Eternally frozen soils: distribution areas, temperature, development features

2024 Author: Henry Conors | [email protected]. Last modified: 2024-02-12 02:40

From this article you will learn about the features of permafrost soils that are common in permafrost zones. In geology, permafrost is land, including stony (cryotic) soil, that is present at a freezing temperature of 0 °C or below for two or more years. Most of the permafrost is located at high latitudes (in and around the Arctic and Antarctic regions), but, for example, in the Alps it is found at higher altitudes.

Ground ice is not always present, as may be the case with non-porous bedrock, but it is often found in quantities in excess of the potential hydraulic saturation of the ground material. Permafrost makes up 0.022% of the total water on Earth and exists in 24% of open land in 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 the currentlevels will be enough to start thawing permafrost in Siberia.

Study

In contrast to the relative paucity of reports on frozen soils in North America prior to World War II, literature on the engineering aspects of permafrost was available in Russian. Beginning in 1942, Simon William Muller delved into relevant literature held by the Library of Congress and the Library of the United States Geological Survey to provide the government with an engineering manual and technical report on permafrost by 1943.

Definition

Permafrost is soil, rock or sediment that has been frozen for more than two consecutive years. In non-ice-covered areas, they exist under a layer of soil, rock, or sediment that 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 with the season, but ranges from 0.3 to 4 meters (shallow along the Arctic coast; deep in southern Siberia and the Qinghai-Tibetan Plateau).

Geography

What about the spread of permafrost? The extent of permafrost varies by climate: today in the Northern Hemisphere, 24% of the ice-free land area - equivalent to 19 million square kilometers - is more or less affected by permafrost.

Slightly more than half of this area is covered with continuous permafrost,about 20 percent is discontinuous permafrost and just under 30 percent is sporadic permafrost. Most of this territory is located in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer, annual permafrost temperature fluctuations become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains temperatures above freezing. 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 suitable for active human life.

Climate

Permafrost usually forms in any climate where the average annual air temperature is below the freezing point of water. Exceptions can be found in wet winter climates, such as in Northern Scandinavia and northeastern Russia west of the Urals, where snow acts as an insulating cover. Glacial areas may be exceptions. Because all glaciers are heated at their bases by geothermal heat, temperate glaciers that are near their pressurized melting point can have liquid water at the boundary with the land. Therefore, they are free from permafrost. "Fossil" cold anomalies in the geothermal gradient in areas where deep permafrost developed during the Pleistocene persist up to several hundred meters. This is evident from well temperature measurements in North America and Europe.

Temperature underground

Typically, the temperature underground varies from season to season less thanair 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 on the north side - creating discontinuous permafrost. Typically, permafrost will remain discontinuous in climates where the average annual soil surface temperature is -5 to 0°C (23 to 32°F). The areas with wet winters mentioned above may not even have intermittent permafrost down to -2 °C (28 °F).

Types of permafrost

Permafrost is often further divided into extensive discontinuous permafrost, where permafrost covers 50 to 90 percent of the landscape and is typically found in areas with mean annual temperatures of -2 to -4 °C (28 to 25 °F), and sporadic permafrost, where permafrost covers less than 50 percent of the landscape and typically occurs at mean annual temperatures between 0 and -2 °C (32 and 28 °F). In soil science, the sporadic permafrost zone is the SPZ, while the extensive discontinuous permafrost zone is the remote sensing zone. Exceptions occur in unglazed Siberia and Alaska, where the current depth of permafrost is a remnant of climate conditions during the Ice Age, where winters were 11 °C (20 °F) colder than today.

Permafrost temperature

When average annual soil surface temperatures are below -5 °C (23 °F), the influence of the aspectcan never be enough to thaw the permafrost and form a continuous permafrost zone (CPZ for short). The line of continuous permafrost in the Northern Hemisphere represents the southernmost boundary where the land is covered by continuous permafrost or glacial ice.

For obvious reasons, designing on permafrost is an extremely difficult task. The line of continuous permafrost is changing north or south around the world due to regional climate change. 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 terrain is subject to melting in the ground. The exposed land of Antarctica is largely permafrost.

Alps

Estimates of the total area of the permafrost zone in the Alps vary greatly. Bockheim and Munro combined the three sources and made tabular estimates by region (3,560,000 km2 in total).

Alpine permafrost in the Andes was not on the map. The extent in this case is modeled to estimate the amount of water in these areas. In 2009, an Alaskan researcher discovered permafrost at 4,700 m (15,400 ft) on Africa's highest peak, Mount Kilimanjaro, about 3° north of the equator. Foundations on permafrost soils in these latitudes are not uncommon.

Frozen seas and frozen bottom

Marine permafrost occurs under the seafloor and exists on polar continental shelvesregions. These regions formed during the last ice age, when most of the Earth's water was locked up in ice sheets on land and sea levels were low. As the ice sheets melted and became sea water again, the permafrost became submerged shelves under relatively warm and s alty boundary conditions compared to the permafrost at the surface. Therefore, underwater permafrost exists under conditions that lead to its decrease. According to Osterkamp, subsea permafrost is a factor in “the design, construction and operation of coastal facilities, seabed structures, artificial islands, subsea pipelines and wells drilled for exploration and production.

Permafrost extends to the depths 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 base reaches 1,493 meters (4,898 ft) in the northern basins of the Lena and Yana rivers in Siberia. The geothermal gradient is the rate of increase in temperature relative to the increase in depth in the Earth's interior. 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 with the thermal conductivity of the geological material and is less for permafrost in soil than in bedrock.

