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2. The hydrosphere 2 © Zanichelli editore 2015

3. Oceans and seas 3 © Zanichelli editore 2015

4. The hydrosphere is a dynamic system 4 The hydrosphere is a dynamic system: in any environment water moves due to the effect of gravity and wind and it is subject to changes of state due to changes in temperature. Water is the most powerful exogenous agent. © Zanichelli editore 2015

5. The distribution of superficial waters 5 The majority of water on Earth is liquid in seas and oceans while another portion is solid in polar caps and glaciers, part is held in soil and a small percentage is in lakes and rivers. © Zanichelli editore 2015

6. Oceans and seas 6 Oceans occupy vast, deep depressions on Earth’s surface, their floors are continuously modeled and destroyed by movements of tectonic plates. Seas are smaller, closed and shallow basins of salty water, surrounded by land. © Zanichelli editore 2015

7. Physical properties of salt waters: salinity 7 Water in seas and oceans are solutions in which salts are present. Salinity fluctuates around an average of 35‰. SaltQuantity (g/L) Percentage on total salts NaCl27.21377.76% MgCl 2 3.80710.87% MgSO 4 1.6584.73% CaSO 4 1.263.6% © Zanichelli editore 2015

8. Physical properties of salt waters: temperature 8 Temperature is another physical property that influences the movements of waters. Close to the surface, the temperature of waters is influenced by climatic zones. Deep waters have an average temperature of around -1 °C. © Zanichelli editore 2015

9. Waves /1 9 Waves are irregular and oscillatory movements caused by the wind. In open waters, oscillatory waves do not move masses of water. Translation waves, which form along the coast, can move masses of water. © Zanichelli editore 2015

10. Waves /2 10 © Zanichelli editore 2015

11. Currents 11 Currents are slow, regular movements of big masses of water, which differ from the surrounding waters for temperature, salinity, density and color. There are warm and cold currents; they can influence the climate of the regions they touch. © Zanichelli editore 2015

12. Tides /1 12 Tides are periodical oscillations of the level of surface in oceans or seas. They are due to the gravitational attraction of the Sun and Moon and the effect of the centrifugal force associated with the motion of the Earth-Moon system. © Zanichelli editore 2015

13. Tides /2 13 © Zanichelli editore 2015

14. The coastline 14 The morphology of the coastline depends on the phenomena involved in rock formation as well as endogenous and exogenous processes. Erosion occurs on high coastlines where cliffs form, while beaches form where deposits of eroded materials dominate. © Zanichelli editore 2015

15. Continental waters 15 © Zanichelli editore 2015

16. Freshwater 16 Freshwater is distributed across continents and can be divided into: underground waters; watercourses; lakes; glaciers. © Zanichelli editore 2015

17. Underground waters 17 Underground waters derive from precipitation that percolates into the subsoil. They can spontaneously emerge as springs. © Zanichelli editore 2015

18. Watercourses 18 Water channeled into a bed is called watercourse. It is fed by a drainage basin, which is the area where all water flows into the same bed. © Zanichelli editore 2015

19. Rivers model valleys and plains 19 If the flow rate is nearly constant during the year, the watercourse is called a river, otherwise it is called a stream. Watercourses model the landscape around them, through the erosion of rocks and soil and the transportation and sedimentation of sediment. Rivers create V-shaped valleys by their erosion. © Zanichelli editore 2015

20. Deltas and estuaries 20 River mouths can be: deltas if they are are fan-shaped and open into a calm marine basin; or estuaries if they are funnel-shaped and open into a large basin with strong currents or tides. © Zanichelli editore 2015

21. Lakes 21 Lakes are masses of water that occupy continental depressions. They do not communicate directly with seas or oceans. With time, they can transform into ponds or marshes, until they disappear. © Zanichelli editore 2015

22. Glaciers 22 Glaciers are permanent bodies of compact snow and ice. Polar glaciers in the Antarctic, Greenland and Iceland form vast ice caps which are almost immobile. Mountain glaciers can be found at all latitudes above the persistent snow line. Mountain glaciers are formed by three elements: accumulation zone where snow accumulates and becomes ice; glacier tongue which flows on the rocky bottom like a slow ice river; glacier head - the terminal part of a glacier. © Zanichelli editore 2015

23. Glaciers model the land 23 U-shaped valleys, with flat basins and steep walls, are formed by mountain glaciers. Materials eroded by a glacier are transported along the valley; they deposit behind or around the glacier head. Moraines are masses of sediment left by the glacier. © Zanichelli editore 2015

24. The hydrological cycle 24 The different sectors of the hydrosphere are connected by a hydrological cycle triggered by the Sun. It also involves the atmosphere, lithosphere and biosphere. © Zanichelli editore 2015