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When water freezes or when the temperature of soil drops to or below 0°C (32°F) it is known as frozen ground. Permafrost, or permanently frozen ground, is soil, sand, sediment, or rock that remains at or below 0°C (32°F) for at least two years. It occurs both on land and beneath offshore Arctic continental shelves.
- Science of Frozen Ground
When ground temperatures drop to 0°C (32°F), the water...
- Frozen Ground & Permafrost
What is frozen ground? When water turns into ice in soil, it...
- Science of Frozen Ground
When ground temperatures drop to 0°C (32°F), the water trapped in sediment, soil, and pores of rocks turns to ice. Once frozen, it is considered frozen ground. When ground remains frozen for at least two consecutive years, it is known as permafrost. Ground that freezes and thaws every year is called seasonally frozen ground.
- Overview
- Permafrost zones
- Study of permafrost
- Air temperature and ground temperature
permafrost, perennially frozen ground, a naturally occurring material with a temperature colder than 0 °C (32 °F) continuously for two or more years. Such a layer of frozen ground is designated exclusively on the basis of temperature. Part or all of its moisture may be unfrozen, depending on the chemical composition of the water or the depression of the freezing point by capillary forces. Permafrost with saline soil moisture, for example, may be colder than 0 °C for several years but contain no ice and thus not be firmly cemented. Most permafrost, however, is consolidated by ice.
Permafrost with no water, and thus no ice, is termed dry permafrost. The upper surface of permafrost is called the permafrost table. In permafrost areas the surface layer of ground that freezes in the winter (seasonally frozen ground) and thaws in summer is called the active layer. The thickness of the active layer depends mainly on the moisture content, varying from less than a foot in thickness in wet, organic sediments to several feet in well-drained gravels.
Permafrost is widespread in the northern part of the Northern Hemisphere, where it occurs in 85 percent of Alaska and 55 percent of Russia and Canada, and covers probably all of Antarctica. Permafrost is more widespread and extends to greater depths in the north than in the south. It is 1,500 metres (5,000 feet) thick in northern Siberia and 740 metres (about 2,430 feet) thick in northern Alaska, and it thins progressively toward the south.
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Most permafrost can be differentiated into two broad zones; the continuous and the discontinuous, referring to the lateral continuity of permafrost. In the continuous zone of the far north, permafrost is nearly everywhere present except under the lakes and rivers that do not freeze to the bottom. The discontinuous zone includes numerous permafrost-free areas that increase progressively in size and number from north to south. Near the southern boundary, only rare patches of permafrost have been found to exist.
In addition to its widespread occurrence in the Arctic and subarctic areas of Earth, permafrost also exists at lower latitudes in areas of high elevation. This type of perennially frozen ground is called alpine permafrost. Although data from high plateaus and mountains are scarce, measurements taken below the active surface layer indicate zones where temperatures of 0 °C or colder persist for two or more years. The largest area of alpine permafrost is in western China, where 1,500,000 square km (580,000 square miles) of permafrost are known to exist. In the contiguous United States, alpine permafrost is limited to about 100,000 square km (about 38,600 square miles) in the high mountains of the west. Permafrost occurs at elevations as low as 2,500 metres (8,200 feet) in the northern states and at about 3,500 metres (about 11,500 feet) in Arizona.
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Although the existence of permafrost had been known to the inhabitants of Siberia for centuries, scientists of the Western world did not take seriously the isolated reports of a great thickness of frozen ground existing under northern forest and grasslands until 1836. Then, Alexander Theodor von Middendorff measured temperatures to depths of approximately 100 metres (328 feet) of permafrost in the Shargin shaft, an unsuccessful well dug for the governor of the Russian-Alaskan Trading Company, at Yakutsk, and estimated that the permafrost was 215 metres (705 feet) thick. Since the late 19th century, Russian scientists and engineers have actively studied permafrost and applied the results of their learning to the development of Russia’s north.
In a similar way, prospectors and explorers were aware of permafrost in the northern regions of North America for many years, but it was not until after World War II that systematic studies of perennially frozen ground were undertaken by scientists and engineers in the United States and Canada. Since exploitation of the great petroleum resources on the northern continental shelves began in earnest in the 1970s, investigations into subsea permafrost have progressed even more rapidly than have studies of permafrost on land.
In areas where the mean annual air temperature becomes colder than 0 °C (32 °F), some of the ground frozen in the winter will not be completely thawed in the summer, and, therefore, a layer of permafrost will form and continue to grow downward gradually each year from the seasonally frozen ground. The permafrost layer will become thicker each winter, its thickness controlled by the thermal balance between the heat flow from Earth’s interior and that flowing outward into the atmosphere. This balance depends on the mean annual air temperature and the geothermal gradient. The average geothermal gradient is an increase of 1 °C (1.8 °F) for every 30 to 60 metres (roughly 100 to 200 feet) of depth. Eventually the thickening permafrost layer reaches an equilibrium depth at which the amount of geothermal heat reaching the permafrost is on the average equal to that lost to the atmosphere. Thousands of years are required to attain a state of equilibrium where permafrost is hundreds of feet thick.
The annual fluctuation of air temperature from winter to summer is reflected in a subdued manner in the upper few metres of the ground. This fluctuation diminishes rapidly with depth, being only a few degrees at 7.5 metres (about 25 feet), and is barely detectable at 15 metres (49 feet). The level of zero amplitude, at which fluctuations are hardly detectable, is 9 to 15 metres (30 to 49 feet). If the permafrost is in thermal equilibrium, the temperature at the level of zero amplitude is generally regarded as the minimum temperature of the permafrost. Below this depth the temperature increases steadily under the influence of heat from Earth’s interior. The temperature of permafrost at the depth of minimum annual seasonal change varies from near 0 °C at the southern limit of permafrost to −10 °C (14 °F) in northern Alaska and −13 °C (9 °F) in northeastern Siberia.
What is frozen ground? When water turns into ice in soil, it becomes frozen ground. This frozen soil has a temperature at or below 0 °C (32 °F). More than half of all the land in the Northern Hemisphere freezes and thaws every year. Seasonally frozen ground is near-surface soil that freezes for more than 15 days per year.
Frozen ground occurs when ground water freezes due to the temperature of the ground being below 0 °C. [1] The ground freezes when the water freezes between rocks, soil, and pebbles. In this context, this frozen water is called pore ice. [2] The ground freezes when the water in the ground becomes ice and the ground thaws when the pore ice melts.
Oct 5, 2023 · Frozen Ground. Soil within which the moisture has predominantly changed to ice, the unfrozen portion being in vapor phase. Ice within the soil bonds (adfreezes) adjacent soil particles and renders frozen ground very hard. Permanently frozen ground is called permafrost. Dry frozen ground is relatively loose and crumbly because of the lack of ...
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Sep 25, 2024 · Permafrost is any ground that remains completely frozen—32°F (0°C) or colder—for at least two years straight. These permanently frozen grounds are most common in regions with high mountains and in Earth’s higher latitudes—near the . Permafrost covers large regions of the Earth.
