Mapping of the ocean floor

Depth and bottom structure are necessary for submarine cables. Exam tip: also connect mapping with infrastructure.

Information about depths and rises helps ships avoid dangerous areas. Exam tip: remember the safety reason.

Oil and gas resources may occur on continental shelves. Exam tip: remember resources with the continental shelf.

In many depth maps, darker colour indicates greater depth. Exam tip: match colour signs with the map key.

The map key explains the meaning of colours and symbols. Exam tip: treat the key as the base of every map.

A submarine canyon is a deep valley-like feature on the sea floor. Exam tip: remember it as a submerged valley.

Ridges and trenches show that the ocean floor has varied heights and depths. Exam tip: remember that the ocean floor is uneven.

In echo sounding, the instrument sends sound from a ship into the sea. Exam tip: remember ship-based survey.

A bathymetric map shows depths and features of the ocean floor. Exam tip: identify it from the word depth.

The shelf is shallow and gentle while the slope deepens more steeply. Exam tip: identify slope from the names.

Ocean floor features influence habitats of many marine organisms. Exam tip: remember the relation between floor and habitat.

The direct answer is option A: very deep parts of the ocean floor can be shown with deeper colours or isobaths. First understand the idea. A map cannot normally show depth by looking at the actual bottom, so it uses symbols. A bathymetric map represents underwater relief. Different shades of blue or other depth colours can show increasing depth. Isobaths are lines joining places that have equal depth, just as contour lines join places of equal height on land. Option A is correct because both deep colours and isobaths are accepted methods. Option B, flower pictures, gives no measurement of ocean depth and is decorative rather than geographical evidence. Option C, counting trees, is unsuitable because trees do not measure underwater depth. Option D, sunlight amount, may affect the sea surface or climate but does not directly indicate the depth of the floor. Thus A is the only relevant scientific answer. Exam cue: contours show equal height on land, while isobaths show equal depth under water.

A ridge is a long, narrow, elevated landform. On the ocean floor, an underwater ridge is a raised belt that may extend for very great distances. Mid-ocean ridges are especially important because they are associated with places where new oceanic crust can form as plates move apart. The word ridge therefore indicates a raised linear feature, whether it occurs on land or beneath the sea.

The correct choice is A, ridge. A field bund is a small human-made embankment, a city road is a transport route, and a sand dune is a mound of wind-deposited sand. None of these describes a long elevated belt on the seabed. The clue is the combination of “long” and “elevated”: it points to a raised underwater line rather than a flat plain or an isolated mound. Hence, option A is the appropriate geographical term.

Mapping replaces guesses with measured data-based information. Exam tip: write the importance of scientific measurement.

Oceans are vast and deep, so accurate measurement was difficult. Exam tip: remember the need for modern technology.

Coastal countries use ocean floor information for navigation, resources and risk management. Exam tip: connect usefulness with planning.

Echo sounding is a method to find ocean depth. Exam tip: connect it directly with depth measurement.

Showing relief makes underwater mountains, plains and trenches understandable. Exam tip: treat the sea floor as a landform surface too.

Ocean trenches are counted among the deepest marine parts. Exam tip: remember both deep and narrow.

A plain on the ocean floor, especially an abyssal plain, is a broad, nearly level area submerged in deep parts of the ocean. A land plain, in contrast, lies on the Earth’s terrestrial surface. Option B is not correct because fine sediment deposition, not wind action alone, is chiefly responsible for smoothing abyssal plains. Exam tip: remember an abyssal plain as a sediment-covered flat region of a deep ocean basin.

Closely spaced lines indicate a rapid change in depth. Exam tip: remember the rule like contour lines.

Widely spaced isobaths show gradually changing depth. Exam tip: identify slope from spacing of lines.

The ocean floor is the submerged part of Earth's surface. Exam tip: understand Earth's surface as both land and underwater areas.

It shows oceans not just as water but as areas with varied features. Exam tip: study ocean floors structurally.

The main work of ocean floor mapping is to clarify depths and features. Exam tip: connect it with ocean floor relief.