Iinfluence On Infrastructure
Introduction. More than 60% of the Russian territory is located in permafrost regions. Several large cities (Yakutsk, Noril'sk, Vorkuta) with populations of more than a hundred thousand and large river ports are built upon permafrost. The ability of permafrost to support buildings upon it (the bearing capacity) decreases with warming. The foundations are designed with a construction-specific safety factor, which in the practice of the cold-region engineering varies from 5% to 60% with respect to the bearing capacity, and is typically 20% for the most of the residential buildings in the Russian northern cities. Warming of permafrost and decrease of the bearing capacity beyond the safety range may seriously affect the constructions upon it, ultimately leading to damage.
The Russian North is industrially well developed. In the context of changing climate, the infrastructure of the oil and gas industry is of particular concern, because of its economic importance and potential environmental threats associated with the oil spills. Extracting facilities, pump stations and pipelines are affected by the geomorphological processes that involve various forms of mass movement of thawing material and ground settlement due to thermokarst. Many such processes have been favored under the warmer climatic conditions of the last decade. The annual number of accidents on the 350 thousand km long network of pipelines in West Siberia totals 35 000. About 21% of the reported accidents are caused by mechanical damage to the pipelines due to increased strength, deformation, and weakening of the foundations anchored in permafrost, and are thus very likely to be related to climatic change, warming, and thawing of the frozen ground.
A survey in the Russian northern cities indicated that in 1992 the percentage of damaged buildings was 10% in Norilsk, 22% in Tiksi, 35% in Dudinka and Dikson, 50% in Pevek and Amderma, 55% in Magadan, 60% in Chita, and 80% in Vorkuta (37). In the period from 1990 to 1999 the rate of reported damage to buildings increased by 42% in Norilsk, 61% in Yakutsk, and 90% in Amderma. There is still a debate whether the climate change or improper design of the construction, leaking sewage, and other similar anthropogenic influences are responsible for the current dramatic situation in the Russian North. Obviously, there is a combination of the acting factors, but the buildings are ultimately damaged due to the weakening of permafrost underneath them. As global warming continues to evolve, it may produce similar impacts on structures throughout the circumpolar permafrost regions, even under appropriate practices of environmental management.
The northern zone of high hazard potential includes the Russian Arctic coast from the Kara Sea on the west to the Chukchi Sea on the East. River terminals in Salekhard, Igarka, Dudinka, and Tiksi fall within this zone. It spreads deep into the continent in central Siberia and Yakutia. These regions are underlain by continuous permafrost, which will not change noticeably in areal extent; the main effect will be warming and deeper seasonal thawing of the frozen ground, which may exceed the safety limits incorporated in the design of the constructions. Such changes are potentially dangerous for the pre-existing structures, whereas the design, foundations, and managing practices of the newly constructed buildings may be adjusted to changing permafrost properties. Particular concerns are associated with the Yamal Peninsula, which was periodically flooded during the ocean transgressions in the geological past. Due to the presence of salt in the deposits the thawing/freezing point is lowered. Permafrost here is in delicate balance with climate and may become unstable even under a slight climatic variation.
Most of the central part of the Russian permafrost falls into the zone of moderate hazard potential, while large areas in southern Yakutia and in central Siberia between the Ob and Yenisey rivers will have low susceptibility to climate-induced permafrost hazards.
According to one of an opinion, many problems of stability of constructions in the North of Russia are mostly caused by default of operational conditions than by climate change. It is partly so, but it is necessary to take into account that the final reason of damage or destruction of buildings in permafrost regions is a weakening of foundations. Such a weakening is due to decreasing of permafrost bearing capacity, whether it is caused by outflow of water, soil mineralization or climate change. Thus, even considering the influence of operational mistakes, the modern situation can be regarded as a possible model of the future under climate warming with keeping of all operational norms. It is necessary to note that similar problems are typical for other northern countries, e.g. for USA (Alaska) and the north of Canada where operational requirements are carried out much more strictly, than in Russia.
Periglacial landforms can be subdivided into two main groups: slope landforms and patterned ground landforms. Slope landforms include cryoplanation terraces, gelifluction terraces, and cryopediments. These slope landforms are similar to slope landforms found in other warmer, semi-arid environments. Patterned ground landforms include thermokarsts, pingos, palsas, earth hummocks, and polygonal ground. Most of the patterned ground landforms are completely unique to the periglacial environment. All of the slope landforms and some of the patterned ground landforms can be observed in the Copper River watershed. Some of the major slope and patterned ground landforms are described below.
