In the study of Geography, understanding the physical processes and landscapes in extreme environments is crucial. These environments, such as glacial and hot arid regions, exhibit unique physical processes and landforms shaped by various natural forces. This study note will delve into the key aspects of these extreme environments, covering glacial processes and landforms, periglacial processes and landforms, as well as the processes and landforms found in hot arid environments.
Glaciers play a significant role in shaping landscapes through weathering, erosion, transportation, and deposition. Key processes include:
- Freeze-thaw weathering:
- Occurs when water enters cracks in rocks and freezes.
- The expansion of ice exerts pressure on the rock, causing it to break apart over repeated cycles of freezing and thawing.
Example
Imagine a rock with a small crack. During the day, water seeps into the crack. At night, temperatures drop below freezing, causing the water to freeze and expand. Over time, this process enlarges the crack and eventually breaks the rock apart.
- Glaciers transport eroded material through processes like plucking and abrasion.
- When glaciers melt, they deposit this material, forming various landforms such as moraines and drumlins.
As glaciers move, they erode the underlying rock, creating distinct features:
- Pyramidal Peak: A sharply pointed mountain peak formed by the erosion of multiple glaciers converging from different directions.
- Arête: A narrow ridge formed between two glacial valleys or cirques.
- Corrie/Cwm/Cirque: A bowl-shaped depression on a mountainside, carved by a glacier.
- Tarn: A small lake formed in a cirque.
- Truncated Spur: A ridge that has been cut off by a glacier.
- Hanging Valley: A valley that is cut across by a deeper valley or a cliff.
- Ribbon Lake: A long, narrow lake formed in a glacial trough.
- Glacial Trough/U-shaped Valley: A valley with a U-shaped cross-section, formed by glacial erosion.
Tip
When studying glacial landforms, it is helpful to visualize the processes by looking at diagrams and photographs of real-world examples.
Periglacial landscapes are characterized by permafrost and a seasonally active layer. Key processes include:
- Freeze-thaw weathering (frost shattering):
- Similar to glacial environments, this process breaks rocks into angular fragments.
- These fragments accumulate at the base of slopes, forming scree.
- Solifluction:
- A slow, downslope flow of water-saturated soil.
- Can occur in two forms: fast solifluction (rapid movement) and slow solifluction (gradual movement).
- Blockfields (Felsenmeer): Vast plains of angular, broken rocks formed by intense freeze-thaw action.
- Patterned Ground: Surface features such as circles, polygons, and stripes formed by the freeze-thaw cycle in permafrost regions.
Note
Periglacial regions are dominated by permafrost, which is ground that remains below 0°C for at least two consecutive years.
Weathering in hot arid environments is primarily physical due to extreme temperature variations:
- Thermal Fracture:
- Rocks expand during the day due to intense heat and contract at night as temperatures drop.
- This repeated expansion and contraction cause rocks to fracture and break apart.
- Wind Erosion:
- Wind can erode and shape rocks, creating features such as deflation hollows and desert pavements.
- Ventifacts: Faceted pebbles shaped by wind-blown sediment.
- Yardangs: Streamlined ridges formed by wind erosion.
- Rock Pedestals: Mushroom-shaped rocks formed by wind erosion at the base.
- Water Action:
- Although rare, flash floods can carve out canyons and wash away loose material.
Distinct landforms created by wind action include:
- Deflation Hollows: Depressions formed by the removal of loose particles by wind.
- Desert Pavements: Surfaces covered with closely packed, interlocking rock fragments.
- Ventifacts: Rocks shaped by wind-blown sand.
- Yardangs and Zeugens: Elongated ridges formed by wind erosion.
- Rock Pedestals: Rocks with a narrow base and wider top, formed by differential wind erosion.
Common Mistake
A common misconception is that deserts are devoid of life. In reality, many deserts support a variety of plant and animal species adapted to extreme conditions.
In hot arid environments (such as deserts), the water cycle operates differently from more temperate or humid regions due to high temperatures, low precipitation, and high rates of evaporation. These areas receive less than 250mm of rainfall annually, and the processes of the water cycle are often limited by the lack of available water.
Key Processes in the Water Cycle of Arid Regions:
- Evaporation:
- High temperatures in arid environments lead to intense evaporation, where water is rapidly lost from any available surface water sources (e.g., rivers, lakes) or soil.
- Precipitation:
- Rainfall is rare and irregular. When it does occur, it is often in the form of short, intense storms that can cause flash floods due to the inability of the dry, compacted soil to absorb water quickly.
- Runoff:
- When rain does fall, surface runoff is high because arid soils are often hard and compact, reducing infiltration. Water flows quickly over the surface, often collecting in temporary streams or valleys called wadis.
- Infiltration and Groundwater Recharge:
- In some areas, limited infiltration of water into the ground occurs, recharging underground aquifers that can sustain oases. However, infiltration is often minimal due to the impermeable nature of desert soils.
- Transpiration:
- Transpiration from plants is limited because arid environments typically have sparse vegetation. Plants that do survive in deserts are adapted to reduce water loss.
- Condensation and Dew:
- At night, temperatures drop significantly, causing water vapor in the air to condense into dew, which can be a small but vital source of moisture for plants and animals.
Wadis:
A wadi is a dry riverbed or valley that temporarily fills with water during heavy rainstorms. In arid environments, rain events are rare but often intense, leading to rapid surface runoff that carves out channels in the landscape. These channels remain dry for most of the year, only carrying water during and immediately after rainfall.
Formation:
- Flash Flooding: When rain falls, particularly in mountainous desert regions, water quickly flows down the slopes, creating torrents of water that carve out channels in the desert floor. These temporary rivers can lead to significant erosion, deepening and widening the wadi over time.
- Ephemeral Nature: Wadis are typically ephemeral; they only carry water during specific, short-lived rain events. Most of the year, they are dry, but after a rainstorm, they can become fast-flowing streams for a brief period.
Tip
Wadis are common in the Middle East and North Africa, such as Wadi Rum in Jordan.
Oases:
An oasis is a fertile area in a desert where water is available, typically from an underground source such as a spring or aquifer. Oases allow for the growth of vegetation and are crucial for supporting human habitation and agriculture in otherwise inhospitable environments.
Formation:
- Groundwater Sources: Oases form in places where groundwater, stored in underground aquifers, reaches the surface. This can happen through natural springs or where humans dig wells to access underground water.
- Runoff Collection: In some cases, oases form in low-lying areas where runoff from rare rainfall events collects and recharges groundwater, maintaining the water supply over time.
Significance:
- Oases are vital to life in arid environments, providing water for agriculture, drinking, and supporting settlements. They have historically been hubs of trade routes, such as those in the Sahara Desert, where caravans would stop to replenish water supplies.
Example
The Siwa Oasis in Egypt is a well-known example, where water from underground aquifers sustains date palms and olive groves, supporting local communities.
Understanding the physical processes and landscapes in extreme environments is essential in Geography. Glacial and periglacial processes shape cold environments through mechanisms like freeze-thaw weathering and glacial erosion, creating unique landforms. In hot arid environments, physical weathering and wind action dominate, leading to distinct desert landscapes. By studying these processes and landforms, we gain insights into the dynamic nature of Earth's surface.