Category Geography

Deserts are dry for different reasons depending on where they are. Winds in sub-tropical deserts, such as the Sahara in northern Africa, prevent rain clouds from forming. Coastal deserts, like the Atacama in Chile, get no rain, just a little moisture from fog. Death Valley, in California, USA, is a rain shadow desert on mountainsides that face away from rain-filled winds. The Gobi, in Mongolia, is an interior desert; rain-bearing winds cannot reach so far inland. Polar deserts, such as the Arctic and Antarctic, are dry because the water is locked as ice.

Areas that receive less than 25 centimeters (10 inches) of rain annually are called deserts. Deserts are dry with sparse vegetation. Landforms tend to have angular features because the lack of rain results in minimal chemical weathering, and flash floods create steep?walled scarps and gullies. There are few plants to protect the soil from the wind, so the soil is blown away to expose the rocky surface. Even in such a dry climate, most of the landforms are carved by the rare periods of heavy rainfall that result in flash floods, erosion, and sediment deposition.

Hot air rises at the equator, where the land receives the greatest amount of the sun’s radiation. Most of the world’s deserts are located near 30 degrees north latitude and 30 degrees south latitude, where the heated equatorial air begins to descend. The descending air is dense and begins to warm again, evaporating large amounts of water from the land surface. The resulting climate is very dry.

Other deserts are located in the rain shadows of mountain ranges. As moist air passes over a mountain range, it expands and cools, precipitating most of its moisture as it rises. As it sweeps down the other side of the mountain range, it warms and compresses, causing high evaporation rates and shedding little rain. Many of the deserts in the southwestern United States are the result of rain shadows.

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Deserts can have extremes in temperature. Daytime may get as hot as 54°C in hot deserts, while at night, dryness and lack of cloud cover cause a sharp drop in temperature, and it can get as cold as 4°C.

As extremes of nature go, the marked contrast in temperature of a desert during the day and at night is one of the most impressive. Searing heat can torture human occupants. After dark, the problem is reversed, and a winter jacket might prove useful. On average, temperatures in Africa’s Sahara Desert can swing an astounding 75 degrees in 24 hours, rising to an average 100°F with the sun out and plummeting to 25°F after it sets.

When the sun is out, sand proves to be an effective distributor of heat, reflecting it back into the air. But it’s not very good at retaining heat. Once the sun goes down, heat from the sand is released quickly.

The thing that could help retain warm air overnight is humidity, but deserts don’t have much of that. Water vapor in the air traps heat: Think of it like an insulating blanket, preventing either heat or cold from dispersing into the air. When the heat source is taken away, that vapor will retain it for long periods. Without sun or humidity, daytime heat isn’t being held anywhere, and the desert will cool rapidly.

Humidity is also why deserts can feel hotter than other places even though the temperature is the same. The water vapor needs lots of solar energy to heat up, while a dry climate takes that energy head-on.

All of this happens quickly because of that lack of humidity. Just as warm air escapes when night falls, there’s no humidity to trap the chilly evening weather. When the sun rises, it’s back to scorching.

Other factors can come into play. Clouds that help moderate temperature and wind can both help keep temperatures from dropping. But generally, you’ll roast in a desert and then freeze because the combination of sand and low humidity isn’t really suited for comfortable and consistent climates.

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Ice eggs are a rare phenomenon in which small pieces of ice are rolled over by wind and water. Chunks of ice break off from larger ice sheets in the sea and wash up on shore on the incoming tide or are pushed in by gusts of wind at the water’s surface. Waves strike the ice chunks as they travel, slowly eroding their jagged edges into smooth curves. Seawater sticks and freezes to the forming eggs, causing them to grow. Once the ice chunks reach the shore, the pounding waves smooth out any lingering sharp edges on their surfaces, leaving behind shiny “eggs”.

Given enough time, the frozen balls can grow to become boulder size. In 2016, giant snowballs washed up on a beach in Siberia, some measuring a metre (about 3 feet) across. An ice specialist from the Finnish Meteorological Institute has been quoted as saying ice balls are rare but not unprecedented, and occur about once a year on the Finnish coastline as conditions allow. They also appear on the American Great Lakes where they are called Ice balls.

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Deserts are vast and extremely dry lands, which receive very little or no rainfall. They can be both hot and cold – in both cases, the amount of evaporation is higher than the precipitation received, and the land remains very dry.

A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one third of the land surface of the world is arid or semi-arid. This includes much of the Polar Regions where little precipitation occurs and which are sometimes called “cold deserts”. Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.

Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor is further eroded by the wind. This picks up particles of sand and dust and wafts them aloft in sand or dust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down, and the wind sorts sand into uniform deposits. The grains end up as level sheets of sand or are piled high in billowing sand dunes. Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones. These areas are known as desert pavements and little further erosion takes place. Other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water in the form of springs and seepages from aquifers. Where these are found, oases can occur.

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The sheer weight and size of glaciers give them an enormous power to carve out the landscape. Much like mega bulldozers, they crush and grind everything that comes in their way, pushing the debris along until it is deposited in distinctive piles called moraine.

Glaciers are huge masses of ice that move across the land. ?Glaciers? are often called rivers of ice for the way they move down mountainsides and carve valleys. Though climate change is threatening glaciers today, there are still many glaciers changing landscapes around the world through erosion and material deposition. Glacial landforms left behind by glaciers include moraines, drumlins, troughs, aretes, horns and cirques.

There are three distinct ways that glaciers shape the land: 1) erosion 2) transportation and 3) deposition. Erosion picks up material through weathering through plucking and abrasion. That material is then transported as it moves downhill. Sometimes the material is hidden inside or at the base of the glacier, or sometimes it is on top of the glacier, accounting for the dirty color of some glaciers. Those rocks and other transported materials eventually get deposited to a new place as the glacier melts; this leftover material is called glacial till, and it’s what forms many of our landscapes today from the last ice age!

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When they form in the high mountains, these rivers of ice are called alpine glaciers. They flow down through the mountains, cutting and breaking up the rocks, creating sharp peaks, ridges and gouging out unique, U-shaped valleys.

A glacier that is surrounded by mountains is called an alpine or mountain glacier. They are a persistent body of snow that moves under its weight at a slow pace. Alpine glaciers are a sheet of snow that forms over a cirque or high rock basin. The iceberg’s uppermost layer is brittle, but the ice beneath behaves like a plastic substance flowing gently.

The glacier usually forms in a cirque or high rock basin where snow accumulates throughout the year. The most amazing fact about this glacier is that the rate of accumulation at the upper surface balances the rate of evaporation and melting at the lower end.

The glacier begins to occupy a sloping valley situated in between the creeks or steep rock walls. Following that, the accumulation of snow occurs at the upper part of the bowl-shaped depression called a cirque.

The glacial ice starts flowing downwards, slowly abrading and plucking the bedrock. The accumulation of snow that is compacting and recrystallizing is called firn.

The flow then accelerates across the steep rock where the deep crevasses or gaping fractures mark the icefall. The lower part of the glacier denotes ablation. As the ice thins, it evaporates and melts, thereby losing its plasticity. There are chances of developing fissures, as the glacier tries depositing debris at the terminus when it melts.

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