Cryoplanation terraces are erosional surfaces caused by freeze-thaw activity. Cryoplanation terraces are composed of risers (i.e., vertical or steeply sloped surfaces in step-like landforms) and treads (i.e., flat or gently sloped surfaces in step-like landforms). Soils tend to be increasingly well-developed from the toeslopes of the risers to the far-reaches of the treads. Soils on the toeslopes of the risers tend be poorly to undeveloped, the materials typically having been recently deposited. Risers, themselves, tend to be too steep and/or unweathered to support any soil at all. Soils on the treads tend to be transport limited and better developed with distance from the riser.
Gelifluction is the slow, down-slope movement of waterlogged soils which typically occurs where permafrost restricts drainage and frost heave of the overlying waterlogged soils initiates slow, down-slope movement. Gelifluction terraces typically occur where local relief is so great that large lobes of waterlogged soils can move relatively rapidly down slope, creating steep terrace risers on their down-slope edges. Tread slopes range from 3 to 25 percent, and risers may be as high as 4 m. Sections cut through gelifluction terraces may show buried organic and mineral soil layers over-ridden by the gelifluction lobes.
Cryopediments are gently-sloped surfaces in footslope and toeslope positions, and range in size from local features covering tens of m2 to regional features such as the 50,000 km2 Old Crow Pediments in northern Yukon. Cryopediments are erosion and transport surfaces, with sheet wash and gelifluction being the dominant erosion and transport processes. Cryopediments, like most footslope and toeslope positions, are gently concaved and support integrated drainage systems. With the exception of gelifluction, cryopediments are similar to other pediment features in other warmer, semi-arid environments.
Patterned Ground Landforms
Thermokarst is a general term that refers to the many landforms that develop in response to the melting of ground ice. Thawing permafrost creates uneven surfaces that primarily consist of subsidence features that collect water such as collapse scar bogs and small thermokarst lakes. Two cases are presented to demonstrate the development of thermokarst features.
In one case massive ice wedges thaw, perhaps in response to climate change or a change in vegetative cover. High-centered polygons, which are described below, begin to develop, separated by troughs over the melting massive ice wedges. The troughs collect water during the summer, thereby intensifying the melting. Eventually, enough of the ice melts that the entire area subsides. In another case a regional ground water flow system develops, perhaps on a glaciofluvial fan. Ground water is recharged on the high fan, warmed at depth, and discharged on the low fan. The discharge of the warm, regional ground water locally melts the permafrost and the entire area subsides. In both cases, water collects in the large subsidence features and either a collapse scar bog or a thermokarst lake develops.
Pingos are conical, ice-cored earthen mounds or hills, that may be 400 m in diameter and 70 m in height, that form where massive ice accumulates near the ground surface. There are two types of pingos: closed-system and open-system. Closed system pingos tend to form on plains in the continuous permafrost zone where permafrost is shallow and severe winter cold causes intense frost action in the active layer. As the active layer freezes, it expands, and high hydraulic pressures are created between the seasonal frost and the permafrost. The high hydraulic pressures force water to move laterally to where it is forced toward the ground surface. As the water approaches the surface, it freezes and forms a conical, ice-cored earthen mound or hill. Open-system pingos tend to form on gently sloping surfaces in the discontinuous permafrost zone. Regional ground water from beneath the permafrost discharges to the surface under high hydraulic pressures. Again, as the water approaches the surface, it freezes and forms a conical, ice-cored earthen mound or hill. Typically, the tip of the cone, with a high surface area to volume ratio, melts in the summer and collapses, creating a volcano-like appearance.
Palsas are ice-cored peat hummocks, that may be 50 m in diameter and 7 m in height, that form where massive ice accumulates near the ground surface. Palsas form where wind blows snow off a portion of a peat bog allowing intense frost action to penetrate deeply. As the ice freezes locally, it expands, and a mound develops. This mound protrudes above the peat bog surface and is more likely to be blown clear of snow in subsequent winters, creating a positive feedback that enlarges the feature.
Earth hummocks are domed, non-sorted circles, that may be 1.5 m in diameter and 0.8 m in height. Earth hummocks result from the downward movement of soil in depressions and the upward movement of soil in mounds, but the specific processes involved are poorly understood. In permafrost areas, freeze-thaw of ice lenses at the top and bottom of the active layer may produce gravity-induced, cell-like movements since the tops and bottoms of the freeze-thaw zone have opposite curvature. However, earth hummocks develop in non-permafrost areas, too, and no adequate processes for their development have been proposed.
