Weathering And Erosion

Worksheet No.5 WEATHERING AND EROSION Unit 13 WEATHERING AND MOVEMENT  Name the four agents of erosion Agents of Erosion: Running. Water, Glaciers, and Wind Reference:www.science.sjsu.edu/scied/255/PDF02/erosion  Describe the different types of mechanical or physical weathering. Mechanical Weathering Mechanical weathering involves the breaking down of rocks due to a kind of pressure exerted on the rock, which can be due to various reasons. The primary method of mechanical weathering is the alteration in size that the particle would go through and it would definitely grow smaller with weathering. Here are the types of Mechanical Weathering. Exfoliation is the process wherein the rocks break in sheets along the joints that they have parallel to the earth surface. It mostly occurs when a large mass of rock is brought to the surface level as a result of tectonic movements, which thrusts the rock upwards. Even after the rock layer comes on the surface of the earth the exertion of pressure continues which results in the formation of cracks or sheet joints. Now due to pressure the rock disintegrates along the crack to expose the underlying layer of rock. This process is called Exfoliation. Abrasion is the type of mechanical weathering which is very common in the deserts. Abrasion means that the the surface of the rock is weathered due to the action of an abrasive agent, which removes the upper layer of the rock, by friction. In the deserts the poles meant for electric wires tend to topple as the base of the pole goes through the abrasive actions and becomes weathered, resulting in the toppling down of the poles. It happens so that wind carries the sand particles that chafes against the rock and wears it down. Freeze and Thaw Weathering is the type of weathering which is common in places where the night temperature goes down below freezing point thus freezing the weather that is collected in the cracks and crevices of the rocks. As we all know when water freezes its volume increases and as result of which the crack expands. In the morning the frozen water thaws and gives space to more water, which follows the same procedure. After repeated freezing and thawing, ultimately the rocks breaks along the crevice leading to fragmentation of the one whole rock into many rock particles. By Poushali Ganguly Published: 3/15/2008 Reference: www.buzzle.com/articles/mechanical-weathering.html

 Describe the different types of chemical weathering. Hydrolysis is an exchange reaction involving minerals and water. Free hydrogen (H+) and hydroxide (OH)- ions in water are able to replace mineral ions and drive them into solution. As a result, the mineral's atomic structure is changed into a new form. It is a process whereby silicate minerals like potassium feldspar are weathered and a clay mineral is formed. 2KAlSi3O8 + 2H+ + 9 H2O -> Al2Si2O5(OH)4 + 4H4SiO4 + 2 K2+ Hydration involves the absorption of water like which occurs during the conversion of hematite to limonite: 2Fe2O3 + 3H20 -> 2Fe2O3 . 3H20 Some geoscientists question whether hydration is a true chemical weathering process because the process is readily reversible and the new product is not chemically different from its precursor. Some would rather call hydration a physical weathering process. Carbonic acid action involves combination of carbon dioxide and water. Though present in pure water, carbon dioxide dissolved in water provides ions that produces free hydrogen. Carbon dioxide in the atmosphere combines with rain water to form carbonic acid (H2CO3):

H2O + CO2 -> H2CO3 Though weak, when carbonic acid is combined with a mineral like calcite (CaCO 3) common to limestone, calcium and bicarbonate ions are released and carried off by groundwater.

CaCO3 + H2CO3 -> Ca+2 + 2 HCO-3

Reference:

www.uwsp.edu/...weathering/chemical_weathering.html

 Describe the different types of mass wasting.

Types of mass movement – gravity causes mass movement, the force of gravity moves rocks and other materials downhill. • Landslides – most destructive, rapid form of erosion – may not only move rock an sediments but trees, plants, roads, what ever is in the way. • Mudslides – rapid downhill movement of a mixture of water, rock and soil- often occur after heavy rains but like landslides can be triggered by earthquakes. • Slump – movement of a mass of rock and soil, move down together as one. Creep – very slow downhill movement of rock and soil. Only noticeable by looking at objects such  What is the importance of unloading? As the weight of those overlying rocks is removed, the underlying rocks feel a negative stress in the vertical direction. Relaxation in this direction causes the rocks to buckle and break into smaller segments at a variety of spatial scales. This in itself constitutes some sort of weathering. Then the availability of additional pore spaces in the rock due to the breakup is likely to induce increased groundwater flow through the rock, increasing weathering even further. Unit 14 RUNNING WATER  Describe the three ways water moves sediments.

Abrasion – the wearing away of rock by a grinding action Load – the amount of sediment a river carries is called its load. Turbulence – a type of movement of water in which, rather than moving down stream, the water moves every which way. Reference:scorescience.humboldt.k12.ca.us/.../types_of_mass_wasting.htm

 Describe how valleys widen? The processes involved are:(1) retreat of valley sides by weathering and local corrasion by streams and (2) shifting of channels by plugging the main channel at the basin head and by tributary deposition on the basin floor. Repeated shifting of the channel over a long period and flood scour to an average depth produces a flat bedrock floor.

Reference: bulletin.geoscienceworld.org/cgi/content/abstract/60/11/1771

 Describe how meander forms.

Meander formation is a somewhat equivocal term referring to the natural factors and processes that result in meanders. The waveform configuration of a stream is constantly changing. Once a channel begins to follow a sinusoidal path the amplitude and concavity of the loops increase dramatically due to the effect of helical flow sweeping dense eroded material towards the inside of the bend, and leaving the outside of the bend unprotected and therefore vulnerable to accelerated erosion, forming a positive feedback loop. In the words of Elizabeth A. Wood.

