Types of Ice

Found on the ground, needle ice is composed of thin ice crystals. The crystals grow upwards from as little as a few centimeters underground (NSIDC 2011). To form needle ice, or ribbon ice, is the presence of flowing ground water that contacts freezing air is required. Typically it is formed over night when air temperatures drop and on generously sloping ground where there is water movement. Sizes of ice needles can range from one centimeter to 40 centimeters in length, under ideal conditions. As the needles grow, the surface becomes more available to wind and water erosion.

Freeze and thawing of periglacial, arctic ground over many hundreds of years forms ice wedging processes that result in drastic landscape changes. Permafrost soils are located just below the active layer of top soil. The process begins with cold winter temperatures causing the active layer of soil to shrink above the permafrost, thus causing cracks to form. During the warmer days of spring, water seeps into the cracks, is chilled by the frozen permafrost layer and expands to form wedges of ice in the soil. When summer temperatures arrive, the topmost layers of the ice wedges melt. The cycle continues with the continuing change of seasons, with each winter the cracks form in the already compromised soil; enlarging the ice wedges every year. As shown in the diagram above, eventually this ice wedges become large enough to form dramatic landscapes. A complete animation of the process can be viewed at the Arctic National Wildlife Refuge webpage.

Segregated ice forms each winter in the active layer of soil and builds ontop of permafrost. These bodies of pure ice are seen as lenses, veins, or wedges. These ice bodies are formed from the mutual attraction of liquid water and vapor to the lower cold vapor pressure in the freezing plane of the soil. Soil permeability and porosity provide optimal storage and diffusion of the water throughout the soil body. As shown in the diagram above, the ice bodies build upon each other and during the cyclic seasons, soil becomes displaced by upward movement, frost heave - or is assimiliated into the lower permafrost.

Frost heave is a physical weathering process, a form of frost action, occuring from freeze and thaw events. When ice is formed within soil, it can generate extreme force on its surroundings and cause frost heaving. The "heave" refers to upward movement of the ground surface in response to freeze / thaw processes. Frost heaving of the soil was once believed as a result only from the expansion of water on freezing surfaces. The concept of frost heave includes growing ice crystals underground drawing water from the surrounding soil that develops into ice lenses (Penner 1962). The diagram provided above, shows the concept in relation to an asphalt ground structure (road) and the formation of ice lenses breaking apart the asphalt. The large arrow on the diagram indicates the pressure upwards of the ice lenses on the surface. The dynamics of freezing form an intricate process, however, only three things are required to produce a frost heave incident: freezing temperatures, the "right" kind of soil and an abundant water supply (Manz 2011).

The National Snow and Ice Data Center describes patterned ground as any ground surface that exhibits a discernible ordered, more-or-less symmetrical, morphological pattern of ground and, where present, vegetation. Types of patterned ground are varied and are dependent on organic material present, mineral content of soil, location and water/wind relationships. Patterned ground conditions are a naturally occuring phenomenon that produces stunning landforms often as a direct result of frost heave processes. The types of patterned ground formations can be organized into circles, polygons, nets, steps and stripes. Field studies conducted in northern Alaska have provided a classification of arctic soils and patterns; providing typical soil classification based on pattern types (Tedrow and Drew,1958). For further information regarding arctic soils and their classification: find the article here.

Patterned ground is described into two categories: sorted and non-sorted. This is true whether the ground pattern exhibits polygons, circles, nets or stripes. Sorted landforms will show a definitive ring or margin of stones/rocks. Non-sorted landforms will lack the stone margins and will exhibit some marginal vegetation .

Sizes of sorted or non-sorted circles may appear as small as 1.5 feet to over 10 feet in diameter (USACE 2012). The circles are commonly dome shaped with small polygonal cracks throughout when active. After periods of inactivity, vegetation will begin to grow within the circles. Typically, these are found on flat terrain. If the surface is on a steep slope, elongation will occur creating stripes.

Sorted circles: Sorted landforms will show a definitive ring or margin of stones/rocks.
Photographed in Kvadehukken, Svalbard.
Photo credit: Ina Timling, Geophysical Institute
University of Alaska Fairbanks

Non-sorted circles: Non-sorted landforms will lack the stone margins and will exhibit some marginal vegetation.
Photographed in Kvadehukken, Svalbard.
Photo credit: Ina Timling, Geophysical Institute
University of Alaska Fairbanks

Polygons

Polygons can be found on display as on a micro-scale of less than seven feet diameter or on a macro-scale of 50 to 100 feet diameters (USACE 2012). Polygon patterns of frozen ground will display the sorted or non-sorted features in both the micro and macro scales. Ice wedge polygons are honeycomb formations of ice formed under the surface and extend deep below the surface. They will display with cracks at the margins or with furrows, deppressions of vegetation. Polygons can be further classified into low-centered or high-centered, referring to depressions or mounds, respectively.

Low centered polygons featuring irregular ice wedge patterns.
Sagavanirktok river delta, Alaska.
Copyright © 2012 Permafrost Laboratory.

Nets

Sorted and non-sorted nets are similar to polygons and circles..
Display will have vegetation intersperssed throughout "net-like" stones...appears hummocky.
Photo credit: Ronald Daanen, Geophysical Institute
University of Alaska Fairbanks

Steps

Steps are formed from parent landform features of circles, polygons and nets on mountain hillsides in periglacial climates.
The parent landform will appear to be sorted or non-sorted.
Glacier National Park, Montana.Gable Mountain, viewed from Lee Ridge.
USGS - Carrara July 25, 1984.

Stripes

Stripes display as vertical landforms down slopes/hillsides.
Like steps, the parent features will be non-sorted circles and polygons or sorted circles, polygons, and nets.
Dracoisen, Ny Friesland - Svalbard
Photo credit: Glaciers Online, M. Hambrey

Return to the beginning.

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Conclusion

Processes at work to create frozen ground and subsequent land formations are varied yet simplistic in understanding. The actual mechanics of frozen ground movements however are complex. Contributions of available water to site specific soil types will produce dramaitcally different results as the mineralogical content of the soil varies. Take into account precipitation events that would provide additional thermal heat, the processes at work are phenomenal. The unlimited number of variables in frozen ground patterns are diverse and therefore an unpredictalce science, however, general conclusions can be made based on soil types. Identification of general soil types in an area displaying specfic ground pattern landforms therefore can be made. Understanding the processes of frozen ground formations can also lead to monitoring climate change effects by observing changes in the land features. Determining a base research site, or sites, for such observations are critical in determining climate change effects on mountain regions.

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Short Video

Video produced and edited by April Courtney Dec 2011

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References