Physical weathering can be defined as a process in which rocks are broken down into smaller pieces due to physical forces such as wind, gravity, water and other such processes that don’t change the chemical nature of the rock involved. Essentially the rocks are torn apart until they become sediment which is then carried along by erosion to be deposited either in lakebeds, streams, rivers or even the ocean itself until finally it becomes indistinguishable from its original form.
This process does not occur overnight rather it takes years of constant exposure to the elements before a rock formation starts to weather. For example rock formations called the “Pinnacles” in Nambung National Park in Australia were formed over thousands of years of constant battering from winds and rain which eventually caused the rock formations to become pinnacle shape.
Using such an example as a basis it can be determined that the current shape of most mountains, mountain ranges, hills, valleys and rock formations are all a result of constant physical weathering which changes the shape of the land over an extended period of time. Other processes besides wind and water involved in physical weathering are: the development of joints, frost wedging, heat, and finally animal and plant activities. Joints can be defined as spaced fractures in rocks that occur either through the cooling of rocks or a relief in the amount of pressure being applied on through the erosion of the rocks above them.
When joints form in rocks this allows agents of physical weathering to enter into the cracks further weakening it’s structure till finally the rock breaks into different pieces. Frost wedging refers to the process wherein water that has seeped into the different fractures of rocks starts to expand due to lowering temperatures. As the water starts to become ice it causes the cracks and gaps it has seeped into to considerably widen thereby weakening the overall structure of the rock.
While it is generally known that the regular heating and cooling of different rocks does not appear to cause any lasting damage exposure to sudden amounts of high heat have been known to warp rocks and cause them to break. Instances such as these happen during forest fires wherein due to the extreme temperatures involved the chemical composition of the rock may stay the same but heat actually causes the rock to expand and eventually break due to weakened structural bonds.
The last method of physical weathering is due to the activity of plants and animals for example plant roots tend to seep into cracks in rocks thereby expanding as they grow and cracking the rock in the process while animals on the other due to either burrowing or constant trampling can wear down the surface of most rocks due to their constant activity. In most cases of weathering it is the type of rock and the type of formation it has that influences the degree of weathering that happens to it.
For example limestone is a type of rock that is easily susceptible to the effects of physical weathering due to its weak composition not only that but rocks that are on the exposed surfaces of rock formations are more likely to be affected by erosion as compared to that of rock that is located deeper in the formation. This is due to the fact that the exposed surface of rock formations is in the direct path of most of the agents of weathering resulting in a greater likelihood of them being affected. The formation of the rock structure also plays an important factor in how it is weathered over time.
If a rock formation has a structure that juts out directly from the structure then it is this part that will directly be affected by weathering conditions as evidenced by earlier example of the “Pinnacles” in Nambung National Park in Australia. As such it can be said that physical weathering only occurs in instances where rock formations are in direct exposure to elements of erosions such as formations located on beaches, mountain ranges, deserts or streams and rivers, namely any location that has a constant flow of physical action that works against the surface of rocks.
In terms or rock stability physical weathering often causes rock formations that look spectacular as seen in America’s Death Valley, the Australian outback or in numerous other locations with unique rock formations unfortunately though these structures are physically fragile being kept together with weak bonds due to constant weathering that causes gaps in between rocks that is susceptible to collapsing in on itself due to the effects of gravity.
As such areas that are susceptible to weathering are areas where the rocks formations are not structurally sound and are likely to collapse eventually. When it comes to the effect of physical weathering on slides over time deposits from physical weathering can accumulate in certain locations such as on mountain slopes or on cliffs causing landslides when the ground becomes unstable however they are in relatively few areas and thus in most cases not a direct cause for concern.
Cases where it is a concern usually happen due to human interference, for example in a recent incident in the Philippines where a massive landslide came and killed hundreds of people because of the heavy rains that were affecting the area. The direct reason for the landslide was not the physical weathering of the area but rather the massive deforestation which caused the surrounding soil to become unstable causing the landslide. The time it takes to successfully weather down a substance all depends on the agents of weathering applied to it, the type of material and the rate of exposure.
For example a rock formation composed of hard igneous rock will take far longer to weather as compared formations composed of sedimentary rock due to the differences in composition with igneous rock formations having a structure that is more solid as compared to sedimentary rock. This evidenced by the fact that in most deserts where there are formations of sedimentary rock weathering from the wind has created interesting formation which are structurally weak as compared to dormant mountains where deposits from magma turned into igneous still retain a solid shape.
