{"id":1322,"date":"2026-05-12T20:28:51","date_gmt":"2026-05-12T20:28:51","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/accphysicalgeology\/?post_type=chapter&p=1322"},"modified":"2026-05-28T22:42:39","modified_gmt":"2026-05-28T22:42:39","slug":"23-3-erosion-in-deserts-physical-geology-2nd-edition","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/accphysicalgeology\/chapter\/23-3-erosion-in-deserts-physical-geology-2nd-edition\/","title":{"raw":"23.3 Erosion in Deserts — Physical Geology – 2nd Edition","rendered":"23.3 Erosion in Deserts — Physical Geology – 2nd Edition"},"content":{"raw":"

23.3 Erosional Features of Deserts<\/h1>\r\nIf one stands in a desert somewhere in the American Southwest, one would probably see a bunch of rocks and sand, but probably not too much in the way of \"conventional\" brown soil (Figure 23.3.1). Indeed, soils do form in deserts but are of a very different set of characteristics. Furthermore, if one looks at rocky cliffs, fractured rock and slopes littered with loose boulders are commonplace. Thus, weathering and erosion do take place in deserts but in different forms than in more temperate areas.\r\n

Soil Development<\/h4>\r\nSince there is a relative lack of organic content in deserts, most soils lack an O and an A layer (or they are extremely thin). Thus, in most desert floors, you would walk directly on the E layer (Figure 23.3.1). With the lack of organic content, desert soils are largely characterized by their inorganic mineral content, which is reflected in the bedrock color of the area. With the high oxygen exposure in deserts, hues of red are commonly seen, reflective of the iron content. Specifically, hues of red, brown, orange and yellow reflect oxidized iron (Fe+3<\/sup> ions), whereas shades of white and green indicate reduced iron (Fe +2<\/sup>) ions (Figure 23.3.2).\r\n\r\n\r\n\r\nFigure 23.3.1. A representation of typical desert soil found in the Mojave Desert. Note the sand-sized dominantly quartz grains and lack of organic matter.\r\n\r\n\"File:CalhanFigure 23.3.2a (left) The Painted Desert in northern Arizona, and b) (right) The Paint Mines in Calhan, CO. Both locales show a dazzling array of red, pink, and yellow hues, all characterized by varying degrees of oxidation of Fe+3<\/sup> bearing sedimentary rock.\r\n\r\n \r\n\r\nA common sighting in deserts is a chalky white surface that can resemble salt, but is actually caliche<\/strong>. Since rainfall is rare, the degree of moisture infiltration into the subsurface is limited. Thus, the \"washing\" of ions from the surface to the underground does not progress very far. Aqueous calcium tends to re-precipitate to form a calcite cement that binds any loose soil, which is the caliche (Figure 23.3.3).\r\n\r\n\r\n\r\nFigure 23.3.3. A mound of caliche rock in central Texas.\r\n

