From this article you will learn about the features of permafrost soils, which are common in permafrost zones. In geology, permafrost is land, including stone (cryotic) soil, relevant at a freezing temperature of 0 ° C or lower for two or more years. Most of the permafrost is located in high latitudes (in and around the Arctic and Antarctic regions), but, for example, is found in the Alps and higher.
Ground ice is not always present, as may be the case with non-porous bedrock, but it is often found in amounts exceeding the potential hydraulic saturation of the ground material. Permafrost makes up 0.022% of the total water on Earth and exists in 24% of the open lands of the Northern Hemisphere. It also occurs underwater on the continental shelves of the continents surrounding the Arctic Ocean. According to one group of scientists, a global temperature increase of 1.5 ° C (2.7 ° F) above current levels will be enough to start thawing permafrost in Siberia.
The study
In contrast to the relative lack of reports on frozen soils in North America before World War II, literature on the engineering aspects of permafrost was available in Russian. Beginning in 1942, Simon William Muller delved into relevant literature from the Library of Congress and the U.S. Geological Survey Library to provide the government with engineering guidance and a technical report on permafrost by 1943.
Definition
Permafrost soils are soils, rocks or sediments that freeze for more than two consecutive years. In areas not covered by ice, they exist under a layer of soil, stone or sediment, which freezes and thaws every year and is called the “active layer”. In practice, this means that permafrost occurs at an average annual temperature of -2 ° C (28.4 ° F) or lower. The thickness of the active layer varies depending on the season, but ranges from 0.3 to 4 meters (shallow along the Arctic coast; deep in southern Siberia and on the Qinghai-Tibet Plateau).
Geography
What can be said about the distribution of permafrost soils? The degree of permafrost varies depending on the climate: today in the Northern Hemisphere 24% of the land area free from ice - which is equivalent to 19 million square kilometers - is more or less affected by permafrost.
In this area, just over half is covered by continuous permafrost, about 20 percent - by intermittent permafrost, and slightly less than 30 percent - by sporadic permafrost. Most of this territory is located in Siberia, northern Canada, Alaska and Greenland. Under the active layer, annual fluctuations in permafrost temperature become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains temperatures above zero. Above this limit there may be permafrost, the temperature of which does not change annually. This is "isothermal permafrost." Areas of permafrost soils are poorly suited for active human life.
Climate
Permafrost is usually formed in any climate where the average annual air temperature is less than the freezing point of water. Exceptions can be found in humid winters, for example, in northern Scandinavia and northeastern Russia west of the Urals, where snow acts as an insulating coating. Glacial sites may be exceptions. Since all glaciers are heated at the base with geothermal heat, temperate glaciers that are near the melting point under pressure may have liquid water on the border with the ground. Therefore, they are free from permafrost. “Fossil” cold anomalies in a geothermal gradient in areas where deep permafrost developed during the Pleistocene are preserved up to several hundred meters. This is evident from temperature measurements in wells in North America and Europe.
Temperature underground
Typically, the temperature below the ground varies from season to season less than air temperature. At the same time, average annual temperatures tend to increase with depth as a result of the geothermal gradient of the earth's crust. Thus, if the average annual air temperature is only slightly below 0 ° C (32 ° F), permafrost will only form in places that are protected - usually from the north side - creating intermittent permafrost. Typically, permafrost will remain intermittent in a climate where the average annual soil surface temperature is –5 to 0 ° C (23 to 32 ° F). In the wet winter areas mentioned above, there may not even be intermittent permafrost up to -2 ° C (28 ° F).
Types of permafrost
Permafrost is often further divided into vast intermittent permafrost, where permafrost covers 50 to 90 percent of the landscape and is commonly found in areas with an average annual temperature of -2 to -4 ° C (28-25 ° F), as well as sporadic permafrost where permafrost cover is less than 50 percent of the landscape and usually occurs at an average annual temperature of 0 to -2 ° C (32 and 28 ° F). In soil science, the sporadic permafrost zone is SPZ, and the vast intermittent permafrost zone is DZZ. Exceptions occur in unglazed Siberia and Alaska, where the current depth of permafrost is a relic of climatic conditions during the ice age, where winters were 11 ° C (20 ° F) colder than today.