Polygonal ground refers to cell-like, surface microrelief features 3-30 m in diameter, that form over massive ice wedges in the shallow subsurface. Massive ice wedges tend to be vertical, although they may appear to be horizontal when seen in transverse cross-section. These ice wedges form polygonal networks in the shallow subsurface that are reflected in the conspicuous polygonal microrelief features on the surface. There are low-centered and high-centered polygons. Low-centered polygons form where actively growing massive ice wedges upturn surface deposits, resulting in low earthen walls that surround the cells. High-centered polygons form where actively melting ice wedges result in shallow troughs that surround the cells.
Cryoturbation is the mixing of soil due to intense frost action. The effects of cryoturbation are varied, and include the disruption of soil horizons and the incorporation of coarse fragments of organic matter into the lower portions of the active layer. The net effect is that soil profiles can be quite complex, and it can be difficult to infer pedogenic histories and processes
An ice wedge is a crack in the ground formed by a narrow or thin piece of ice that measures anywhere from 3 to 4 meters wide and extends downwards into the ground up to 10 inches. During the winter months, the water in the ground freezes and expands. Once temperatures reach -17 degrees Celsius or colder, the ice that has already formed acts like a solid and contracts to form cracks in the surface known as ice wedges. As this process continues over many years, ice wedges can grow up to the size of a swimming pool.
The origin of ice wedges has many theories but only one has consistently been backed by most prominent scientists: the thermal contraction theory.
The Thermal Contraction Theory states that during the winter months, thermal contraction cracks form only a few centimeters wide and a couple meters deep because of the extreme cold. Over the next few, the snow melts and the remaining water fills the cracks and the permafrost below the surface freezes it. These tiny cracks turn into permafrost. Once the summer months arrive, the permafrost expands; the fact of horizontal compression produces upturning of the frozen sediment by plastic deformation. The next winter the cold refreezes and cracks the already forming ice wedge and opens way for the eventual melting snow to fill the empty crack. The mean annual air temperature thought needed to form ice wedges is -6° to -8° C or colder.
There are three different forms of ice wedges: Active, Inactive and Ice Wedge Casts. All three forms are prevalent today and can be found in different parts of the world.
Active ice wedges are those that are still evolving and growing. During each year, a layer of ice will be added if cracking occurs, but cracking need not occur every year to be considered active. The zone in which most ice wedges remain active is along the permafrost zone. The amount of active ice wedges that is cracking yearly is consistently declining and becoming inactive.
Inactive ice wedges are wedges that are no longer cracking and growing. Throughout the winter months, the wedge does not split and therefore in the summer no new water is added.
In areas of past permafrost, ice wedges have melted and are no longer filled with ice. The wedge, which is now empty, is filled with sediment and dirt from the surrounding walls. These are called ice wedge casts and are used to calculate the climate of hundreds of thousands of years ago.
Ice wedges can tell a very great deal about history. After a while, when the ice wedge gets large enough and is no longer active, sediments will fill the crack left by the ice wedges. These, in turn, are called pseudomorphs and could contain important hints of the past, including animal remains.
Frost heaving (or frost heave) occurs when soil expands and contracts due to freezing and thawing. This process can damage plant roots through breaking or desiccation, cause cracks in pavement, and damage the foundations of buildings, even below the frost line. Moist, fine-grained soil at certain temperatures is most susceptible to frost heaving.
Originally, frost heaving was thought to occur due simply to the freezing of water in soil. However, the vertical displacement of soil in frost heaving can be significantly greater than the expansion that occurs when ice freezes. In the 1960s, frost heaving was demonstrated in soil saturated in benzene and nitrobenzene, which contract when they freeze.
Frost creep, an effect of frost heave, involves a freeze-thaw action allowing mass movement down slope. The soil or sediment is frozen and in the process moved upward perpendicular to the slope. When thaw occurs the sediment moves downwards thus mass movement occurs.
The current understanding is that certain soil particles have a high affinity for liquid water. As the liquid water around them freezes, these soils draw in liquid water from the unfrozen soils around them. If the air temperature is below freezing but relatively stable, the heat of fusion from the water that freezes can cause the temperature gradient in the soil to remain constant. The soil at the point where freezing is occurring continues to draw in liquid water from the soils below it, which then freezes and builds up into an "ice lens". Depending on the soil's affinity for moisture and amount of moisture available, a significant amount of soil displacement can result.
The earliest known documentation of frost heaving came in the 1600s.
