Tundra terrain covers a significant portion of the Earth’s surface, primarily in its northern reaches. This environment is characterized by extreme cold and harsh conditions. Its treeless plains are shaped by freezing and thawing. Tundra plays a role in global climate systems and supports specialized ecosystems.
Defining Tundra Terrain
Tundra terrain is defined by consistently low temperatures, a short growing season, and the absence of tall trees. Average winter temperatures can drop to around -28°C (-18°F), while summer temperatures might rise to about 12°C (54°F). This limited warmth restricts plant life to dwarf shrubs, sedges, grasses, mosses, and lichens, with scattered trees appearing only in some regions.
Three primary types of tundra exist globally. Arctic tundra, found in the far Northern Hemisphere, encircles the North Pole and extends south to coniferous forests. It is known for its cold, desert-like conditions and deep permafrost. Alpine tundra is located on mountains worldwide at high altitudes, where low air temperatures prevent tree growth. Unlike Arctic tundra, alpine soils are better drained. Antarctic tundra is found in the Southern Hemisphere, mainly on islands near Antarctica and some coastal regions of the continent, characterized by even lower temperatures and sparser vegetation.
Distinctive Terrain Features
The tundra landscape is marked by unique geological features, sculpted by constant freeze-thaw cycles and permafrost. Patterned ground refers to distinct, often symmetrical geometric shapes formed by ground material deformation. These patterns, including circles, polygons, nets, steps, and stripes, are created as the ground repeatedly freezes and thaws, sorting soil and stones. Sorted circles, for instance, often have fine-grained material in the center surrounded by larger stones.
Polygonal ground, a common form of patterned ground, consists of hexagonal or octagonal shapes ranging from a few meters to over 100 meters in diameter. These polygons often form due to thermal contraction cracking of the soil, especially in areas with continuous permafrost, where cracks develop and can fill with ice to form ice wedges. Solifluction lobes are another feature, representing slow, downhill movement of saturated soil and vegetation, appearing as tongue-shaped or terrace-like formations on slopes. This movement is influenced by the viscous flow of the thawed active layer over the frozen ground.
Pingos are isolated, conical mounds of earth with an ice core, found in permafrost regions. They form when water beneath the surface freezes and expands, pushing up the overlying soil. Thermokarst formations, such as thaw lakes and slumped terrain, result from the thawing of ice-rich permafrost. When ground ice melts, the surface can collapse, creating depressions that may fill with water to form thermokarst lakes, or leading to ground subsidence and slumping on slopes.
Permafrost: The Foundation of Tundra Terrain
Permafrost is ground that remains frozen for at least two consecutive years, forming a significant component of tundra terrain. This permanently frozen layer can consist of soil, rock, and various forms of ice, including wedge-shaped ice formations and lens-shaped masses. The depth and distribution of permafrost vary, with continuous permafrost found in regions where the mean annual temperature is well below freezing, while discontinuous or sporadic permafrost occurs in areas with slightly warmer average temperatures.
Above the permafrost lies the active layer, the uppermost section of soil that thaws during warmer summer months and refreezes in autumn. Its thickness can vary seasonally and geographically, ranging from a few centimeters to several meters. Permafrost profoundly influences water drainage; water cannot penetrate the frozen layer, remaining on the surface. This leads to widespread boggy conditions, marshes, and numerous shallow lakes during the summer thaw.
Permafrost also plays a significant role in soil stability and landscape morphology. The frozen ground provides a stable foundation, but restricts the development of deep root systems in vegetation. Ground stability is directly linked to the permafrost’s thermal state, and temperature changes can significantly impact its ability to support overlying soil and structures.
Responding to a Warming Climate
Tundra terrain is experiencing significant physical changes due to a warming climate, particularly permafrost thaw. Temperatures across the Arctic are increasing two to four times faster than the global average, leading to widespread permafrost degradation. This warming causes the frozen ground to thaw, often leading to a loss of ground stability and landscape alterations.
One observable change is increased thermokarst activity, where melting ground ice causes the land surface to collapse. This process can result in new thermokarst lakes, which are depressions filled with water, and widespread slumps where sections of terrain slide or collapse. These changes can drastically alter local drainage patterns, as water is attracted to newly formed depressions, potentially leading to drier elevated areas and wetter low-lying zones.
Coastal erosion is also accelerating in tundra regions, particularly along permafrost coasts, as the frozen ground stabilizing shorelines thaws and becomes more susceptible to wave action. Shoreline retreat rates in some areas, such as the Canadian Beaufort Sea, have been documented as high as -46 meters per year. The physical impacts of thawing permafrost extend to infrastructure, with buildings, roads, and pipelines facing increased risks of damage due to ground subsidence and uneven surface deformations. As the ground loses its load-bearing capacity, structures built on permafrost can settle unevenly, leading to significant structural challenges.