Rivers Rough PDF

Rivers o River erosion happens when a river flows over the land. o Rivers carry different types of weathered material— hence why they’re a muddy colour. o This transported material is called a river’s load. o This material is sand, stones and slit. o This wears away the land. o As the load goes...

Rivers o River erosion happens when a river flows over the land. o Rivers carry different types of weathered material— hence why they’re a muddy colour. o This transported material is called a river’s load. o This material is sand, stones and slit. o This wears away the land. o As the load goes along the river it wears away at the river’s sides. o The load gets smaller on the rivers journey to the sea. o Rock is worn away by the force of the river. Upper Course oRivers flow faster on steep land. oFaster flowing rivers can transport a heavier and larger load. oAfter heavy rain, rivers in highland areas can move large boulders. oSlowly the boulders move along the river’s course becoming smaller as the wear away. oThe movement of these boulders and rocks along the river bed causes downward erosion. oThis produces a deep valley with steep sides. Waterfalls and Rapids Waterfalls and rapids can occur at any part along a river’s course. A waterfall is a sudden drop in a river’s gradient. Rapids are part of a river’s course where the water flows faster but there is NO sudden drop in height. The river flows over bands of harder and softer rock The river undercuts the harder rock leaving an overhang. Softer rock is more quickly eroded. Overhanging rock collapses into the plunge pool. The river forms a plunge pool below the waterfall. Gorges and Canyons Gorges and canyons are deep-sided valleys that have been formed by downward river erosion. Gorges are linked to waterfalls. Backwards erosion causes the waterfall to retreat upstream and it carves a gorge in the process. A gorge is usually straighter than a canyon. A canyon usually forms when a river flows faster and downward erosion increases. This can happen if there is no more water in the river, a drop in sea level, or the land is uplifted. These make the river flow faster. Middle And Lower Course Sideways erosion is more noticeable in the lower and middle courses. River valleys are wider. There is more deposition of the river’s load. Rivers often have large bends. Meanders A meander is formed by both erosion and deposition. The river water flows faster on the outside of the bend—this erodes the bank. The river water flows slower on the inside of the bend—Deposition occurs here. Slow-flowing water deposition Fast-flowing water Erosion Ox-bow Lakes As erosion continues it pushed the bend of the meander downstream. This narrows the gap between different meanders—this cap is called the meander neck. The river will erode through the meander neck and make a new channel. Deposition from the river will cut off the original meander, leaving it as an ox-bow lake. In time the ox-bow lake will dry up and be left as a meander scar. MEANDER MEANDER NECK NEW RIVER NEW OX- CHANNEL BOW LAKE Levees Levees are natural mounds on river banks. They are formed when a river floods and deposits sand and silt on the river bank. Frequent floods increase the height of levees. Deltas Deltas form at the place where a river flows into the sea or lake. The river loses its energy when it meets another mass of water. This causes it to deposit the remainder of its load. Deltas form at the place where a river flows into the sea or lake. The river loses its energy when it meets another mass of water. This causes it to deposit the remainder of its load. Wave Erosion Ocean waves can release a large amount of energy when they wash against the land. Waves carry silt, sand and stones. Waves continuously erode the coast. Erosion is much greater when waves are larger during storms and strong winds.  Headlands & Bays Headlands are pieces of land that stick out into the sea. Bays are carded areas in between headlands. Rocks of different hardness and resistance are the main cause of headlands and bays. Waves wear away soft rock Headlands stick more quickly forming a bay. out as rocky areas Cliffs A cliff is a steep wall of /face rock that is formed by wave erosion. Wave cut Waves erode the base hollow of rocks on the coast causing the rock above to collapse. As erosion continues the cliff face retreats inland. The old base of the cliff remains as a rocky area called a wave-cut platform.  Caves, Arches & Stacks Caves, arches and stacks are formed by wave erosion. Each feature is part of a sequence of erosion that takes a long time to form. CAVE Waves attack weak points in the cliff. Small caves form around the weak points. ARCH Two caves may form back-to-back on either side of a headland. An arch forms when the two caves meet. STACK Wave erosion at the base of the arch and weathering above it weaken the arch. Eventually the arch collapses and forms a stack. A stack is a column of rock which stands apart from the land.  Wave Deposition Materials eroded from headlands are transported in waves and currents. This material is then deposited along the coast. Beaches This is the most common for of deposition. A beach is an area of loose sand or stones that covers parts of the coast between low tide and high tide. Some of the material along the beach is transported by rivers and is then spread along the coast y waves. If waves push loose material up the beach at an angle, the material rolls down the beach at a different angle. This action is called the longshore drift. Material eroded from headlands. Material deposited from a river. BEACH re drift sho Long Spits Spits are narrow ridges of sand that stick out into the sea or river mouth. They are formed by the action of waves and the longshore drift. When there is a bend in the coast, the movement of material still continues in the direction of the longshore drift. This causes a spit of sand to build up, sticking out away from the land. Spits will continue to grow until deposition can no longer occur (due to changes in currents or the presence of a river). Sometimes water is trapped behind the spit. This area might become a marsh of mud and plants called a salt marsh. River stops spit from flowing Direction of waves Bars Bars form when a spit grows across a bay and joins two headlands. An area of water called a lagoon forms behind the bar. The lagoon may be filled with water from the land and also with sea water that washes over the bar from the sea, during the very high tides. A lagoon may eventually turn into a salt marsh. LAGOON BAR ongshore drift Headlands Wave direction L  Ice Erosion Glaciers are masses of ice that move slowly downhill. Glaciers erode the land. When they melt they dump all the material carried in the ice to form deposition features. This main kind of erosion is caused by abrasion. Abrasion wearing away by friction—grinding and rubbing. Cirques These are bowl shaped hollows in glaciated mountain areas—these are often the places where a glacier begins. Snow accumulates in a hollow. As more snow falls, the lower layers of snow become compressed and turn into ice. It takes thousands of years before the ice becomes a glacier. The weight of the glacier and the force of gravity cause the glacier to move. As it moves it erodes into the hollow, making it deeper. Arêtes And arête is a ridge on a mountain which has been eroded by a series of glaciers on both sides. If a pointed peak remains it is called a horn. Horn Cirque Arête Ice hollow Cirque  U-shaped Valleys The glaciers that erode cirques and arêtes join up to form bigger glaciers in the lower areas. These valley glaciers are much larger and cause greater erosion. As a valley glacier grinds its was down a valley, it cuts off the spurs that protrude into the valley. The remains of the spurs are referred to as truncated spurs. The glacier scours out and widens the normal V shape of the valley bottom, to a U shape. Horn Arete Cirque Truncated Spurs Glacier U-shaped Valley Features Of Deposition In Glaciated Landscapes Terminal and lateral moraines Moraine ‘water rock’ Moraines are the rock left at the side and the end of the glacier as it melts. Lateral moraines are on the side of the valley. Terminal Moraines are at the end of the valley. Eskers Theses are the meandering ridges of sand and stones formed by rivers flowing under the glacier. Drumlins These are rounded hills about 50 meters high and about 500 meters long. It is not exactly sure how drumlins were formed. But it is believed that materials were deposited beneath the ice and the shaped by the movement of the glacier. Drumlins Terminal moraine Esker