Key Erosional Landforms<\/h4>\r\nWhen one thinks of currents of movement in deserts, wind<\/em> is probably the preeminent example that comes to mind (especially wind-blown sand). Instead of hues of red, orange, or yellow, a desert-goer might come across some rock surfaces that are colored a shiny very dark brown to almost black. This is known as desert varnish<\/strong>. Here, wind blown dust particles can get stuck on a surface. Microbes that are amongst the dust extract metal ions, such as iron and manganese, and oxidize them, which act as a cement. Not only does the varnish take a very long time to form, but it is exclusive to deserts since high humidity would wash the material away. Thus, if one were to measure the thickness of desert varnish at a location, it is a great indicate as to how long the desert has been around. With ancient cultures, such as Native Americans, they have learned to chip and carve into the varnish to create symbols and expressive figures known as petroglyphs <\/strong>(Figure 23.3.4).<\/strong>\r\n\r\n\r\n\r\nFigure 23.3.4. An array of petroglyphs carved in desert varnish, Nine-Mile Canyon, eastern Utah.\r\n\r\nSince vegetative cover is relatively low in deserts, particles are more easily moved without the anchoring effect of plants. As such, particularly strong winds can easily create dust storms, <\/strong>which can topple 1.5 kilometers in height (Figure 23.3.5). From a distance, these storms are easily visible as they resemble rolling, opaque clouds. Since quartz is the dominant mineral in sand, fast-moving quartz can create numerous issues due to its high hardness, such as: stripping paint off of vehicles and buildings, cause breathing issues, and frosting glass surfaces. In addition, wind-blown sand is effective at carving and polishing rock faces. Loose rocks that have been wind-polished, or abraded, on multiple sides are known as ventifacts <\/strong>(Figure 23.3.6.). If the same action takes place at extensive rock outcrops, the wind-polished outcrops are known as yardangs<\/strong>.\r\n\r\n \r\n\r\nFigure 23.3.5. (left) A dust storm in progress in the Black Rock Desert of Nevada. Figure 23.3.6. (right) A sand-blown ventifact in the Mojave Desert in California.\r\n\r\n \r\n\r\nIn areas where there is both a variety of sediment sizes and strong winds, the wind erodes the soft and small sediment leaving behind the larger particles. This results in physical land lowering over time with a process called deflation <\/strong>(Figure 23.3.7.). In areas with especially sparse vegetation, this process can hasten.\r\n\r\n\"File:Desert\r\n\r\nFigure 23.3.7. Desert deflation resulting from finer sediments being blown away leaving behind a high concentration of large clasts.\r\n\r\nAlthough wind is the apparent erosional agent in deserts, do not underestimate the power of water erosion when it is present! Since the desert floor is often very hard, any amount of precipitation that touches down (even seemingly small amounts) is often prone to ponding on the surface as runoff<\/em> very quickly. This allows the water to radically carve the landscape in hours to even minutes! When surface runoff is channeled in downslope areas, dry washes<\/strong> often result. During the majority of the time, these channels are ephemeral (bone dry) but \"reactivate\" during periods of intense precipitation (Figure 23.3.8.).\r\n\r\n\r\n\r\nFigure 23.3.8. A dry wash in southern Arizona. Note the row of vegetation on either sides serving as the \"banks\" of this dry channel.\r\n\r\nThe next series of erosional landforms form in a sequence, of sorts. Due to the relative lack of soil, deserts often have cliffs and ridges composed of solid rock. If we start with a broad, flat rocky surface with cliffs, erosion will naturally chip away at the cliffs over time. This results in two features: 1) a talus slope<\/strong> of rocky rubble at the cliff bottom (review weathering - chapter 5), and 2) cliff retreat<\/strong> wherein the position of the cliff moves. The overall shape and slope of the cliff is roughly the same, but cliff retreat decreases the area of flat ground at the top. The more extensive areas of flat tops bound by cliffs are termed plateaus<\/strong>, medium size flat areas are called mesas<\/strong> (Spanish for \"table<\/em>\"), with smaller ones being termed buttes <\/strong>(Figure 23.3.9.). This sequence of landforms occur when the sedimentary rock strata or horizontal (the cliff faces form by vertical joints). If a sequence of rock strata is tilted, and is composed of layers of alternating resistances to weathering, a cuestra<\/strong> forms.\r\n\r\n\r\n\r\nFigure 23.3.9. Plateaus, mesas and buttes are all seen from this panoramic view in Canyonlands National Park, southern Utah.\r\n\r\nThe last series of landforms starts with a vertical joint, or a crack, that is exposed at the surface. A combination of wind, water and ice erosion can propagate the crack further downward and widen it. If there are a series of adjoining cracks separated by a thin lip of rock, the lip of rock extending downward is a fin<\/strong> (or wall) that separates neighboring slot canyons <\/strong>(Figure 23.3.10a). If erosion cannot progress further downward, then the next best direction of erosion will be horizontally (or laterally). This will then attack the center part of the fins where eventually a hole develops termed windows<\/strong> (think of taking a giant hole puncher through a parallel series of fins like they were a stack of paper). If the window propagates further, then arches<\/strong> can form (like those in the world-renowned Arches National Park in southern Utah!) (Figure 23.2.10b). Lastly, if arches continue to erode, then the top (apex) material will have no more underlying support that the arches collapse into chimneys<\/strong> (where only the \"legs\" of the once-arches are left standing).\r\n\r\n \r\n\r\nFigure 23.3.10a (left) A series of parallel fins and adjoining slot canyons at Arches National Park, southern Utah. Figure 23.3.10b (right) One of many notable arches at Arches National Park.\r\n