As such differences in composition means a different time frame involved in successfully eroding the material. Location also plays an important part in erosion significantly slowing or rapidly increasing the rate of erosion. In Australia for instance the 12 Apostles rock formation that are located near the Great Ocean road in Victoria are directly in the path of sea waves and wind coming from the ocean. As such the time frame in which they will be completely weathered away is greatly accelerated due to the constant exposure they experience.
Comparatively the Himalayan mountain range with relatively few agents of weathering has a significantly longer timeframe before they are weathered away due to the fact that they are located in an area where they aren’t exposed to as many agents of weathering as the 12 Apostles in Victoria, Australia. 2. In a lot of communities scattered around the world groundwater is an important resource that enabled them to survive. This is due to the fact that a lot of them don’t live near large sources of fresh water as such groundwater wells provide for nearly all of their daily water allowances.
In recent years groundwater aquifers have been affected by numerous outside influences that have turned this once plentiful and clean resource into dried soil and poisoned supplies of water. Ever since the middle of the 1900’s the global population has soared and as a result more and more people in areas far from lakes, rivers and streams have continuously sourced their water from groundwater aquifers. As such this has placed a strain on the resource since the amount of water originating from groundwater sources is determined by seasonal rainfall.
This results in times of either high or low levels of water supplies. With people indiscriminately sourcing massive amounts of water even during dry spells it is obvious that the source of the water will eventually feel the strain and at times be unable to meet the demands of the population sourcing the water. This has lead to water shortages in numerous areas due to overconsumption and as such people blame the government for the shortage when it is due to the indiscriminate consumption of water that there aquifers dried up in the first place.
Not only that but the popularity of golf in numerous areas means that in order to maintain these golf course millions of gallons of water are used on a daily basis in order to water the grass. Owners of these courses are willing to pay a premium on water supplies resulting in a preference for various water supplies to supply water to these golf courses instead of to communities resulting in an inevitable water shortage for those living in the area. Attempts to encourage water conservation are often met with derision since most people are under the assumption that water is a plentiful resource that can be obtained easily.
It is this assumption that has lead to vast misuses of groundwater sources resulting in water shortages for numerous communities who in the end suffer for their actions. The water table can be defined as a surface that divides the phreatic zone that is permanently saturated with water with that of the vadose zone in which the pore spaces that are not completely filled with water. From this it can be said that a water table can be said to be the upper surface of a body of groundwater that is in an area that is permanently saturated with water.
As such in bodies of groundwater the water table acts as the surface indicator of where pressure from the groundwater is roughly equivalent to that of atmospheric pressure. The relevance of this is that in cases of coastal areas where sea water and groundwater interact the sea water is usually displaced to an area below groundwater due to its heavier density. In instances where over drafting happens groundwater contamination occurs due to a lack of pressure and a combination of salt water and groundwater making the water in the aquifer undrinkable.
It isn’t just overdrawing that’s causing problems in groundwater management but also problems involving agricultural, urban groundwater and industrial pollution that’s causing problems in the water supply. In her book Silent Spring Rachel Carson mentions that when farmers use pesticides to prevent insects from eating their crops these pesticides have a tendency of mixing with water when the crops are irrigated and penetrate into the surrounding ground water causing the residents of nearby communities that draw water from these sources to be poisoned from pesticide residues found in the water.
Not only that but the indiscriminate disposal of chemicals by urban households such as detergents, soaps, floor cleaners and other chemicals into the surrounding environment have the potential of seeping into groundwater sources further contaminating them. Finally industrial factories that indiscriminately dispose of factory waste via drains leading out to the local environment are also guilty of poisoning ground water sources which has lead to numerous instances of sickness and even death in local communities surrounding these factories. 3.
The flowing water from steams and rivers is one of the dominant forces of erosion on the planet capable of shaping vast stretches of land and enriching river beds, lakes and seas with the nutrients it brings from the process of eroding sediment. The three process by which a river/stream is able to transport material is through erosion, transportation and the deposit of sediment. The first stage of the process is when water flows down from a downward slope originating from an elevated position such as mountain ranges or glaciers. As the water flows downwards it accumulates in small depression on the way down.
