Theory question 204
Oceans and Lakes(a) Draw a diagram of the relief of the ocean floor showing the following (i) Continental shelf (ii) Continental slope (iii) Ocean deep
(b) Describe the main characteristics of any two of the features shown
(c) Highlight the economic importance of continental shelves to man
Show the model answer
(a) Cross-section from land to sea showing the gently sloping continental shelf, steep continental slope, deep-sea (abyssal) plain and a narrow ocean deep/trench, with sea level marked
(b) Continental shelf: gently sloping submerged edge of the continent, to about 180 m (100 fathoms) deep, varying width; covered with sediment; sunlight reaches the bottom so plankton thrive
Continental slope: steep slope from the shelf edge down to 3,000-4,000 m; cut by submarine canyons
Ocean deep: long narrow trenches over 6,000 m deep, often near island arcs/fold mountains (Mariana Trench about 11,000 m)
(c) Richest fishing grounds (plankton); oil and gas deposits (Niger Delta offshore, North Sea); other minerals and sand/gravel; good harbours and ports; tourism and recreation
Label depths on the diagram.