Media Attributions<\/h3>\r\n
    \r\n \t
  • Figures 23.3.1 - 23.3.10: Wikimedia Commons<\/li>\r\n<\/ul>","rendered":"

    23.3 Erosional Features of Deserts<\/h1>\n

    If one stands in a desert somewhere in the American Southwest, one would probably see a bunch of rocks and sand, but probably not too much in the way of “conventional” brown soil (Figure 23.3.1). Indeed, soils do form in deserts but are of a very different set of characteristics. Furthermore, if one looks at rocky cliffs, fractured rock and slopes littered with loose boulders are commonplace. Thus, weathering and erosion do take place in deserts but in different forms than in more temperate areas.<\/p>\n

    Soil Development<\/h4>\n

    Since there is a relative lack of organic content in deserts, most soils lack an O and an A layer (or they are extremely thin). Thus, in most desert floors, you would walk directly on the E layer (Figure 23.3.1). With the lack of organic content, desert soils are largely characterized by their inorganic mineral content, which is reflected in the bedrock color of the area. With the high oxygen exposure in deserts, hues of red are commonly seen, reflective of the iron content. Specifically, hues of red, brown, orange and yellow reflect oxidized iron (Fe+3<\/sup> ions), whereas shades of white and green indicate reduced iron (Fe +2<\/sup>) ions (Figure 23.3.2).<\/p>\n

    \"image\"<\/p>\n

    Figure 23.3.1. A representation of typical desert soil found in the Mojave Desert. Note the sand-sized dominantly quartz grains and lack of organic matter.<\/p>\n

    \"image\"\"File:CalhanFigure 23.3.2a (left) The Painted Desert in northern Arizona, and b) (right) The Paint Mines in Calhan, CO. Both locales show a dazzling array of red, pink, and yellow hues, all characterized by varying degrees of oxidation of Fe+3<\/sup> bearing sedimentary rock.<\/p>\n

     <\/p>\n

    A common sighting in deserts is a chalky white surface that can resemble salt, but is actually caliche<\/strong>. Since rainfall is rare, the degree of moisture infiltration into the subsurface is limited. Thus, the “washing” of ions from the surface to the underground does not progress very far. Aqueous calcium tends to re-precipitate to form a calcite cement that binds any loose soil, which is the caliche (Figure 23.3.3).<\/p>\n

    \"image\"<\/p>\n

    Figure 23.3.3. A mound of caliche rock in central Texas.<\/p>\n

    Key Erosional Landforms<\/h4>\n

    When one thinks of currents of movement in deserts, wind<\/em> is probably the preeminent example that comes to mind (especially wind-blown sand). Instead of hues of red, orange, or yellow, a desert-goer might come across some rock surfaces that are colored a shiny very dark brown to almost black. This is known as desert varnish<\/strong>. Here, wind blown dust particles can get stuck on a surface. Microbes that are amongst the dust extract metal ions, such as iron and manganese, and oxidize them, which act as a cement. Not only does the varnish take a very long time to form, but it is exclusive to deserts since high humidity would wash the material away. Thus, if one were to measure the thickness of desert varnish at a location, it is a great indicate as to how long the desert has been around. With ancient cultures, such as Native Americans, they have learned to chip and carve into the varnish to create symbols and expressive figures known as petroglyphs <\/strong>(Figure 23.3.4).<\/strong><\/p>\n

    \"image\"<\/p>\n

    Figure 23.3.4. An array of petroglyphs carved in desert varnish, Nine-Mile Canyon, eastern Utah.<\/p>\n

    Since vegetative cover is relatively low in deserts, particles are more easily moved without the anchoring effect of plants. As such, particularly strong winds can easily create dust storms, <\/strong>which can topple 1.5 kilometers in height (Figure 23.3.5). From a distance, these storms are easily visible as they resemble rolling, opaque clouds. Since quartz is the dominant mineral in sand, fast-moving quartz can create numerous issues due to its high hardness, such as: stripping paint off of vehicles and buildings, cause breathing issues, and frosting glass surfaces. In addition, wind-blown sand is effective at carving and polishing rock faces. Loose rocks that have been wind-polished, or abraded, on multiple sides are known as ventifacts <\/strong>(Figure 23.3.6.). If the same action takes place at extensive rock outcrops, the wind-polished outcrops are known as yardangs<\/strong>.<\/p>\n

