Unit 8 the restless crust part 1: oceanic crust

1. Comprehension

1.1 Vocabulary

Pay attention to the pronunciation of the geographical terms and especially to the pronunciation of numbers

Pacific Ocean	Marianas Trench
Mid-Atlantic Ridge	Arctic Ocean
Atlantic Ocean	Ascension Island
Mt. Everest	Indian Ocean

97 per cent 7.5 per cent

71 per cent 8.5 per cent

12,400 ft. (feet) ≈ 3 700 m

650 ft. ≈ 200 m

11,500 ft. = 3 450 m

3,300 ft. ≈ 1000 m

10,000 ft. = 3000 m

37,000 mi. (miles) ≈ 60 000 km

35,840 ft. = 10 752 m

3300 ft. - 33 hundred feet

Pay attention to the bold terms and expressions in the text

continental shelf	континентальный (материковый) шельф
continental slope	континентальный (материковый) склон
submarine canyon	подводное ущелье (каньон)
continental rise	континентальное (материковое) подножие
submarine plateau	подводное плато
abyssal plain	абиссальная равнина
seamount	морская гора
spreading ridge	спрединговый (срединно-океанический) хребет
trench	желоб
island arc	островная дуга
trough	впадина, мульда
guyot	гайот
continental side	континентальная сторона, склон
to strip off	обнажать
sheath	оболочка, покров
plateau	плато
peak	вершина горы, пик
to submerge	погружать
rim	край
to descend	опускаться; нисходить
slope	склон; крыло складки
cleft	трещина; расселина
turbid	мутный
surroundings	окружение; среда
mountain chain	горная цепь
tableland	плоскогорье, плато

1.2 Read the text «The Ocean Floor». Pay attention to the diagram. Fulfill the exercises after the text. (r.P – 8.1.1)

Oceans and their seas hold 97% of all surface water, and cover some 71% of the Earth to an average depth of 12,400 ft. (3700 m). Stripping off this watery sheath would reveal valleys, plateaus, peaks and plains. We show ten features of the ocean floor.

Continental shelf- a continent’s true but submerged and gently sloping rim, descending to an average depth of 650 ft. (200 m). Continental shelves occupy about 7.5% of the ocean floor.

Continental slope- a relatively steep slope descending from the continental shelf. Such slopes occupy about 8.5% of the ocean floor.

Submarine canyon- a deep cleft in the continental slope, cut by turbid river water flowing out to the sea.

Continental rise- a gentle slope below the continental slope.

Submarine plateau- a high seafloor tableland.

Abyssal plain- a sediment-covered deep-sea plain about 11,500-18,000ft (3450-5400 m) below sea level.

Seamount- a submarine volcano 3300ft. (1000 m) or more above its surroundings. Guyots are flat-topped seamounts that were once volcanic islands.

Spreading ridge- a submarine mountain chain generally 10,000 ft. (3000 m) above the abyssal plain. A huge system of such ridges extends more than 37,000 ft. (60000 m) through the oceans. The Mid-Atlantic Ridge surfaces in places as volcanic islands such as Iceland and Ascension Island.

Trench- a deep, steep-sided trough in an abyssal plain. At 35,840 ft. (10752 m) below sea level (deep enough to drown Mt. Everest). The Pacific’s Marianas Trench is the deepest part of any ocean.

Island arc- a curved row of volcanic islands, usually on the continental side of a trench.

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