Description of the phenomena
Common frost heaving
Frost heave is the process by which the freezing of water- saturatedIce lenses in tundra
Frost heave is common in arctic tundra because the permafrost maintains ground frozen at depth and prevents snowmelt and rain from draining. As a result, conditions are optimal for deep ice lens formation with large ice accumulations and significant soil displacement. Differential frost heave producing complex patterns will occur if the correct conditions exist. Feedback from one year's frost heave influences the effects in subsequent years. For example, a small increase in overburden will affect the depth of ice formation and heaving in the subsequent years. Time-dependent models of the frost heave indicate that over a long enough period the short-separation perturbations damp out, while mid-range perturbations grow and come to dominate the landscape.Subglacial ice formations
Bands of sediment orUnderstanding the phenomena
200px, Ice lenses are responsible for (picture) growth">palsa (picture) growth The basic condition for ice segregation and frost heaving is existence of a region in soil or porous rock which is relatively permeable, is in a temperature range which allows the coexistence of ice and water (in a premelted state), and has a temperature gradient across the region. A key phenomenon for understanding ice segregation in soil or porous rock (also referred to as an ice lens due to its shape) is premelting, which is the development of a liquid film on surfaces and interfaces at temperatures significantly below their bulk melting temperature. The term premelting is used to describe the reduction in the melting temperature (below 0 °C) which results from the surface curvature of water that's confined in a porous medium (the Gibbs-Thomson effect). Premelted water exists as a thin layer on the surface of ice. Under premelting conditions, ice and water can coexist at temperatures below -10 °C in a porous medium. The Gibbs-Thomson effect results in water migrating down a thermal gradient (from higher temperatures to lower temperatures); Dash states, “…material is carried to colder regions…” This can also be viewed energetically as favoring larger ice particles over smaller ( Ostwald ripening). As a result, when conditions exist for ice segregation (ice lens formation) water flows toward the segregated ice and freezes on the surface, thickening the segregated ice layer. It is possible to develop analytic models using these principles; they predict the following characteristics, which are consistent with field observations: * Ice forms in layers which are parallel to the overlying surface. * The ice initially forms with small microfractures parallel to the surface. As ice accumulates the ice layer grows outward in what is frequently characterized as an ice-lens parallel to the surface. * Ice will form in water-permeable rock in much the same way as it forms in soil. *If the ice layer resulted from a cooling from a single direction (e.g., the top) the fracture tends to lie close to the surface (e.g., 1–2 cm in chalk). If the ice layer results from freezing from both sides (e.g., above and below) the fracture tends to lie deeper (e.g., 2–3.5 cm in chalk). * Ice forms rapidly when liquid is readily available. When liquid is readily available, the segregated ice (ice lens) grows parallel to the exposed cold surface. It grows rapidly until the heat liberated by freezing warms the ice lens boundary, reducing the temperature gradient and controlling the rate of further ice segregation. Under these conditions, ice grows in a single layer which gets progressively thicker. The surface is displaced and soil repositioned or rock fractured. * Ice forms in a different pattern when liquid is less readily available. When liquid is not readily available, the segregated ice (ice lens) grows slowly. The heat liberated by freezing is unable to warm the ice lens boundary. Hence the area through which the water is diffusing continues to cool until another ice segregation layer forms below the first layer. With sustained cold weather, this process can repeat, producing multiple ice layers (ice lenses), all parallel to the surface. The formation of multiple layers (multiple lenses) producing more extensive frost damage within rocks or soils. * No ice forms under some conditions. At higher overburden pressures and at relatively warm surface temperatures, ice segregation cannot occur; the liquid present freezes within the pore space, with no bulk ice segregation and no measurable surface deformation or frost damage.Ice lens growth in rock
Rocks routinely contain pores of varying size and shape, regardless of origin or location. Rock voids are essentially small cracks, and serve as the location from which a crack can propagate if the rock is placed in tension. If ice accumulates in a pore asymmetrically, the ice will place the rock in tension in a plane perpendicular to the ice accumulation direction. Hence the rock will crack along a plane perpendicular to the direction of ice accumulation, which is effectively parallel to the surface. Walder and Hallet developed models that predict rock crack-growth locations and rates consistent with fractures actually observed in the field. Their model predicted that marble and granite grow cracks most effectively when the temperatures range from a −4 °C to −15 °C; in this range granite may develop fractures enclosing ice 3 meters in length in a year. When the temperature is higher the ice which is formed does not apply enough pressure to cause the crack to propagate. When the temperature is below this range the water is less mobile and cracks grow more slowly. Mutron confirmed that ice initially forms in pores and creates small microfractures parallel to the surface. As ice accumulates, the ice layer grows outward in what is frequently characterized as an ice-lens parallel to the surface. Ice will form in water-permeable rock in much the same way as it forms in soil. If the ice layer resulted from cooling from a single direction (e.g., the top) the rock fracture tends to lie close to the surface (e.g., 1–2 cm in chalk). If the ice layer results from freezing from both sides (e.g., above and below) the rock fracture tends to lie deeper (e.g., 2–3.5 cm in chalk).Ice sphere formation
The formation of an ice sphere can happen when an object is about 0.5–1.0 ft above where the water reaches repeatedly. The water will form a thin layer of ice on any surface it reaches. Each wave is an advancement and recession of water. The advancement soaks everything on the shore. When the wave recedes, it's left exposed to freezing temperatures. This brief moment of exposure causes a thin layer of ice to form. When that formation is suspended in the air by dead vegetation or erect objects, the ice will begin to form a sphere or teardrop-like shape. Similar to how aReferences
{{Periglacial environment Glaciology Erosion landforms Permafrost