Year 6. Geography. Revision

Transcription

1 Year 6 Geography Revision November 2016

2 Rivers and World knowledge Why early settlers chose to live near rivers. How the water cycle works and the meaning of the terms evaporation, condensation, precipitation, transpiration, surface run-off, groundwater flow, percolation. There are six important processes that make up the water cycle. 1. Condensation - the opposite of evaporation. Condensation occurs when a gas is changed into a liquid. 2. Percolation - is an important process where rain water soaks into the ground, through the soil and underlying rock layers. 3. Surface Runoff - Much of the water that returns to Earth as precipitation runs off the surface of the land, and flows down hill into streams, rivers, ponds and lakes. 4. Evaporation - the process where a liquid, in this case water, changes from its liquid state to a gaseous state. 5. Precipitation - When the temperature and atmospheric pressure are right, the small droplets of water in clouds form larger droplets and precipitation occurs. The raindrops fall to Earth. 6. Transpiration - As plants absorb water from the soil, the water moves from the roots through the stems to the leaves. Once the water reaches the leaves, some of it evaporates from the leaves, adding to the amount of water vapor in the air. This process of

3 evaporation through plant leaves is called transpiration. THE WATER CYCLE Understand the difference between impermeable and permeable rock (impermeable meaning water cannot go through it, permeable meaning the opposite). Ox-Bow Lake formation: As the outer banks of a meander continue to be eroded through processes such as hydraulic action the neck of the meander becomes narrow and narrower. 1. Eventually due to the narrowing of the neck, the two outer bends meet and the river cuts through the neck of the meander. The water now takes its shortest route rather than flowing around the bend. 2. Deposition gradually seals off the old meander bend forming a new straighter river channel. 3. Due to deposition the old meander bend is left isolated from the main channel as an ox-bow lake. 4. Over time this feature may fill up with sediment and may gradually dry up (except for periods of heavy rain). When the water dries up, the feature left behind is known as a meander scar.

4 RIVERS DEFINITIONS Drainage Basin: The area of land that is drained by a river and its tributaries. The Watershed: The boundary of a river basin is called the watershed. Source: Where the stream begins: usually where there is a spring, and quite high up. Confluence: Where two rivers or streams meet. Meander: A bend in a river. Floodplain: The flood plain is the flat land of the river valley close to the river banks. Mouth: The end of the river. The mouth may be where the river meets the sea, a lake or a larger waterway. Most rivers flow out into the sea, and this is where they end their journey. Estuary: A drowned river valley in a coastal lowland area. Occurs near or at the mouth of a river, where the tide meets the current and the fresh and salt waters mix. Tributary: A small river that joins onto a bigger river. Waterfall: A cascade of water falling from a height. Lake: A large body of water surrounded by land. Delta: A depositional landform formed at the end of a river when it loses all its energy and deposits all the sediment it was carrying. V shaped valley: River erodes vertically creating valleys with steep slopes.

5 U shaped valley: River erodes both vertically and laterally creating valleys that have more gentle slopes. Major Rivers of the World Mississippi flows from north to south in the USA and ends in the Gulf of Mexico Amazon flows from west to east through South America and ends in the Atlantic Ocean Nile flows from south to north through northern Africa and ends in the Mediterranean Sea Congo flows from east to west through central Africa and ends in the Atlantic Ocean Gages flows from north to south through India and ends in the Bay of Bengal (Indian Ocean) Yangtze flows from east to west through China and ends in the South China Sea