 Describe how delta forms. Delta (geologic formation), deposit of soil or silt formed wherever a swift stream or river empties into a lake, ocean, or slower river, so called because its triangular shape resembles the Greek letter Δ (delta). The term was first used by the Greek historian Herodotus in the 5th century BC to describe the Nile delta. The triangular shape and the great width at the base are due to blocking of the river mouth by silt, with resulting continual formation of distributaries at angles to the original course. Deltas are usually characterized by highly fertile soil. The combined delta of the Ganges and Brahmaputra rivers in India, and the deltas of the Nile River in Egypt and the Mississippi River in the United States are the world’s largest.  How does a delta differ from an alluvial fan? delta forms when a river empties into a larger body of water. An alluvial fan forms on land where a river emerges from a mountainous area and flows out onto a more gently sloping plain. The decrease in slope causes the river to decelerate and deposit sediment, forming an alluvial fan. Reference: -- Sharon Gabel ([email protected]), December 16, 2002.  What is stream piracy? Stream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighboring stream. Reference: www.ask.com Unit 15 Glaciers  How does a glacier form? Glaciers can only form in Polar Regions or high mountains. This is because in those areas summer does get hot enough to melt all of the snow. The glaciers will not be at any more than a 30-degree angle on the bottom. If the snow/ice mixture is at more of an angel than that then it will fall as an avalanche (crumble and separate). A glacier is only considered a glacier after it has begun moving. Reference: www.ask.com

 What causes a glacier to move and how quickly can it move? Once the depth of snow and ice reaches more than 30 to 40 meters, gravity begins to pull the glacier down hill. Reference: www.ask.com  Which parts of a glacier and its tributaries move most quickly? It moves quicker in the middle and slower around the sides. Reference: www.wikianswers.com  Which continent does not have any glaciers? Why? Most of the world's glaciers are found near the Poles, but glaciers exist on all of the world's continents, even Africa. Australia doesn't have any glaciers; however, it is considered part of Oceania, which includes several Pacific island chains and the large islands of Papua New Guinea and New Zealand. Both of these islands have glaciers. Reference: nsidc.org/glaciers/story /

 Describe how a glacier moves. Glacier movement depends on whether it is warm or cold. This depends on the pressure melting point (PMP), which is when ice is on the verge of melting. An increase in pressure can increase melting and therefore movement due to lubrication. Accumulation is the inputs of the glacier system by precipitation as snow, avalanches, debris as rocks and melts water. Ablation is the outputs of the glacier system which include melt water, till-rock deposition, calving iceberg, evaporation and wind erosion. If there is more accumulation than ablation then the glacier advances due to gravity. If there is less accumulation than ablation there is more melt water, which acts as a lubricant, the glacier then moves down the valley but retreats due to climate, altitude and latitude. There are two types of glaciers, cold polar and temperate. Reference: www.ask.com Unit 16 Wind, Waves and Current  Identify the different types of dunes. crescentic, linear, star, dome, and parabolic. Reference: www.ask.com  How do dunes migrate? Sand can only be moved by strong, steady winds. The air must be moving at least 15 miles per hour to be able to pick up sand grains. In the Tularosa basin, it is primarily between February and April that the winds are strong enough. These winds are called unidirectional winds because they always move in the same direction, from the southwest to the northeast. As the wind blows, it pushes the sand ahead of it, so individual dunes are slowly moving to the northeast. Reference: www.wikianswers.com

 Identify the parts of the wave. The very top of a wave is called the crest. They very bottom is the trough. From one crest to the next is the wavelength. The center of the wave is the medium, or rest position. From the medium to the crest is the amplitude. Reference: www.wikianswers.com  How do breakers form? As waves approach landmasses, the wave base begins to contact the sea floor and the wave's profile begins to change. This friction slows the circular orbital motion of the wave's base, but the top continues at its original speed. In effect, the wave begins leaning forward on its approach to shore. When the wave's steepness ratio reaches 1:7, the wave's structure collapses on top of itself, forming a breaker. A spilling breaker is the classic rolling wave coming up a gradually sloping sandy beach. The long incline drains the energy of the wave over a large area. A plunging breaker approaches a steeper beachfront and forms a curling crest that moves over a pocket of air. The curling water is traveling faster

The classic curl of a breaking wave is associated worldwide with surfing. As a wave approaches shore, friction slows the bottom of the wave while allowing the top to continue moving, which causes the top to lean forward in this manner. than the slowing wave base, and the water outruns itself with nothing beneath for support. Along oceanfronts with steep inclines or cliffs, a wave's energy is expelled in a very short distance, often with great force. These surging breakers develop and break right at the shoreline, proving dangerous and sometimes fatal to unsuspecting beachgoers. The tremendous energy dissipated at the ocean-level interface results in enormous erosion and deposition. Reference: www.virtualnjshore.com/tbwaves.html

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How do waves move sand along a beach?

• Waves and currents move sand along a beach. • When waves hit the beach at an angle, they carry sand up and onto the shore in this direction. • The movement of waves that strike the shore at an angle is longshore current. • Once the waves have washed up, they are then pulled back by gravity. This causes a zigzag movement of sand (longshore drift). • This causes sand to move gradually down a beach. This causes sand to shrink in some areas and grow in others. Reference: www.cape.k12.mo.us/CJHS/science/gibbar/PowerPoints/ES/W...

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