NPS Photo/Dale Pate
Introduction
Arid regions by definition receive little precipitation—less than 10 inches (25 centimeters) of rain per year. Semi-arid regions receive 10 to 20 inches (25 to 50 centimeters) of rain per year. Although the rocks and tectonic features underlying arid regions may not differ from other areas, the landscape is distinctive. With little vegetation and often loose surface material, erosion is the main factor in shaping the land surface.
Trista L. Thornberry-Ehrlich, Colorado State University.
Erosional processes in arid and semi-arid regions include:
-
mass wasting (surface creep, landslides, mud and debris flows, and rock topples and falls),
-
water-driven or fluvial processes, and
-
wind-driven or aeolian processes (dust, loess, sand dunes).
Surprisingly, water is an important agent of erosion in arid lands. Although streams may only be active during and right after a heavy rain, running water during a flash flood can carry tremendous amounts of material.
Erosional Features and Landforms
Mesas and Buttes
Mesas are broad flat topped mountains with at least one steep side. Buttes are smaller flat topped mountains or hills with steep slopes on all sides.
Spires (also towers, needles, and balanced rock) are slender isolated columns of rock, that form as the erosional remnant of a butte.
Canyons form as narrow, steep-walled gorges carved by a swift-moving water.
Arroyos or washes are dry stream beds that fill temporarily during rain storms. Flash floods are common following thunderstorms.
Pediments are gently sloping near-bedrock surfaces at the base of a receding mountain front, formed when erosion removes much of the mountain’s mass.
An Inselberg is an isolated, steep-sided knob or hill that risines abruptly from a lowland pediment. An inselberg is an erosional remnant of resistant rock that has remained as surrounding areas eroded away.
Desert pavement is a closely-packed surface layer of coarse pebbles and gravel.
Badllands
Natural Arches
Depositional Features and Landforms
Alluvial fans are fan-shaped piles of sediment that form where a rapidly flowing mountain stream enters a relatively flat valley. As water slows down, it deposits sediment (alluvium). As the stream migrates back and forth in the open valley, the sediment gradually builds a fan.
Bajadas are are aprons of rocky debris that form when alluvial fans coalesce to form a ramp that spreads out toward the valley floor. A bajada or piedmont slope partially buryies the range front in its own sediment.
Stream terraces are long bench-like surface bordering a stream or wash. A terrace is a level or near-level area of land above a water course and separated from it by a steeper slope. A stream terrace is made by the stream at some time in the past when the river flowed at a higher level. A terrace may be made of stream deposits such as gravel or sand, or it could be an erosional cut by the stream on bedrock.
Playas are shallow, short-lived lakes that form where water drains into basins with no outlet to the sea and quickly evaporates. Playas are common features in arid (desert) regions and are among the flattest landforms in the world.
Basins are depression in the Earth’s surface that collect sediment. Rock particles that wash down from mountain sides collect in adjacent basins, in some places burying the bedrock under thousands of feet of rock debris.
Showing results 1-3 of 3
- Geologic Resources Division
Monitoring River Systems and Fluvial Landforms
- Offices: Geologic Resources Division
Stream channels and fluvial landforms are influenced by the complex interplay among regional geology, climate, topographic gradient, river history, drainage basin hydrology, and sediment load. The geologic monitoring manual provides guidance for resource managers seeking to establish the status and trends of geologic resources within the National Park System, and to further the understanding of how geologic processes impact dynamic ecosystems.
- Geologic Resources Division
Monitoring Slope Movements
- Offices: Geologic Resources Division
Different types of slope movement, such as fall, topple, slide, spread, and flow, can occur in a variety of materials and degrees of slopes. The geologic monitoring manual provides guidance for resource managers seeking to establish the status and trends of geologic resources within the National Park System, and to further the understanding of how geologic processes impact dynamic ecosystems.
- Geologic Resources Division
Monitoring Aeolian Features and Processes
- Offices: Geologic Resources Division
Aeolian processes, involving erosion, transportation, and deposition of sediment by the wind, occur in a variety of environments, including the coastal zone, cold and hot deserts, and agricultural fields. The geologic monitoring manual provides guidance for resource managers seeking to establish the status and trends of geologic resources within the National Park System, and to further the understanding of how geologic processes impact dynamic ecosystems.
Photo Gallery
Arid and Semi-Arid Region Land...
11 Images
A collection of arid and semi-arid landform examples in parks.
Showing results 1-8 of 8
- Locations: Arches National Park, Canyon de Chelly National Monument, Canyonlands National Park, Capitol Reef National Park, Colorado National Monument, more »
- Offices: Geologic Resources Division
Ever wondered what those dark lines were on the rock walls of canyon country? These black, brown, and red streaks are called desert varnish.
- Locations: Arches National Park, Canyonlands National Park, Capitol Reef National Park, Colorado National Monument
A bouquet of tiny arches? A miniature cave system? Known as honeycomb weathering or "swiss-cheese rock," tafoni (singular: tafone) are small, rounded, smooth-edged openings in a rock surface, most often found in arid or semi-arid deserts.
- Locations: Arches National Park, Canyonlands National Park, Capitol Reef National Park, Hovenweep National Monument, Natural Bridges National Monument
Those bright colors you may see on sandstone and biological soil crust are alive! Lichens grow in every size, shape, and color in Southeast Utah.
- Locations: Arches National Park, Canyonlands National Park, Capitol Reef National Park, Hovenweep National Monument, Natural Bridges National Monument
Be careful where you step because the dirt is alive! This bumpy, lumpy, crust black soil is called biological soil crust and is made up of living organisms.
- Canyonlands National Park
Needles
- Locations: Canyonlands National Park
In the southeast corner of Canyonlands, spires of Cedar Mesa Sandstone rise hundreds of feet above a network of canyons and grasslands know as "The Needles."
- White Sands National Park
Linking Dune Formation with Atmospheric Processes at White Sands NM
- Locations: White Sands National Park
Desert sand dunes interact strongly with external drivers, including wind, vegetation, and groundwater. Given the ubiquity of sand dunes on Earth’s deserts and on extraterrestrial environments, this research attempts to understand how dune fields respond to these complex external forces.
- Locations: Arches National Park, Canyonlands National Park, Hovenweep National Monument, Natural Bridges National Monument
Ephemeral pools are a vital source of water in a parched desert.
- Arches National Park
Types of Arches
- Locations: Arches National Park
Every arch in the park is as unique as a fingerprint, telling its own personal story of rock, water, time and change. When discussing them scientifically, however, it's helpful to group them into categories by their shape or apparent mechanism of formation.
Last updated: September 13, 2019