1.2 Anatomy of a volcano Pay attention to the following terms in bold. (r.P. – 5.3)

Volcanoes take two main forms. Fissure or linear volcanoes chiefly emit basic lava from a crack in the Earth’s crust. Central volcanoes yield lava, ash and other products from a single hole. These products build a shield- or cone-shaped mound: the typical volcano shape. Central volcanoes can grow high and fast. In western Mexico in 1943 Paricutin grew 490 ft. (150 m) high in a week and reached 1500 ft. (450 m) in a year. In western Argentina extinct Aconcagua towers 22,834 ft. (6 960 m) above sea level; this is the highest mountain in the western hemisphere.

A cross section through an active central volcano would reveal these features. Miles below the surface lays the magma chamber- a reservoir of gas-rich molten rock under pressure. This pressurized magma may “balloon outward” against the surrounding solid rock until it can relieve the pressure by escaping through a weakness in the crust above. From the chamber, magma then rises through a central conduit. As magma rises the pressure on it is reduced and its dissolved gases are freed as expanding bubbles. Finally the force of gas blasts opens a circular vent on the Earth’s surface. From this outlet ash, cinders and flows of lava build the main volcano shield or cone. Vent explosions shape its top as an inverted cone or crater. Meanwhile, side vents on the flanks of the volcano release ash or lava that may build subsidiary cones.

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

Fig. 25. Volcano:

1 – lava flow; 2 – cloud (steam, ashes, rock clasts); 3 – main crater; 4 – secondary crater; 5 – secondary chimney; 6 – magma chamber; 7 – layers (lava, ashes)

2. Exercises

2.1 Read the text (once) more carefully and choose the correct alternative for these words:

1. Round-formed opening

2. upside-down

3. to let out

4. non-active

5. reservoir

6. to be under pressure

7. to be above

8. to decrease ( to become less in volume)

9. to explode

10. the form of a hill

2.2 Use two words from the corresponding line to complete each sentence.

1. emit magma bubbles products

2. tower ash mountain lava

3. linear cone chamber inverted

4. circular active extinct crack

5. fissures balloon conduit weakness

1. The volcano ___________ ____________such as ash and cinder.

2. The _________ ____________over the island.

3. The top of a volcano is like a ___________ ___________.

4. Volcanoes can be __________ or ___________.

5. __________ form as a result of the Earth’s _____________.

2.3. Give the Russian equivalent the following phrases:

1. volcanoes emit basic lava

2. typical volcano shape

3. volcanoes can grow high

4. above sea level

5. a cross section through a volcano

6. miles below the surface

7. gas-rich molten rocks

8. surrounding solid rocks

9. escape through a weakness in the crust

10. force of gases blast open

11. vent explosions shape its top

12. on the flanks

2.4 Match the words in the right column with the words in the left one.

pressurized volcano

single section

shield-shaped gases

extinct vent

western bubbles

cross crater

dissolved cone

circular conduit

expanding magma

inverted hole

subsidiary mound

central hemisphere