It is this accumulation of moving water that slowly starts to wear down the depression as more and more parts of it become sediment which flows along the rushing water. Large pieces of sediment are usually deposited downstream joining other pieces that have accumulated there over time. It is this action of depositing sediment and rushing water that slowly starts to wear down the larger pieces causing them to become silt. Silt cannot adhere to the bottom of the river as well as larger pieces of sediment as such it is easily carried even further downstream by the river.
It is during this process that the pieces of silt are slowly eroded away by rushing along with the water that they are no longer distinguishable from their original form. The final process involves the river reaching a large mass of water either a lake or the ocean and eventually depositing the now eroded silt on the lake or sea bed. It is this process or erosion, transportation and deposit that enables much needed minerals to reach large bodies of water thereby enriching the organism that live within it. When it comes to transporting materials in streams two important factors come into play: stream capacity and stream competence.
Stream capacity refers to the amount of total sediment that is present in a stream or river that a stream is capable of carrying while stream competence refers to the ability of a stream to transport an object of a particular size namely that of a boulder or pebble and other such object that are found in streams. These factors are important due to the fact that depending on stream competence and stream capacity different materials may be transported by the stream easily or may lead up to the stream creating a self made damn for itself due to the continuous deposit of materials that it can’t carry.
4. Mass movement can be defined as the downward movement of rocks, soil and debris under the influence of gravity. It occurs due to the weight of objects pressing down from above wherein the objects below cannot take the weight and the inevitable result is that the entire mass slides downward. Other causes can range from heavy rainfall, volcanic activity to earthquakes and man made changes to the environment such as deforestation which affects the compactness of the soil. The different types of mass movement are: soil creep, slide, slumps, solifluction, flows and rock falls.
Soil creep is characterized by an almost imperceptible appearance to the naked eye as such it is considered the slowest type of mass movement wherein the top few meters of soil moves due to contraction and expansion as a result of water in the ground that freezes and melts causing the soil to move as a result. A slide on the other hand happen as a result of a sheet of earth slides over and underlying weakened plane of earth which cannot handle the weight of the earth above it. Slide can end anywhere from a few meters to even a kilometer down a steep slope.
Slumps occur as a result of a backward rotation of material in the soil as it moves in curved failure plane which inevitably results in a reverse slope similar to that of a terrace. In fact Slumps can are unique due to the fact that they create a sort of stair like appearance in the soil as they form due to the downward sloping characteristic of the soil. Solifluction on the other hand while similar to the movement of a flow occurs only on permanently frosted surfaces such as those found in tundra in Northern Alaska.
When summer comes along and melts the upper levels of the frost the waterlogged soil slowly moves down the slope until it forms a sort of terrace over the land below. A flow can be described as a down slope movement of soil that has been saturated with water or that of weakened shale or loose clay layers. What happens is due to the loosened earth the entire top layer moves down however unlike mudslides a flow is relatively slow , is not confined to any sort of channel, are found more in humid areas than dry one and finally have a relatively low water content.
Mudflows are characterized by a sudden down slope movement of earth that is highly saturated with water. Certain conditions though have to met before mudflows are able to occur, for one thing the surface materials in that particular location have to be loose, secondly there must be a lot of steep slopes with a lot of water nearby and lastly very few obstacles such as trees and large boulders. One characteristic of mudflows is that they are more commonly found in dry areas where there is very little vegetation however with instances of flash floods due to heavy rains.
Also when mud flows move they tend to occupy channels for streams as they rush along due to the downward angle of the stream flow. The last type of mass movement are rock falls distinguished by their suddenness wherein large blocks of rock are shed all of a sudden from a mountain slide due to forces of weathering and gravity. Notable landslides, mudslides that have occurred recently are those that happened in the Philippines in the province of Leyte on October 2009.
Due to heavy rains that had bombarded the region the locals took shelter in their homes in order to escape the onslaught, what they didn’t know was that due to the massive deforestation that had happened in the region due to unscrupulous logging the surrounding topsoil had nothing to hold it in place. Combine that with record breaking rainfall and winds and the end result was a massive landslide that buried an entire village killing over 160 people. It must be noted though that while it is a tragedy it was their own fault because they didn’t take into account the consequences of unregulated logging in their area.
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