Ice in the soil

When the ice content of permafrost exceeds 250 percent (from ice mass to dry soil), it is classified asmassive ice. Massive icy bodies can range 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 first recorded sightings in North America were made by European scientists on the Canning River in Alaska in 1919. Russian literature gives an earlier date of 1735 and 1739 during the Great Northern Expedition of P. Lassinius and Kh. P. Laptev, respectively. The two categories of massive ground ice are buried surface ice and so-called "intra-shed ice". The creation of any foundations on permafrost requires that there are no large glaciers nearby.

Buried surface ice can come from snow, frozen lake or sea ice, aufeis (rolled river ice) and probably the most common variant is buried glacial ice.

Groundwater freezing

Intradiestimal ice is formed as a result of groundwater freezing. Here, segregation ice prevails, which occurs as a result of crystallization differentiation that occurs during the freezing of wet precipitation. The process is accompanied by water migration to the freezing front.

Intradiestimal (constitutional) ice has been widely observed and studied across 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 geologicalsubstrate. They were first described in 1919.

Carbon cycle

The permafrost carbon cycle is concerned with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to the atmosphere, back to vegetation, and finally back to the permafrost soil through burial and precipitation through cryogenic processes. Some of this carbon is transferred 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, and the transport of carbon between land and water as methane, dissolved organic carbon, dissolved inorganic carbon, inorganic carbon particles, and organic carbon particles.

History

The permafrost of the Arctic has been shrinking over the centuries. The consequence of this is thawing of the soil, which may be weaker, and the release of methane, which contributes to an increase in the rate of global warming in a feedback loop. The distribution areas of permafrost soils have constantly changed in history.

At the last glacial maximum, continuous permafrost covered a much larger area than today. In North America, only a very narrow belt of permafrost existed south of the New Jersey latitude ice sheet in southern Iowa and northern Missouri. 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 a former eternalpermafrost of this period in central Otago and in Argentine Patagonia, but it was probably discontinuous and associated with the tundra. Alpine permafrost also occurred in the Drakensberg during the existence of glaciers above 3,000 meters (9,840 ft). Nevertheless, foundations and foundations on permafrost are being established even there.

Soil structure

Soil can be composed of many substrate materials, including bedrock, sediment, organic matter, water, or ice. Frozen ground is anything below the freezing point of water, whether or not water is present in the substrate. Ground ice is not always present, as may be the case for non-porous bedrock, but it is common and may be present in quantities in excess of the potential hydraulic saturation of the thawed substrate.

As a result, rainfall is increasing, which in turn is weakening and possibly collapsing buildings in areas like Norilsk in northern Russia, which lies in the permafrost zone.

Slope collapse

Over the past century, there have been many reported cases of alpine slope failure in mountain ranges around the world. A large amount of structural damage is expected to be associated with melting permafrost, which is believed to be caused by climate change. Melting permafrost is believed to have contributed to the 1987 Val Pola landslide that killed 22 people in the Italian Alps. Large in mountain rangespart of the structural stability may be due to glaciers and permafrost. As the climate warms, permafrost thaws, leading to less stable mountain structure and eventually more slope failure. Increasing the temperature allows deeper depths of the active layer, which entails even more water penetration. The ice in the soil melts, causing loss of soil strength, accelerated movement, and potential debris flows. Therefore, construction on permafrost is highly undesirable.

There is also information about massive falls of rocks and ice (up to 11.8 million m³), earthquakes (up to 3.9 million miles), floods (up to 7, 8 million m³ of water) and the rapid flow of rocky ice. This is caused by "slope instability" in permafrost conditions in the highlands. Slope instability in permafrost at elevated temperatures near freezing in warming permafrost is associated with effective stress and increased pore water pressure in these soils.

Development of permafrost soils

Jason Kea and co-authors have invented a new filterless rigid piezometer (FRP) to measure pore water pressure in partially frozen soils such as warming permafrost. They extended the use of the concept of effective stress to partially frozen soils for use in slope stability analysis of warming permafrost slopes. The application of the concept of effective stress has many advantages, for example, the ability to build bases and foundations onpermafrost soils.

Organic

In the northern circumpolar region, permafrost contains 1,700 billion tons of organic material, nearly half of all organic matter. This basin has been created over millennia and is slowly being destroyed 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 by human activity in modern times.

Consequences

The formation of permafrost has significant implications for ecological systems, primarily due to restrictions placed on root zones, as well as restrictions on the geometry of dens and burrows for fauna requiring underground homes. Secondary impacts 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, as this species can tolerate establishment that is limited near the surface.

Calculations of permafrost soils are sometimes made for the analysis of organic material. One gram of soil from an active layer can contain over 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. The number of bacteria in permafrost soil varies widely, typically between 1 and 1000 million per gram of soil. Most of thesebacteria and fungi in permafrost soil cannot be cultured in the laboratory, but the identity of microorganisms can be revealed using DNA-based methods.

The Arctic region and global warming

The Arctic region is one of the natural sources of methane greenhouse gases. Global warming is accelerating its release. A large amount of methane is stored in the Arctic in natural gas deposits, permafrost and in the form of underwater clathrates. Other sources of methane include submarine taliks, river transport, ice complex retreat, submarine permafrost, and decaying gas hydrate deposits. Preliminary computer analysis indicates that permafrost can produce carbon equal to about 15 percent of today's emissions from human activity. Warming and thawing of soil massifs makes building on permafrost even more dangerous.