
 This system is the longest topographic feature on
Earth running 70,000 kilometers around the world’s
oceans.
 A high amount of volcanic activity takes place along
mid-ocean ridges.
 This activity is associated with sea-floor spreading.
Sea-floor spreading occurs where divergent plate
boundaries are moving apart from each other.
 New ocean is formed at mid-ocean ridges as magma
rises between diverging plates and cools.
 Hydrothermal vents form along
mid-ocean ridges.
 zones where mineral-rich water, heated by the hot,
newly formed oceanic crust, escapes through cracks
in the oceanic crust into the water.
 As the super-heated mineral-rich
water comes in contact with the
cold water, minerals containing metals such as sulfur,
iron, copper, and zinc precipitate
out and are deposited.