8/13/2019 What Are the Differences Between Desertification and Weathering

1/5

What are the differences between desertification and weathering,and also what are the benefits and the dangers from these two

processes?

The world's great deserts were formed by natural processes interacting overlong intervals of time. During most of these times, deserts have grown andshrunk independent of human activities. Paleodeserts, large sand seas nowinactive because they are stabilized by vegetation, extend well beyond thepresent margins of core deserts, such as the ahara. !n some regions, desertsare separated sharply from surrounding, less arid areas by mountains and othercontrasting landforms that reflect basic structural differences in the regionalgeology. !n other areas, desert fringes form a gradual transition from a dry to amore humid environment, making it more difficult to define the desert border.

These transition zones have very fragile, delicately balanced ecosystems.Desert fringes often are a mosaic of microclimates. mall hollows supportvegetation that picks up heat from the hot winds and protects the land from theprevailing winds. "fter rainfall the vegetated areas are distinctly cooler than thesurroundings. !n these marginal areas, human activity may stress the ecosystembeyond its tolerance limit, resulting in degradation of the land. #y pounding thesoil with their hooves, livestock compact the substrate, increase the proportion offine material, and reduce the percolation rate of the soil, thus encouragingerosion by wind and water. $razing and the collection of firewood reduces oreliminates plants that help to bind the soil.

This degradation of formerly productive land%% desertification%%is a complexprocess. !t involves multiple causes, and it proceeds at varying rates in differentclimates. Desertification may intensify a general climatic trend toward greateraridity, or it may initiate a change in local climate.

Desertification does not occur in linear, easily mappable patterns. Desertsadvance erratically, forming patches on their borders. "reas far from naturaldeserts can degrade &uickly to barren soil, rock, or sand through poor landmanagement. The presence of a nearby desert has no direct relationship todesertification. nfortunately, an area undergoing desertification is brought topublic attention only after the process is well underway. (ften little or no data areavailable to indicate the previous state of the ecosystem or the rate ofdegradation. cientists still &uestion whether desertification, as a process ofglobal change, is permanent or how and when it can be halted or reversed.

Desertification became well known in the )*+'s, when parts of the $reatPlains in the nited tates turned into the -Dust #owl- as a result of drought andpoor practices in farming, although the term itself was not used until almost )*.During the dust bowl period, millions of people were forced to abandon theirfarms and livelihoods. $reatly improved methods of agriculture and land andwater management in the $reat Plains have prevented that disaster from

8/13/2019 What Are the Differences Between Desertification and Weathering

2/5

recurring, but desertification presently affects millions of people in almost everycontinent.

!ncreased population and livestockpressure on marginal lands has

accelerated desertification. !n someareas, nomads moving to less arid areasdisrupt the local ecosystem and increasethe rate of erosion of the land. /omadsare trying to escape the desert, butbecause of their land%use practices, theyare bringing the desert with them.

!t is a misconception that droughts cause desertification. Droughts are commonin arid and semiarid lands. 0ell%managed lands can recover from drought whenthe rains return. 1ontinued land abuse during droughts, however, increases landdegradation. #y )*2+, the drought that began in )*34 in the ahel of 0est "fricaand the land%use practices there had caused the deaths of more than ),people and )5 million cattle, as well as the disruption of social organizations fromvillages to the national level.

0hile desertification has received tremendous publicity by the political andnews media, there are still many things that we don't know about the degradationof productive lands and the expansion of deserts. !n )*44 6idley /elson pointedout in an important scientific paper that the desertification problem and processesare not clearly defined. There is no consensus among researchers as to thespecific causes, extent, or degree of desertification. 1ontrary to many popularreports, desertification is actually a subtle and complex process of deteriorationthat may often be reversible.

!n the last 5 years, satellites have begun to provide the global monitoringnecessary for improving our understanding of desertification. 7andsat images of

the same area, taken several years apart but during the same point in thegrowing season, may indicate changes in the susceptibility of land todesertification. tudies using 7andsat data help demonstrate the impact ofpeople and animals on the 8arth. 9owever, other types of remote%sensingsystems, land%monitoring networks, and global data bases of field observationsare needed before the process and problems of desertification will be completelyunderstood.

7inear dunes of the ahara Desertencroach on /ouakchott, the capital of:auritania. The dunes border a

mos&ue at left ;photograph by $eorg$erster

8/13/2019 What Are the Differences Between Desertification and Weathering

3/5

"t the local level, individuals and governments can help to reclaim andprotect their lands. !n areas of sand dunes, covering the dunes with largeboulders or petroleum will interrupt the wind regime near the face of the dunesand prevent the sand from moving. and fences are used throughout the :iddle8ast and the nited tates, in the same way snow fences are used in the north.

Placement of straw grids, each up to a s&uare meter in area, will also decreasethe surface wind velocity. hrubs and trees planted within the grids are protectedby the straw until they take root. !n areas where some water is available forirrigation, shrubs planted on the lower one%third of a dune's windward side willstabilize the dune. This vegetation decreases the wind velocity near the base ofthe dune and prevents much of the sand from moving. 9igher velocity winds atthe top of the dune level it off and trees can be planted atop these flattenedsurfaces.

