Landforms By Wind: Geological Work Of Wind Dr. Prabha Joshi Department: B.E. Civil Engineering Subject: Engineering Geology Semester: III Teaching Aids Service by KRRC Information Section Teaching Aids Service by KRRC Information Section

Geological work of wind Air in motion is called Wind. Wind is an effective agent of erosion, transportation and deposition in desert regions. Wind also moves loose sediment in a variety of other Environments.

Wind Erosion Deflation Deflation: Latin- deflare= to blow away. Removal of particles of dust and sand by winds, this is the main process of erosion in deserts Low spots carved out by wind erosion High elevations are left due to vegetative stabilization

Blowouts and Oasis Deflation may cause removal of sand from a particular location to such an extent that a big depression is created. Sometimes these depressions intersect the water table and get partially filled up with water and called oasis.

Yardangs These are elongated low-lying ridges forming overhang above local depressions. The trend is parallel to prevailing winds. They commonly occur in groups. Form in areas of alternating hard and soft rocks.

Pedestal or Mushroom rock Base of a rock is weathered and eroded more quickly due to sand blasting Sand grains can only be picked up a couple of feet

Natural arch Typically formed by a combination of wind and water Narrow ridges are formed and the softer substrata is weathered first, forming a bridge/arch overhead

Arches National Park, Utah

Ventifact These are small rock fragments created by wind erosion, showing one, two or more wind polished surfaces. Wind carries fine particles that work like a sand blaster (i.e. silt, clay, and ice particles) The windward face of the rock is flattened and smoothed Usually pebble to cobble sized

Dreikanter A type of ventifact that has three ridges Multiple faces have been formed by either a changing prevailing wind or movement of the actual rock being weathered

Desert pavement or Hammada It is the Bare rock surface in a desert formed when wind carries finer, more lightweight particles such as sand away Large particles are left behind and protect from further erosion

How does Wind transport sediment? Saltation • Sediments too large or heavy to be carried in suspension by water or wind are dropped and picked up again and again during transportation process. It is therefore a process of sediment transport in series of jumps. Suspension Silt- and clay sized particles constitute most of this load, held aloft for many miles

Deposition by Wind Loess: Loess is unconsolidated, unstratified and porous accumulation of yellowish, fine grained silt and clay sized particles. Formed by glaciers. Carried and deposited by wind.

Loess is a deposition of silt, with a little amount of sand and clay Loess is a deposition of silt, with a little amount of sand and clay. It appears yellowish or brownish in color. Many a times, wind action is responsible for formation of loess. Glacial activities also contribute to formation of a loess.

Sand Dunes Variously shaped deposits of sand grade particles. Deposited by wind Leeward side (slip face) has a steeper slope Windward side is more gradual Leeward Windward

Barchan Dune Crescent shaped dunes Concave side is the leeward side Formed from a unidirectional wind cusp crest

Dunes

Transverse dunes A dune that elongates perpendicular to the prevailing wind Caused by a combination of wind directions

Longitudinal (Seif) dunes Longitudinal dunes (also called Seif dunes, after the Arabic word for "sword"), elongate parallel to the prevailing wind. Seif dunes are sharp-crested and are common in the Sahara. A seif dune is a steep sided ridge that extend in a sinuous or s-shaped outline. Both the sides of a sigmoidal dune are steeply inclined at angles of 25-300.

Parabolic dunes Crescent shaped dunes Concave side is the windward side Found in coastal deserts Arms of the crescent lag behind because they are held in place by vegetation

Ergs Huge dune fields

Ripple marks Miniature dunes within a dune (not more than 2 inches tall) Formed by wind May form from cross winds and appear to be traveling in a different direction than the large dune

Sunlight casts shadows on sand dunes in White Sands National Monument, New Mexico. These dunes are made of pure gypsum, a soft mineral left behind when water evaporates from a nearby lake.

Three motorcyclists drive around rock formations in Zion National Park, Utah. The rock formations are actually ancient sand dunes. Weathering from wind and water will eventually turn Zion's rock formations to sediment and dust again.

An aerial photo captures sand dunes under shallow water near the Bahamas, in the Caribbean Sea. These dunes are created by water currents. Wind currents form sand dunes on land.

Sand dunes form on ancient salt beds in Baja California, Mexico Sand dunes form on ancient salt beds in Baja California, Mexico. Wind erosion moves the sand dunes across the landscape. The curving dunes "point" the way the wind is blowing.