Formation and Characteristics of Deserts
Concept Map
The main topic of the text is the formation and characteristics of desert landforms such as sand sheets, sand dunes, and gypsum dune fields, along with the adaptations of desert ecosystems. It details how wind shapes these features and the survival strategies of flora and fauna in arid conditions. The text also touches on erosional landforms and phenomena like hamadas, reg, and dust storms.
Summary
Outline
Formation and Characteristics of Sand Sheets
Sand sheets are extensive, nearly level expanses of land covered by sand and fine sediments, often found in desert environments. These features are formed by the deposition of windblown particles, creating a layer that can vary in thickness from a few centimeters to several meters. The structure of sand sheets is layered, with horizontal strata of coarse silt and fine to medium sand, interspersed with thin layers of coarser sand and pea-sized gravel. These larger particles help to stabilize the finer grains and can lead to the formation of desert pavement, where stones are compacted on the surface. Wind speeds exceeding 24 kilometers per hour can generate small, temporary ripples on the sand sheets, which are aligned perpendicular to the wind direction and change with variations in wind patterns.The Formation and Migration of Sand Dunes
Sand dunes are dynamic landforms created by the wind's ability to transport and deposit sand, often forming mounds or ridges downwind from sources of loose sand. The development of dunes is driven by saltation, where sand grains bounce along the ground, and creep, where they roll or slide. The windward side of a dune typically has a gentler slope, while the leeward side is steeper, at the angle of repose for dry sand. Dunes are not static; they migrate over time as sand is continuously moved from the windward to the leeward side. Dune fields, or ergs, consist of numerous dunes, and their shapes—such as barchan, seif, transverse, star, and dome dunes—are determined by prevailing wind conditions and the availability of sand.Gypsum Dune Fields and Desert Pavement Formation
Unique gypsum dune fields, like those in White Sands National Park, New Mexico, are formed from the evaporation of mineral-rich water in closed basins, leaving behind gypsum crystals. These crystals are then broken down by wind erosion, creating the characteristic white dunes. Desert pavement is another desert feature, consisting of a surface layer of closely packed stones. This forms when wind erosion removes smaller particles, leaving a layer of larger rocks. The exact process of desert pavement formation is complex and not entirely understood, but it results in a stable surface that is resistant to further erosion.Desert Ecosystems: Adaptation to Aridity
Desert and semi-desert ecosystems are adapted to the extreme conditions of arid and semi-arid climates, often located in subtropical high-pressure zones or in the rain shadows of large landmasses. These ecosystems are characterized by low biomass and primary productivity, with vegetation and animal populations that have adapted to the scarcity of water. Desert flora and fauna exhibit a range of survival strategies, including water conservation, heat avoidance, and opportunistic breeding following rainfall events, allowing them to thrive in these challenging environments.Plant Adaptations in Desert Environments
Desert plants have evolved a variety of adaptations to cope with water scarcity, extreme temperatures, and herbivory. Many employ crassulacean acid metabolism, opening their stomata at night to reduce water loss. Some have reduced or absent leaves to minimize transpiration, while others store water in succulent leaves or stems. Cacti, for example, have adapted to store water in their trunks and have specialized cellular structures to support this function. Desert plants may also have extensive shallow roots or deep taproots to access water, and some species, like the saltbush, are adapted to saline conditions. Protective features such as spines help deter herbivores and protect the plant's water supply.Erosional Landforms and Phenomena in Deserts
Deserts feature a variety of landforms shaped by wind and water erosion, including hamadas—rocky plateaus stripped of sand—and gravel-covered plains known as reg, serir, and gibber. Erosional processes can also create dramatic landscapes, such as the eroded sandstone formations of the Tassili Plateau and the deep canyons of the Colorado Plateau. Deserts are also prone to dust and sandstorms, where wind lifts fine particles or heavier sand grains into the air, reducing visibility and sometimes causing electrical disturbances due to the charged nature of the particles. These phenomena are integral to the dynamic nature of desert environments.
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Sand Sheets
Formation
Sand sheets are formed by the deposition of windblown particles, creating a layered structure of sand and fine sediments
Characteristics
Structure
Sand sheets have a layered structure of coarse silt and fine to medium sand, interspersed with thin layers of coarser sand and pea-sized gravel
Wind Patterns
Wind speeds exceeding 24 kilometers per hour can generate small, temporary ripples on the sand sheets, which are aligned perpendicular to the wind direction and change with variations in wind patterns
Desert Pavement
The larger particles in sand sheets can lead to the formation of desert pavement, where stones are compacted on the surface
Sand Dunes
Formation and Migration
Sand dunes are dynamic landforms created by the wind's ability to transport and deposit sand, often forming mounds or ridges downwind from sources of loose sand
Structure
Windward and Leeward Sides
The windward side of a dune typically has a gentler slope, while the leeward side is steeper, at the angle of repose for dry sand
Dune Fields
Dune fields, or ergs, consist of numerous dunes, and their shapes are determined by prevailing wind conditions and the availability of sand
Gypsum Dune Fields and Desert Pavement Formation
Formation
Unique gypsum dune fields, like those in White Sands National Park, New Mexico, are formed from the evaporation of mineral-rich water in closed basins, leaving behind gypsum crystals
Desert Pavement
Desert pavement is formed when wind erosion removes smaller particles, leaving a layer of larger rocks, resulting in a stable surface that is resistant to further erosion
Desert Ecosystems and Adaptations
Adaptation to Aridity
Desert and semi-desert ecosystems are adapted to the extreme conditions of arid and semi-arid climates, with vegetation and animal populations that have adapted to the scarcity of water
Plant Adaptations
Water Conservation
Desert plants have evolved a variety of adaptations, such as crassulacean acid metabolism, to conserve water in arid environments
Heat Avoidance
Some desert plants have reduced or absent leaves to minimize transpiration and protect against extreme temperatures
Water Storage
Other desert plants, like cacti, have adapted to store water in their trunks and have specialized cellular structures to support this function
Animal Adaptations
Water Conservation
Desert animals have adapted to conserve water through behaviors such as burrowing or nocturnal activity
Heat Avoidance
Some desert animals have physical adaptations, such as light-colored fur, to reflect heat and stay cool in hot environments
Opportunistic Breeding
Desert animals may breed opportunistically following rainfall events, taking advantage of temporary water sources in arid environments
Formation and Characteristics of Deserts
Learn with Algor Education flashcards
Click on each Card to learn more about the topic
00
The composition of sand sheets includes horizontal layers of ______ and sand, with occasional ______ and gravel.
coarse silt
coarser sand
01
When wind speeds surpass ______ per hour, they can create ______ on sand sheets, which shift with the wind.
24 kilometers
temporary ripples
02
Dune Migration Process
Dunes migrate as wind moves sand from windward to leeward side, reshaping the dune.