Permafrost soil temperature
At average annual soil surface temperatures below -5 ° C (23 ° F), the influence of the aspect can never be sufficient to thaw permafrost and form a zone of continuous permafrost (abbreviated as CPZ). The line of continuous permafrost in the Northern Hemisphere is the southernmost border, where the land is covered by continuous permafrost or glacial ice.
For obvious reasons, designing on permafrost is extremely difficult. The line of permafrost is changing all over the world to the north or south due to regional climatic changes. In the southern hemisphere, most of the equivalent line would be in the Southern Ocean if there were land. Most of the Antarctic continent is covered by glaciers, under which most of the area is prone to melting in the ground. The exposed land of Antarctica largely lies in permafrost.
Alps
Estimates of the total area of the permafrost zone in the Alps vary greatly. Bokheim and Munro combined the three sources and made tabular estimates by region (a total of 3,560,000 km2).
The Alpine permafrost in the Andes was not on the map. The length in this case is modeled to estimate the amount of water in these areas. In 2009, a researcher from Alaska discovered permafrost at 4,700 m (15,400 ft) at the highest peak in Africa, Mount Kilimanjaro, about 3 ° north of the equator. Foundations on permafrost soils in these latitudes are not uncommon.
Frozen seas and frozen bottom
Permafrost is found under the seabed and exists on the continental shelves of the polar regions. These areas formed during the last ice age, when most of the Earth’s water was connected in land ice sheets and sea levels were low. When the ice sheets melted and again became sea water, permafrost turned into flooded shelves under relatively warm and salty boundary conditions compared to permafrost on the surface. Therefore, underwater permafrost exists in conditions that lead to its reduction. According to Osterkamp, underwater permafrost is a factor in the “design, construction and operation of coastal facilities, seabed facilities, artificial islands, subsea pipelines and wells drilled for exploration and production.
Permafrost extends to the depth of the base, where geothermal heat from the Earth and the average annual surface temperature reach an equilibrium temperature of 0 ° C. The depth of the permafrost reaches 1493 meters (4898 feet) in the northern basins of the Lena and Yana rivers in Siberia. A geothermal gradient is the rate of increase in temperature relative to an increase in depth in the bowels of the earth. Far from the boundaries of the tectonic plate, it is about 25-30 ° C / km near the surface in most countries of the world. It varies depending on the thermal conductivity of the geological material and less for permafrost in soil than in bedrock.
Ice in the soil
When the ice content in permafrost exceeds 250 percent (from the mass of ice to dry soil), it is classified as massive ice. Massive ice bodies can vary in composition from icy mud to pure ice. Massive ice layers have a minimum thickness of at least 2 meters, a short diameter of at least 10 meters. The observations first recorded in North America were made by European scientists on the Canning River in Alaska in 1919. Russian literature cites an earlier date of 1735 and 1739 during the Great Northern Expedition of P. Lassinia and H.P. Laptev, respectively. Two categories of massive ground ice are buried surface ice and the so-called “intra-seat ice”. The creation of any foundation on permafrost soils requires that no large glaciers be nearby.
Buried surface ice can come from snow, frozen lake or sea ice, aufeis (twisted river ice) and probably the most common variant is buried glacier ice.
Groundwater freezing
Intradiastimal ice is formed as a result of freezing groundwater. Here, segregation ice predominates, which arises as a result of crystallization differentiation that occurs during wet sediment freezing. The process is accompanied by the migration of water to the freezing front.
Intradiastimal (constitutional) ice has been widely observed and studied throughout Canada, and also includes intrusive and injection ice. In addition, ice wedges, a separate type of ground ice, produce recognizable patterned polygons or tundra polygons. Ice wedges form in a pre-existing geological substrate. They were first described in 1919.
Carbon cycle
The permafrost carbon cycle is associated with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to the atmosphere, back to vegetation and, finally, again to permafrost soil by burial and sedimentation as a result of cryogenic processes. Part of this carbon is transported to the ocean and other parts of the globe through the global carbon cycle. The cycle includes the exchange of carbon dioxide and methane between terrestrial components and the atmosphere, as well as the transfer of carbon between land and water in the form of methane, dissolved organic carbon, dissolved inorganic carbon, inorganic carbon particles and organic carbon particles.
