18 Questions
What is the term used for shallow depressions in deserts caused by wind erosion?
Blowouts
Which desert landform is described as a flat-topped mountain?
Table
What is the term for the process of lifting and removing fine sediments like clay and silt by wind?
Deflation
In deserts, what type of sediments are rolled or skipped by the wind, known as saltation?
Sand-sized
When water loses its competence and deposits sediments at the base of mountains, what landform is created?
Alluvial fan
'Yardang' landforms in deserts are described as:
Streamlined wind-sculpted bedrock pieces
What is the principal type of weathering in deserts due to the lack of moisture?
Mechanical weathering
In hot deserts, what process causes minerals to break down by expanding and contracting unequally?
Frost-wedging
What is the main source of water in deserts according to the text?
Water coming from outside the desert
Which type of soil is typically found in deserts, characterized by being high in mineral matter and low in organic matter?
Sandy soil
In deserts, which form of water erosion does the most erosional work, even though it may be infrequent?
Ephemeral Streams erosion
What process in hot deserts involves wind picking up fine sediments and using them as an abrasive to solid rocks?
Sand blasting
What is the ultimate lowest point to which a stream can erode called?
Base level
Which process involves the release of water into the atmosphere from plants through the ground?
Transpiration
What stream characteristic refers to the slope or steepness of a stream channel?
Gradient
In a stream, what does discharge refer to?
Volume of water flowing past a certain point in a unit of time
What is the movement of surface water into rock or soil through cracks and pore spaces called?
Infiltration
What type of valley often develops a course with many bends called meanders?
Broad, flat-bottomed valley near base level
Study Notes
Water Cycle
- Water constantly moves among the oceans, atmosphere, solid Earth, and biosphere in an unending circulation called the water cycle.
- Processes involved in the cycle are precipitation, evaporation, infiltration, runoff, and transpiration.
- Balance in the water cycle means the average annual precipitation over Earth equals the amount of water that evaporates.
Base Level
- Base level is the lowest point to which a stream can erode.
- There are two general types: ultimate (sea level) and temporary (local).
- A stream in a broad, flat-bottomed valley near its base level often develops a course with many bends called meanders.
Surface Water
- The ability of a stream to erode and transport materials depends largely on its velocity.
- Channel characteristics include:
- Gradient: the slope or steepness of a stream channel.
- Shape, size, and roughness.
- Discharge: the volume of water flowing past a certain point in a given unit of time.
- While gradient decreases between a stream's headwaters and mouth, discharge increases.
- Streams are termed differently on certain localities, such as Donga, Wadi, Wash, or Arroyo.
Depositional Landforms
- Alluvial Fans: formed when water comes out of the interior drainage, losing its competence, and sediments are deposited on the base of mountains.
- Bajada: when alluvial fans coalesce, forming an apron-like landform.
- Playa Lake: when alluvial fans form a basin-like landform, and the basin-floor becomes a shallow lake, which dries to become a Playa.
Erosional Landforms
- Desert Pavement: an exposed layer of coarse sediments (pebbles or larger), formed through deflation.
- Blowouts: shallow depressions formed through wind erosion.
- Tables: flat-topped mountains formed through wind erosion.
- Plateau: a mountain-sized landform formed through wind erosion.
- Mesa: a hill-sized, isolated part of a plateau formed through wind erosion.
- Butte: a hill-sized remnant of a plateau and/or a mesa formed through wind erosion.
- Yardang: a streamlined, wind-sculpted, exposed piece of bedrock.
Sand Storms
- Dune Migration: simultaneous erosion, transportation, and deposition of sand, which can sometimes mislead people that the sand dunes are alive.
- Dune migration depends on wind strength, with stronger winds causing faster migration and even stronger winds causing sandstorms.
Deserts
- Deserts are characterized by low moisture, where evaporation exceeds precipitation.
- Bodies of water come from outside the desert.
- Temperature is either too hot or too cold.
- Soil is high in mineral matter and low in organic matter.
- Weathering is reduced due to the lack of moisture, with principal weathering processes being:
- Mechanical weathering
- Water: creating channels through rocks or interior drainage
- Wind: picking up fine sediments and using them as an abrasive to solid rocks (sand blasting)
- Temperatures: hot days and cold nights in hot deserts, causing minerals to expand and contract unequally until it breaks down (thermal expansion)
- Ice: on cold deserts, when water is locked inside rocks, freezing and expanding, causing joints to enlarge, and then releasing when it melts (frost-wedging)
Running Water
- Running water, although infrequent, does the most erosional work.
- Ephemeral streams carry water in response to specific episodes of rainfall.
Test your knowledge on different landform depositional processes such as Alluvial Fans, Bajadas, and Playa Lakes. Learn about the formation of these landforms based on the role of water and deposition of sediments.
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