(ases and farmlands in windy regions can be protected by planting treefences or grass belts. and that manages to pass through the grass belts can be

caught in strips of trees planted as wind breaks to ) meters apart ad=acentto the belts. mall plots of trees may also be scattered inside oases to stabilizethe area. (n a much larger scale, a -$reen 0all,- which will eventually stretchmore than ,2 kilometers in length, much longer than the famous $reat 0all, isbeing planted in northeastern 1hina to protect -sandy lands-%%deserts believed tohave been created by human activity.

:ore efficient use of existing water resources and control of salinizationare other effective tools for improving arid lands. /ew ways are being sought touse surface%water resources such as rain water harvesting or irrigating withseasonal runoff from ad=acent highlands. /ew ways also being sought to find and

tap groundwater resources and to develop more effective ways of irrigating aridand semiarid lands. 6esearch on the reclamation of deserts also is focusing ondiscovering proper crop rotation to protect the fragile soil, on understanding howsand%fixing plants can be adapted to local environments, and on how grazinglands and water resources can be developed effectively without being overused.

!f we are to stop and reverse the degradation of arid and semiarid lands,we must understand how and why the rates of climate change, populationgrowth, and food production adversely affect these environments. The mosteffective intervention can come only from the wise use of the best earth%scienceinformation available.

The rocks, soil and other materials that make up the 8arth>s surface arealways changing due to the forces of weathering, erosion and deposition.0eathering is a natural process that breaks rocks into smaller and smallerpieces. 8rosion is a process that takes place when those pieces are carried awayfrom their original locations, and deposition occurs when the small rocks and soilend up in another area, helping to create new land. ometimes, as in rockslides,erosion and deposition happen &uickly. :ore often than not, weathering and

8/13/2019 What Are the Differences Between Desertification and Weathering

4/5

erosion happens so slowly that you can>t even see it. ?orces like wind, snow andrain are responsible for the physical weathering of rocks, causing them to beworn down, cracked or broken into smaller pieces. 0ind picks up sand and otherparticles, blowing them against rocks, buildings, statues and other surfaces.0aves crashing against rocks at the shoreline wear away those rocks, turning

rock particles into sand. !n fast flowing streams, rocks tumble against each other,smoothing and rounding out rough surfaces. These are all examples of abrasion.Temperature changes, especially from day to night, also cause physical

weathering. The cold of night causes rocks to shrink or contract. !n daylight, thesun heats and expands the outer layers of rock while the insides are still cold.This temperature difference causes outer layers of rock to flake off. #ecausewater expands when frozen, water that seeps into cracks on rocks> surfaces canfreeze and cause rocks to split open. "nimals and plants can also cause physicalweathering. "nimals that burrow into the ground, digging their homes under andbetween rocks, are unknowingly responsible for exposing those rock surfaces towind, water and temperature changes. 7ike the splitting of rocks by freezing

water, the pressure of growing plant roots that have moved into cracks and holesin rocks cause them to split open as well. 6ocks are also changed through theprocess of chemical weathering. 1hemical weathering can occur when certainchemicals called acids dissolve rocks and change them into new substances.:any of the minerals that make up rocks will slowly dissolve as the weak acidsfound in water react with the rocks. This type of weathering can be seen in themany interesting rock formations often found in limestone caves. The water thatslowly soaks and drips into the cave changes the rocks over many years. omeplants also give off weak acids that can dissolve or change rock surfaces. (nceweathering breaks down land, the process of erosion carries rocks and soil away,while the process of deposition helps create new land somewhere else. :any of

the same forces that cause weathering, such as wind, running water, waves andice, can also carry away rocks and deposit them elsewhere. 0ind picks up andcarries dust, sand and other things. 0hen the wind stops, these fragments fall tothe ground in new locations. During heavy rains, when the soil can hold no morewater, the excess water called runoff carries away topsoil that is not protected byplants. 9eavy runoff can create streams that wear away the land. "s streamsflow into rivers, the soil, sand and rocks carried by the water are deposited alongthe sides and at the mouth of rivers.

"lthough weathering, erosion and deposition cause some problems forpeople, these natural processes also have benefits. ?or example, while topsoil iswashed or blown away by wind and rain, rich new land that is good for growingcrops is deposited along shores and at river deltas. (cean waves weather anderode rocks, but the sand that is deposited on shorelines often protects homesalong the shore from damage by storms. $laciers gouge out huge mountainvalleys, and they are also responsible for creating thousands of lakes frommelting blocks of ice. "s these large sheets of ice move over the 8arth, theycarry soil and rocks and deposit them in new places, creating new land

8/13/2019 What Are the Differences Between Desertification and Weathering

5/5

formations. nderstanding the ongoing natural cycle of weathering, erosion anddeposition helps us understand our changing 8arth.