The stripes are marked by alternate belts of coarse and finer debris. The coarse material collects in the furrows while finer debris forms ridges. The furrows are about 75 cm deep. The coarse stripes may be as wide as 1.5 meters. The finer stripes are two to four times the width of the coarser ones. Sometimes the stripes extend continuously for 100 meters or so.
Steps and Terraces:
Steps or stone-banked terraces occur on sloping surface (10 to 25 degrees) but the slopes are gentler than in the case of stripes. They are transverse to the slope or parallel to contours. When they are elongated down-slope into lobes, they are called garlands. The treads of the steps or lobes or garlands consist usually of finer material and have slopes of 2 to 3 degrees. The risers may be as high as 5 meters. The treads may extend up to 30 meters along the slope.
Causes of Stripes and Steps:
The cause of these features is believed to be solifluction. The stripes and terraces are believed to be caused by the downslope movement of soil masses as lobes of a moistened debris over impervious permafrost zone. The freeze-thaw action also encourages downslope migration of individual particles. The action of solifluction is manifest in the stripes of alternating parallel coarse and finer material. They are modified sorted polygons and circles pulled down and elongated by solifluction processes.
The steps and terraces are also believed to be associated with solifluction particularly on slopes in tundra regions. The vegetation-turf-or peat-covered ground is rendered into risers, and treads are caused by the movement of soil masses on slopes.
Where permafrost has degraded due to increase of temperature the surface is converted into undulations. The pockets of pure ice in the permafrost melt, giving such topographic expression. This phenomenon is known as Thermokarst. In the areas of thermokarst one particular type of patterned ground develops. It is known as ‘string bogs’. Steps or undulation axes are transverse to slope. They are found in cold coniferous forest zones and are believed to be associated with the cracking of surface on the thawing of frozen ground, or solifluction processes. The ridges or ‘ups’ are dry but the intervening depressions are waterlogged.
As noted earlier polygons, circles and nets occur in flat ground with slope less than 2°. Steps and stripes are found on slopes ranging from about 6° to 30°, the stripes occurring on steeper slopes than steps. Slopes more than 30° are too steep for the development of patterned ground. On intermediate slopes, 2°-6° the forms also are intermediate, being neither true circles and polygons nor true stripes and steps.