Three conditions are generally necessary for frost heaving to occur:
- freezing temperatures
- a supply of water
- a soil that has:
- the ability to conduct water
- a high affinity for water
- saturation (i.e. the pore spaces are filled with water)
Silty and loamy soil types are susceptible to frost heaving. The affinity of a soil for water is generally related to the surface area of the particles that it is composed of. Clays have a high ratio of surface area to volume and have a high affinity for water. Larger particles like sand have a lower ratio of surface area to volume and therefore a low affinity for water.
Conversely, the hydraulic conductivity of a soil is related to the pore size. Soils composed of very small particles like clay have small pores and therefore low hydraulic conductivity. Soils composed of larger particles like sand have larger pores and a higher hydraulic conductivity.
The offsetting nature of these two requirements mean that clayey and sandy soils are less conducive to frost heaving than silt, which has a moderate pore size and moisture affinity.
Frost creep, an effect of frost heave, involves a freeze-thaw action allowing mass movement down slope. The soil or sediment is frozen and in the process moved upward perpendicular to the slope. When thaw occurs the sediment moves downwards thus mass movement, or locomotion, occurs.
In Arctic regions, frost heaving for hundreds of years can create structures, known as pingos, as high as 60 metres. Frost heaving is also responsible for creating stones in unique shapes such as circles, polygons and stripes. A notable example is the remarkably circular stones of the islands of Spitsbergen.
Polygonal forms caused by frost heave have been observed in near-polar regions of Mars by the high-resolution HiRISE camera on the Mars Reconnaissance Orbiter. In May 2008 the Mars Phoenix lander touched down on such a polygonal frost-heave landscape and quickly discovered ice a few centimetres below the surface.
Thermokarst refers to a land surface that forms as ice-rich permafrost thaws. It occurs extensively in Arctic areas, and on a smaller scale in mountainous areas such as the Himalayas and the Swiss Alps.
The name is given to very irregular surfaces of marshy hollows and small hummocks. These pitted surfaces resemble those formed by solution in some karst areas of limestone, which is how they came to have karst attached to their name without the presence of any limestone. Small domes that form on the surface due to frost heaving with the onset of winter are only temporary features. They then collapse with the arrival of next summer's thaw and leave a small surface depression. Some ice lenses grow and form larger surface hummocks, which last many years and sometimes become covered with grasses and sedges, until they begin to thaw. These domed surfaces eventually collapse either annually or after longer periods and form depressions which contribute to uneven surfaces. These are included within the general label of thermokarst.
In areas underlain by permafrost, these depressions are usually occupied by a thermokarst lake (also called thaw lake), as the meltwater cannot drain away. Even small surface irregularities can start thermokarst processes and create thermokarst lakes. Water initially pools in a depression and its presence begins to thaw the permafrost beneath. As thaw continues along lake margins, the lake extends. Thaw extension continues until intervening higher ground is breached, interconnecting different lakes and eventually creating an outlet channel. In recent years, thermokarst lakes have become increasingly common in Siberia and other tundra environments. This permafrost thawing releases carbon dioxide and methane gase.
Thaw or thermokarst pits occur in areas underlain by permafrost containing large masses of ground ice. If the ground surface is disturbed above a large ice mass the resultant change in the thermal regime can cause the ice mass to thaw; this thawing causes a thaw pit to form . The occurrence of these pits indicates poorly drained, fine-grained sediments with the permafrost table near the surface.
Apart from ice-rich permafrost, there are additional environments which may give rise to thermokarst terrain. One of those is a proglacial outwash plain which may lead to the formation of glacial thermokarst, where kettle-holes result from the thawing of fossil ice blocks overlain by moraines. Another environment are floodplains which in cold climates may be covered by large amounts of ice-rich sediment, for example after an ice-dammed lake drains in a catastrophic event. Subsequent melting of the ice contained in the sediments then results in alluvial or fluvial thermokarst.
Solifluction sheets and lobes are masses of unconsolidated sediment that range from less than a foot to hundreds of feet in width. These features are extensive in the arctic and may cover entire valley walls. They occur on slopes as low as 3°. Solifluction the plays a major role in the formation of patterned ground. This type of patterned ground is formed by the gradual downslope (gravity) movement of waterin saturated sediments. The surficial materials are especially mobile in the permafrost region because the active layer commonly is supersaturated with moisture. This condition is caused by the impermeability of the underlying permafrost and by the low evaporation rate. Downslope movements of solifluction features are so rapid that a structure resting upon one will either be subjected to large earth pressures or will move passively downslope.