Halos Of Stone

In the permafrost regions of the Arctic, soil and rocks are fashioned into strikingly beautiful and orderly patterns that have confronted geologists for centuries. Every summer, the retreating snows unveil a bizarre assortment of rocks arranged in a honeycomb like network as the ground begins to
thaw, giving the landscape the appearance of a tiled floor. These patterns are found in most of the northern lands and alpine regions, where the soil is exposed to moisture and seasonal freezing and thawing. The polygons range in size from a few inches across when composed of small pebbles to several tens of feet when large boulders form protective rings around mounds of soil.
The polygons were probably produced by forces similar to those that cause frost heaving, which pushes rocks up through the soil. This phenomenon is well known to northern farmers, as every spring produces a new crop of stones in their fields. The boulders move through the soil either by a pull from above or by a push from below. If the top of the rock freezes first, it is pulled up by the expanding frozen soil. When the soil thaws, sediment gathers below the rock, which settles at a slightly higher level. The expanding frozen soil lying below could also heave the rock upward. After several freeze thaw cycles, the boulder finally rests on the surface. Rocks also have been known to push through highway pavement, and fence posts have been shoved completely out of the ground by frost heaving.
The regular polygon patterned ground might have been formed by the movement of soil of mixed composition upward toward the center of the mound and downward under the boulders. The material moves down under the gravel in an action similar to that in a subduction zone. The soil might move in convective cells, much as bubbles rise up in a pot of boiling water. The coarser material, composed of gravel and boulders, is gradually shoved radially outward from the central area and subducted along the edges, leaving the finer materials behind. This idea is supported by the fact that the material in the center of the mound often appears churned up. The opposite condition occurs during the formation of stone pits, which are in every respect the inverse of stone polygons. Instead of convection cells circulating up through the center of the polygon and down along the borders, in stone pits the circulation is down through the center and up along the outside. The arctic soil provides an assortment of other geometric designs, including steps, stripes, and nets that lie between the circles and polygons. These forms can reach 150 feet in diameter. Relics of ancient surface patterns shaped during the last ice age measuring up to 500 feet have been found in former permafrost regions. Even images of Mars sent back from spacecraft depict furrowed rings, polygonal fractures, and ground-ice patterns of every description, suggesting that the planets surface water has long since gone underground.
Other examples of patterned ground include polygonal shapes created in desert muds, which were formed by the contraction of the mud when it dried rapidly in the hot Sun. Sorted circles also might form by the increased wearing down of coarse grains in isolated cracks in bedrock. Even vibrations from earthquakes are thought to cause the sorting of some sediments. Pebbles embedded in sand rise toward the surface during ground shaking as a result of convective motions in the sediment. Vibrating sands at the surface congregate into stable patterns, including hexagons, squares, stripes, and circular heaps. Also, curious occurrences of patterns form in sediments on the ocean floor.

Joseph Kieffer
http://jewelryuk.org
from: http://hand-crafted-jewelry.com