History
The permafrost of the Arctic has been declining for many centuries. The result is thawing of the soil, which may be weaker, and methane emissions, which contributes to an increase in the rate of global warming as part of the feedback cycle. The areas of permafrost distribution in history have been constantly changing.
At the last glacial maximum, continuous permafrost covered a much larger area than today. In North America, just south of the ice sheet in New Jersey latitude in southern Iowa and northern Missouri, there was only a very narrow permafrost belt. It was extensive in the drier western regions, where it extended to the southern border of Idaho and Oregon. In the southern hemisphere, there is some evidence of the former permafrost of this period in central Otago and in the Argentine Patagonia, but it was probably intermittent and related to the tundra. Alpine permafrost also occurred in Drakensberg during the existence of glaciers above 3,000 meters (9,840 feet). Nevertheless, foundations and foundations on permafrost soils are established even there.
Soil structure
Soil may consist of many substrate materials, including bedrock, sediment, organic matter, water or ice. Frozen land is that which is below the freezing point of water, regardless of whether water is present in the substrate. Ground ice is not always present, as may be the case with non-porous bedrock, but it is often found and may be present in amounts exceeding the potential hydraulic saturation of the thawed substrate.
As a result, rainfall increases, which in turn leads to weakening and possible collapse of buildings in areas such as Norilsk in northern Russia, which lies in the permafrost zone.
Slope destruction
Over the past century, many cases of destruction of alpine slopes in mountain ranges around the world have been recorded. It is expected that a large number of structural damage is associated with the melting of permafrost, which is believed to occur due to climate change. It is believed that permafrost thaw contributed to the Val Paul landslide in 1987, which killed 22 people in the Italian Alps. In mountain ranges, most of the structural stability can be associated with glaciers and permafrost. As the climate warms up, permafrost thaws, which leads to a less stable mountain structure and, ultimately, to a greater number of slope destruction. An increase in temperature allows deeper depths of the active layer, which entails even greater penetration of water. Ice in the soil melts, causing loss of soil strength, accelerated movement, and potential streams of debris. Therefore, construction on permafrost soils is extremely undesirable.
Information is also known about massive falls of rocks and ice (up to 11.8 million m 3 ), earthquakes (up to 3.9 million m 3 ), floods (up to 7.8 million m 3 water) and rapid flow of rocky ice. This is due to the "instability of the slopes" in permafrost conditions in the highlands. The instability of slopes in permafrost at elevated temperatures near the freezing point in permafrost warming is associated with effective stress and increased pore water pressure in these soils.
Permafrost development
Jason Kia and his coauthors invented a new filterless hard piezometer (FRP) for measuring pore water pressure in partially frozen soils, such as permafrost warming. They expanded the use of the concept of effective stress for partially frozen soils for use in the analysis of the stability of slopes of warming slopes of permafrost. The application of the concept of effective stress has many advantages, for example, the ability to build foundations and foundations on permafrost soils.
Organic material
In the northern circumpolar region, permafrost contains 1700 billion tons of organic material, which is almost half of all organic. This basin has been created over the millennia and slowly collapses in the cold conditions of the Arctic. The amount of carbon sequestered in permafrost is four times the amount of carbon released into the atmosphere as a result of human activity in modern times.
Effects
The formation of permafrost has significant consequences for ecological systems, primarily due to restrictions imposed on root zones, and also because of restrictions on the geometry of the den and burrows for fauna requiring underground houses. Secondary influences affect species dependent on plants and animals whose habitat is limited by permafrost. One of the most common examples is the prevalence of black spruce in vast areas of permafrost, since this species can tolerate rooting limited to the surface.
Calculations of permafrost soils are sometimes made for the analysis of organic material. One gram of soil from the active layer may contain more than one billion bacterial cells. When placed along each other, bacteria from one kilogram of soil of the active layer form a chain 1000 km long. , 1 1000 . , .
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