    \"image\" \"image\"<\/p>\n

    Figure 23.3.5. (left) A dust storm in progress in the Black Rock Desert of Nevada. Figure 23.3.6. (right) A sand-blown ventifact in the Mojave Desert in California.<\/p>\n

     <\/p>\n

    In areas where there is both a variety of sediment sizes and strong winds, the wind erodes the soft and small sediment leaving behind the larger particles. This results in physical land lowering over time with a process called deflation <\/strong>(Figure 23.3.7.). In areas with especially sparse vegetation, this process can hasten.<\/p>\n

    \"File:Desert<\/p>\n

    Figure 23.3.7. Desert deflation resulting from finer sediments being blown away leaving behind a high concentration of large clasts.<\/p>\n

    Although wind is the apparent erosional agent in deserts, do not underestimate the power of water erosion when it is present! Since the desert floor is often very hard, any amount of precipitation that touches down (even seemingly small amounts) is often prone to ponding on the surface as runoff<\/em> very quickly. This allows the water to radically carve the landscape in hours to even minutes! When surface runoff is channeled in downslope areas, dry washes<\/strong> often result. During the majority of the time, these channels are ephemeral (bone dry) but “reactivate” during periods of intense precipitation (Figure 23.3.8.).<\/p>\n

    \"image\"<\/p>\n

    Figure 23.3.8. A dry wash in southern Arizona. Note the row of vegetation on either sides serving as the “banks” of this dry channel.<\/p>\n

    The next series of erosional landforms form in a sequence, of sorts. Due to the relative lack of soil, deserts often have cliffs and ridges composed of solid rock. If we start with a broad, flat rocky surface with cliffs, erosion will naturally chip away at the cliffs over time. This results in two features: 1) a talus slope<\/strong> of rocky rubble at the cliff bottom (review weathering – chapter 5), and 2) cliff retreat<\/strong> wherein the position of the cliff moves. The overall shape and slope of the cliff is roughly the same, but cliff retreat decreases the area of flat ground at the top. The more extensive areas of flat tops bound by cliffs are termed plateaus<\/strong>, medium size flat areas are called mesas<\/strong> (Spanish for “table<\/em>“), with smaller ones being termed buttes <\/strong>(Figure 23.3.9.). This sequence of landforms occur when the sedimentary rock strata or horizontal (the cliff faces form by vertical joints). If a sequence of rock strata is tilted, and is composed of layers of alternating resistances to weathering, a cuestra<\/strong> forms.<\/p>\n

    \"image\"<\/p>\n

    Figure 23.3.9. Plateaus, mesas and buttes are all seen from this panoramic view in Canyonlands National Park, southern Utah.<\/p>\n

    The last series of landforms starts with a vertical joint, or a crack, that is exposed at the surface. A combination of wind, water and ice erosion can propagate the crack further downward and widen it. If there are a series of adjoining cracks separated by a thin lip of rock, the lip of rock extending downward is a fin<\/strong> (or wall) that separates neighboring slot canyons <\/strong>(Figure 23.3.10a). If erosion cannot progress further downward, then the next best direction of erosion will be horizontally (or laterally). This will then attack the center part of the fins where eventually a hole develops termed windows<\/strong> (think of taking a giant hole puncher through a parallel series of fins like they were a stack of paper). If the window propagates further, then arches<\/strong> can form (like those in the world-renowned Arches National Park in southern Utah!) (Figure 23.2.10b). Lastly, if arches continue to erode, then the top (apex) material will have no more underlying support that the arches collapse into chimneys<\/strong> (where only the “legs” of the once-arches are left standing).<\/p>\n

    \"image\" \"image\"<\/p>\n

    Figure 23.3.10a (left) A series of parallel fins and adjoining slot canyons at Arches National Park, southern Utah. Figure 23.3.10b (right) One of many notable arches at Arches National Park.<\/p>\n

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