Download 2.00 Bathymetry notes

2.00 Bathmetry Lecture notes
Bathymetry of the Ocean Floor
Text Book Reading Pages – 37 - 42
The ocean floor is mapped by SONAR.
(______________________________________________________________)
Depth = (time x 1500 m/sec)/2 (round trip) At ____________ degrees Celsius
Relationship above and below the water
Ocean Floor Topography
Major features:
___continental shelf, ___trenches, ___abyssal plains, ____mid-ocean ridges.
After 1920’s, these features could be mapped in detail by sonar (bouncing sound waves off the
ocean floor).
2.00 Bathmetry Lecture notes
______________________________________
+Area of shallow water along ___________________ continental margin (not
an active plate boundary).
+Shelf drops off abruptly at outer edge.
+Much of shelf was above sea level during past __________________ periods.
Important processes at a passive margin
Accumulation of ______________________.
Subsidence (_______________) of crust as sediment is added.
Mass wasting at edge of continental shelf.
Turbidity currents (large rapid flows of dense, sediment-laden water).
______________________________________
+gentle slope at the base of the continental slope caused by:
- turbidity currents - deposition of sediment by underwater landslides
and other processes that carry mud, sand & silt down the slope
- occurs at the ______________ of the slopes & gently slope seaward to
the deep sea floor
__________________________________
+Occur along active margins (present-day plate boundaries) where
_________________________ is taking place
+deepest part of the ocean floor, typically 3 - 4 km deeper than surrounding
seafloor
+relatively narrow, few 10’s of km wide and thousands of km long
+most occur in the Pacific, mostly western Pacific, but most of the Pacific is
surrounded by trenches
+deepest spot in the oceans is the Challenger Deep in the
_____________________ Trench, 11,035 m
+trenches are associated with ____________ volcanoes and earthquakes
-most are near chains of volcanic islands
Abyssal Plane
+_________________________ making up much of the ocean floor apart from
trenches and mid-ocean ridges
Mid-Ocean Ridges
+_____________________________ features on earth.
+Broad ridges with a deep rift valley down the center.
+Offset by faults.
+Location where basaltic lava flows erupt.
+Age of the ocean floor
2.00 Bathmetry Lecture notes
-Detailed studies in 1950’s showed that there are bands of similar aged
rocks parallel to mid-ocean ridges.
-Bands get older with greater distance from the ridges.
________________________ - ripple marks observed on the floor of submerged
canyons and sediments fanning out at the end suggest they were formed by moving
sediments and water
- cut by turbidity currents - caused by earthquakes or buildup of sediment on a
steep slope
- fast moving avalanches of mud, sand and water that flow down slope, erode
walls and pick up sediment
- as flow reaches bottom, it slows down, fans out and the sediment settles out
__________________________ cut through the shelves and slopes, look like river
valleys on land, cut during periods of low sea level by turbidity currents, some
associated with major rivers, e.g. Hudson Canyon
Ocean Floor is seaward of the continental margin covers 30% of the earth's surface
compared to 29% covered by the continents - in most places, seafloor is a flat plain Abyssal Plain
+covered by sediment deposits of turbidity currents
+covering an irregular seafloor plain interrupted by:
_________________________ (< 1 km above the seafloor) - cover -80% of the
Pacific and -50% of the Atlantic sea mounts (rise steeply, sometimes above the
surface to form islands)
_________________________ (flat topped seamounts found most often in the
Pacific)
__________________________, usually I - 1.7 km below the surface
- many have ancient coral reefs on top indicating that they were once at the
surface
- flat tops due to wind & rain erosion
- subsided due to their own weight & crustal movement
Basins
Abyssal plains
Abyssal hill
Seamount
Guyot
Trenches
Mid Ocean ridges
Rift Valley