Which main limitation of the old rope sounding method was removed by echo sounding in ocean floor mapping?
Correct answer: A
Echo sounding uses the return time of sound waves to estimate depth. Exam tip: link it with modern depth measurement.
Geography
Mapping of the ocean floor
महासागर तल का मानचित्रण
In this Class 11 Geography topic from “Distribution of Oceans and Continents,” students learn how the ocean floor is mapped and interpreted. They explore major features such as continental shelves, slopes, deep-sea plains, mid-ocean ridges, trenches and seamounts, and understand how soundings, sonar and bathymetric maps reveal underwater relief. The topic also helps connect ocean-floor patterns with plate boundaries, seafloor spreading and the changing distribution of continents and oceans.
TOPIC PRACTICE
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Hard · Level 3
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- Continuous and fast depth measurement became possible
- Colour of seawater was directly measured
- Age of continental rocks was found immediately
- Direction of ocean currents stopped
Hard · Level 3
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- Continental shelf
- Continental slope
- Abyssal plain
- Mid oceanic ridge
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- Flat abyssal plain
- Very gentle gradient
- Steep gradient or sharp drop
- Height of surface waves
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- Oceans have always been static
- Ocean floor is made only of sediments
- Continental shelf is the deepest part
- Zones of new oceanic crust formation were identified
Hard · Level 3
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- Convergent boundaries where subduction occurs
- Divergent boundaries where new crust forms
- Passive continental margins
- Stable abyssal plains
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- Because only volcanic lava flows there
- Because fine sediments cover irregularities
- Because depth never changes there
- Because they are always above sea level
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- Ocean trench
- Continental slope
- Guyot
- Submarine fan
Hard · Level 3
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- Ocean water is static
- Continental shelf cannot be volcanic
- Sediments are absent in trenches
- Seafloor spreading occurred almost symmetrically on both sides
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- Water is deeper
- Water is fresh
- Floor is certainly continental
- Waves have stopped
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- Because it is the deepest oceanic part
- Because fishing and mineral resources may be found here
- Because no sediment is deposited here
- Because it occurs only in the middle of open oceans
Hard · Level 3
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- To colour marine salinity
- To measure height of marine clouds
- To study submerged relief and depth
- To count coastal population
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- Deposition by marine glaciers
- Expansion of river delta
- Erosion of continental shelf
- Plates moving apart and magma rising
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- Measurement points were few and discontinuous
- Oceans had not formed then
- Sound could not travel in seawater
- Rivers did not reach oceans
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- All oceans are of the same age
- Understanding relative crustal age and depositional history
- Subduction has stopped everywhere
- The seafloor is always fixed
Hard · Level 3
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- Coast and beach
- Mid ridge and trench
- Continental slope and abyssal plain
- Seamount and guyot
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- It detects gravity related variations below through tiny sea surface height differences
- It counts marine species
- It only shows the colour of coastal sand
- It stops sound waves in the ocean
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- Shelf deepest and trench shallowest
- Shelf shallow and trench extremely deep
- Ridge always above sea level and shelf not always below
- Abyssal plain shallower than shelf
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- A seamount is only sedimentary
- A guyot always lies in a trench
- A guyot has a flat top while a seamount is generally conical
- A seamount is not found in the ocean
Hard · Level 3
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- Continental rise
- Abyssal hill
- Coastal plain
- Mid oceanic ridge system
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- Oceanic trench
- Continental shelf
- Abyssal plain
- Coral reef
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- It measures only one point
- It can record the floor shape over a wide swath
- It makes the seafloor flat
- It does not use sound
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- Lack of climatic evidence
- Lack of fossil similarity
- Unclear mechanism moving the continents
- Absence of coastlines on maps
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- New crust near the ridge
- Water at the ocean surface
- Oceanic crust away from the ridge
- Coastal sandy zone
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- Evaporation line of sea surface
- Shadow of storm clouds
- Oceanic magnetic pole
- Sediment deposition by submarine currents
Hard · Level 3
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- Isobath
- Isotherm
- Isobar
- Isohyet
If depth suddenly increases rapidly away from a continental margin which feature is most likely present?
Correct answer: B
The continental slope shows a rapid increase in depth over a short distance. Exam tip: shelf is gentle while slope is steep.
In a contour map of the ocean floor closely spaced depth contours indicate what condition?
Correct answer: C
Closely spaced isobaths show a steep gradient. Exam tip: topographic and bathymetric contours follow the same logic.
Mapping of mid oceanic ridges provided which most important clue for plate tectonics?
Correct answer: D
Mid oceanic ridges are linked with seafloor spreading. Exam tip: remember ridges as zones of new crust formation.
Deep oceanic trenches are generally found near which plate boundaries?
Correct answer: A
Trenches are mostly associated with subduction zones. Exam tip: treat trenches as the deepest and tectonically active parts.
Why are abyssal plains considered among the flattest parts of the ocean floor?
Correct answer: B
Sediments accumulate and smooth the irregular surface below. Exam tip: remember abyssal plains as deep and flat areas.
Which feature has a flat top indicating that it was once affected by erosion near sea level?
