Landforms: Formation and Types – From Pyramids to Glaciers
Fairy Chimneys: Pyramidal Landforms
Fairy chimneys are huge pyramids topped with rocks. These landforms are created when water carries away the finest materials, leaving behind areas protected by water-resistant rocks.
Wadis: Ephemeral Water Channels
Wadis are found in dry and sub-arid regions where it rains infrequently. When it does rain, it is often torrential, digging channels. These channels, called wadis, only carry water after a strong storm. They are wide, shallow, and can carry enormous amounts of material in a short time. In some Mediterranean regions, water forms channels similar to a wadi, called ramblas or rieras. Wadis are almost always dry and only carry water during heavy rains or the wet season of the year.
Permanent Waters: Rivers
Rivers receive water from rain, melting snow and ice, and groundwater, transporting it to the sea. The river water and the materials it carries excavate a channel through which the river flows.
River Erosion at its Headwaters
At its source, a river runs through mountainous areas. The force of the water and the materials it carries dig a narrow, V-shaped valley. If the rocks through which the channel passes are hard, it can form gorges. When there are steep slopes in the channel, it creates rapids, waterfalls, or cataracts, depending on their size.
The River in its Middle Course
In the middle and lower courses, the slope is lower, and the river flows through a wide valley. The river water flows over sediments that it deposits. These sediments form an alluvial plain or meadow, often used as fertile cultivation areas.
The River Mouth
At the mouth, the valley is very wide, and the channel is wide and shallow. If rivers flow into open seas, they form estuaries. If they flow into shallow coastal areas, they form deltas.
A delta is constituted by sediment that the river deposits as it flows into the sea through opening channels.
Glaciers: Rivers of Ice
Glaciers are formed when accumulated snow in mountaintops moves due to gravity, forming rivers of ice called alpine glaciers.
Glacial Valleys and Cirques
The area where snow accumulates and turns into ice is called a glacial cirque, shaped like a basin around a mountain. When various cirques form, they create a pyramidal peak called a horn. The cirque gives way to the glacial tongue, where the ice descends slowly down the mountain.
Glacial Erosion and Moraines
The glacier erodes the soil and digs a U-shaped valley. When the glacier tongue reaches a level where the average temperature is higher, the ice melts, and the transported materials are deposited, forming moraines.
Wind Erosion: Shaping Arid Landscapes
Wind is a significant agent in shaping the relief of arid, sub-arid, and semi-desert regions of the Earth.
Deflation and Oasis Formation
When the wind sweeps away loose materials, it produces an effect called deflation. If it reaches a layer containing water, it can result in oases or springs. The sand grains carried by the wind continuously wear down the rocks they impact, an effect called corrasion.
Stone Deserts
Stone deserts are characterized by surfaces completely covered with pebbles. They form because the wind sweeps away the finest materials, leaving behind the heavier pebbles that cover the entire surface.
Dunes: Shifting Sands
Wind moves loose material and deposits it where its force ceases, forming ripples called dunes. In deserts with plenty of sand, dunes cover the surface and are separated by ridges called transverse dunes. These dunes are the most typical.