Explain any two landforms created due to the transportation function of river with suitable diagrams.
Answers
If you've ever been in a sand storm, you've felt the power of the wind carrying sand particles and blasting at your skin. Over time, this natural sand blasting can be a tremendous erosional force on rocks or buildings. Hopefully, you won't stay out long enough to experience permanent damage.
Transport of Particles by Wind
Wind transports small particles, such as silt and clay, over great distances, even halfway across a continent or an entire ocean basin. Particles may be suspended for days. Wind more easily picks up particles on ground that has been disturbed, such as a construction site or a sand dune. Just like flowing water, wind transports particles as both bed load and suspended load. For wind, bed load is made of sand-sized particles, many of which move by saltation . The suspended load is very small particles of silt and clay.
Diagram of how wind can transport particles, and a picture of a dust storm
Wind transport is by suspension, saltation, and creep (bed load). In a sandstorm, sand is usually within a meter of the ground. A dust storm's smaller particles can travel higher. A dust storm as it approaches Al Asad, Iraq
Wind Erosion
Wind is a stronger erosional force in arid regions than it is in humid regions because winds are stronger. In humid areas, water and vegetation bind the soil so it is harder to pick up. In arid regions, small particles are selectively picked up and transported.
Deflation
As small particles are removed, the ground surface gets lower and rockier, causing deflation. What is left is desert pavement , a surface covered by gravel-sized particles that are not easily moved by wind.
Desert pavement formed as a result of deflation
This desert pavement formed in the Mojave Desert as a result of deflation.
Abrasion
Particles moved by wind do the work of abrasion. As a grain strikes another grain or surface it erodes that surface. Abrasion by wind may polish natural or human-made surfaces, such as buildings. Stones that have become polished and faceted due to abrasion by sand particles are called ventifacts
A ventifact formed by wind abrasion
As wind blows from different direction, polished flat surfaces create a ventifact.
Desert Varnish
Exposed rocks in desert areas often develop a dark brown or black coating called desert varnish. Wind transports clay-sized particles that chemically react with other substances at high temperatures. The coating is formed of iron and manganese oxides .
Petroglyphs carved into desert varnish
Ancient people carved these petroglyphs into desert varnish near Canyonlands National Park in Utah.
Wind Deposition
The main features deposited by wind are sand dunes. Loess are wind deposits of finer sediments.
Sand Dunes
Deserts and seashores sometimes have sand dunes . Beach dunes are usually made of quartz because quartz is what's left in humid areas as other minerals weather into clays. Sand dunes may be composed of calcium carbonate in tropical areas. But in deserts, sand dunes are composed of a variety of minerals because there is little weathering.
Dune sands are usually very uniform in size and shape. Larger particles are too heavy for the wind to transport by suspension and smaller particles can't be picked up. Particles are rounded, since rounded grains roll more easily than angular grains.
Sand dunes in Death Valley
This sand dune in Death Valley, California shows secondary sand ripples along its slip face.
For sand dunes to form there must be an abundant supply of sand and steady winds. A strong wind slows down, often over some type of obstacle, such as a rock or some vegetation, and drops its sand. As the wind moves up and over the obstacle, it increases in speed. It carries the sand grains up the gently sloping, upwind side of the dune by saltation. As the wind passes over the dune, its speed decreases. Sand cascades down the crest, forming the slip face of the dune. The slip face is steep because it is at the angle of repose for dry sand, about 34o (Figure below).
How a sand dune forms
Sand dunes slope gently in the upwind direction. Downwind, a steeper slip face forms.
Wind deposits dune sands layer by layer. If the wind changes directions, cross beds form. Cross beds are named for the way each layer is formed at an angle to the ground