Correct answer: C
A guyot is a flat topped submerged seamount. Exam tip: distinguish guyots from conical seamounts.
Mapping of magnetic stripes on the ocean floor strengthens which explanation?
Correct answer: D
Symmetry of magnetic stripes on both sides of ridges supports spreading. Exam tip: connect magnetic stripes with seafloor spreading.
In sound wave based ocean mapping if the signal takes more time to return what does it directly mean?
Correct answer: A
Sound-based mapping uses the time taken by a sound signal to travel downward to the seabed and return to the ship. If the return takes longer, the signal has travelled a greater total distance. Since the speed of sound in seawater is treated as approximately known for this basic interpretation, a longer travel time indicates a greater depth of water. Thus, option A is correct. Water quality does not directly determine the return time in this question, and the result says nothing about whether the seabed is continental.
In practice, depth is calculated from travel time and sound speed, using the idea that distance equals speed multiplied by time; because the signal travels down and back, the measured distance is divided by two for depth. A deeper seabed produces a longer echo time, while a shallow seabed produces a shorter one. Therefore, the direct meaning of a longer return time is deeper water, not stopped waves or fresh water.
Why is mapping the continental shelf important in economic geography?
Correct answer: B
The shelf is a shallow and resource rich zone. Exam tip: link it with fisheries and petroleum potential.
What is the basic purpose of bathymetry in mapping the ocean floor?
Correct answer: C
Bathymetry is the study of depth and shape of the sea floor. Exam tip: understand it as mapping of oceanic relief.
If a map shows a long rift like valley along the middle of a ridge it may be linked with which process?
Correct answer: D
A rift valley along a mid ocean ridge is linked with divergent boundaries. Exam tip: remember rift and divergence together.
Why were older maps of the ocean floor more incomplete?
Correct answer: A
Older methods measured depth at limited locations. Exam tip: see modern sonar as a tool of wider coverage.
Mapping sediment thickness in ocean basins helps in which conclusion?
Correct answer: B
Sediment thickness indicates time and depositional environment. Exam tip: link thicker sediment away from ridges with older crust.
The continental rise is generally understood as a transition zone between which features?
Correct answer: C
The continental rise forms below the slope due to sediment accumulation. Exam tip: place it between slope and abyssal plain.
How does satellite altimetry indirectly help in mapping the ocean floor?
Correct answer: A
Tiny bulges and depressions of the sea surface relate to mass distribution below. Exam tip: treat it as indirect bathymetry.
Which pair correctly represents the depth arrangement of ocean floor features?
Correct answer: B
The continental shelf is shallow while trenches are among the deepest parts. Exam tip: understand depth order through landforms.
What is the most decisive difference between a seamount and a guyot?
Correct answer: C
A guyot is a flat topped form of an old submerged volcanic mountain. Exam tip: use summit shape as the clue.
What is the global network of long mountain chains on the ocean floor called?
Correct answer: D
The mid oceanic ridge is a vast submerged mountain system. Exam tip: connect it with seafloor spreading.
A narrow and very deep linear depression on a seafloor map is the identity of which feature?
Correct answer: A
The correct answer is A, an oceanic trench. On a map of the ocean floor, a trench appears as a long, narrow, and exceptionally deep depression. It commonly forms where one tectonic plate is forced beneath another at a convergent boundary; this process is called subduction. B, the continental shelf, is the shallow, gently sloping submerged edge of a continent, so it is broad and relatively shallow rather than very deep. C, an abyssal plain is a wide, nearly level deep-ocean floor, not a narrow linear depression. D, a coral reef is a biological or limestone structure built by corals in suitable shallow marine conditions, not a deep trench. Memory cue: trench = thin, long, deepest; shelf = shallow edge; plain = broad and flat.
Why is multibeam sonar better than single beam sonar in ocean floor mapping?
Correct answer: B
Multibeam sonar gives depth information across a wide area below the ship. Exam tip: link it with detailed bathymetric coverage.
Mapping of the ocean floor later helped reduce which weakness of the continental drift theory?
Correct answer: C
Seafloor spreading and plate tectonics clarified the mechanism of movement. Exam tip: connect Wegener's weakness with mechanism.
Which part of the seafloor generally becomes older with increasing distance from the mid oceanic ridge?
Correct answer: C
New crust forms at ridges and becomes older away from them. Exam tip: remember the relation between age and distance from ridge.
If a fan shaped sedimentary form is found at the base of a slope on the seafloor it may be related to what?
Correct answer: D
Sediments below the slope may form submarine fans. Exam tip: link fans with transport and deposition.
What is the line joining points of equal depth on a bathymetric contour map called?
Correct answer: A
Direct answer: A, isobath. In a bathymetric contour map, depth is measured below a reference sea level. A line joining places with the same depth is called an isobath, just as a contour line joins places of equal height on land. A is correct. B, isotherm, joins places with equal temperature. C, isobar, joins places with equal atmospheric pressure. D, isohyet, joins places with equal rainfall. All four words begin with ‘iso’, meaning equal, but their second parts identify the measured quantity: bath means depth, therm means temperature, bar means pressure, and hyet relates to rainfall. Memory cue: isobath = equal bathymetric depth.
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