Match the terms with the definitions.

Match the following dimensions with the correct geographical name

2.6 Look at the (R.P – 8.1.1) cross section of an imaginary ocean. The vertical scale is exaggerated for effect. Name the 10 major features of an ocean floor. Point them out.

Read the following text and fulfill the after-reading tasks. (R.P – 8.1.2, 8.1.3, 8.1.4)

Scarcely any ocean floor is more than 200 million years old. That long ago a single mighty ocean incorporating the Pacific surrounded one landmass. The land developed splits which widened into basins. The Arctic, Atlantic, and the Indian Oceans were created in this way.

Sea floor is always being made and destroyed by a process called sea-floor spreading. Growth occurs where crust is thinned by molten rock rising from the mantle beneath, or tugged apart by older, thicker crust sinking in the mantle elsewhere. Stretching splits vast chunks of oceanic crust, but the gaps are plugged by molten rock that wells up from below. Basalt sticking to the edges of such rifts formed the Mid-Atlantic Ridge and other vast underwater mountain chains called spreading ridges. Each widens by up to 10 in. (25 cm) a year.

Scientists believe the detailed process goes like this. First, molten rock wells up from deep down in the upper mantle region called the asthenosphere. The upwelling molten mass partly melts the rocks around it to make the oceanic crust. Gravity pulls the ridge flanks down and sideways. The resulting tension opens two main cracks along the ridge. Between these cracks the ridge’s middle sinks to form a central rift valley. Molten rock wells up through main and lesser cracks, then cools and hardens to become new ocean floor. Injections of fresh molten rock keep this spreading outwards from the central rift.

As upwelling continues, the rifting process is repeated. In time, rows of parallel ridges creep outward from their starting point, gradually sinking down to form the ocean’s abyssal plains.

Meanwhile great cracks called transform faults cut across the central ridge at right angles, offsetting short, straight sections.

(Lambert “The Field Guide to Geology” 1988, Cambridge University Press)

The diagram shows how a spreading ridge grows.

Fig. 44. Mid-ocean spreading ridge

1. Upwelling mantle partly melts and pushes up the oceanic crust above.

2. The bulging plate splits and a central block subsides. Molten rock rises through cracks at the block’s above.

3. More molten rock plugs gaps left as tension pulls old crust apart.

4. As new crustal blocks subside, fresh cracks appear.

The process is repeated.

TERMS

After-reading tasks.

Look through the text and pick out the terms, which have the following definition.

1. to include / to be part of

2. stress that pulls a solid body apart

3. to fill up

4. a lump

5. insertion of sedimentary material into a crack

6. horizontal normal separation

7. downward movement

8. part of the continental crust above sea level

9. oceanic crust forms along the Mid-oceanic ridge and spreads out laterally

10. subsurface water is transported toward the surface

Compose sentences, using the following words and phrases

3.1.3. Spreading ridge evolves several stages. Put the words according to the stages. Compose sentences to describe the process. (R.P – 8.1.2, 8.1.3)

Stage 1

Stage 2

Stage 3

Stage 4