Formation of Patterned Ground
As water freezes, it expands and takes up about 10% more volume. This expansion generates enough force to transform small highway cracks into potholes and to break apart enormous boulders along fractures in the rock through the process known as ice wedging. Pressures associated with ice wedging are known to reach nearly 30,000 lbf/in² (200 MPa), a pressure close to that required to crush granite.
In periglacial areas and areas affected by seasonal frost, repeated freezing and thawing of groundwater forces larger stones toward the surface as smaller soils flow and settle underneath larger stones. At the surface, areas that are rich in larger stones contain much less water than highly porous areas of finer grained sediments. These water saturated areas of finer sediments have a much greater ability to expand and contract as freezing and thawing occur, leading to lateral forces which ultimately pile larger stones into clusters and stripes. Through time, repeated freeze-thaw cycles smooth out irregularities and odd-shaped piles to form the common polygons, circular, and stripes of patterned ground.
Frost also sorts the sediments in the ground. Once the mantle has been weathered, finer particles tend to migrate away from the freezing front, and larger particles migrate through the action of gravity.
Patterned ground forms mostly within the active layer of permafrost. Water percolating through the soil builds up underneath blocks. When it freezes, blocks are pushed up towards the surface. When the soil thaws, the blocks do not return to their original location because finer particles fill in voids. The process may continue until the blocks are completely unearthed.
Read more about this topic: Patterned Ground
Famous quotes containing the words formation of, formation and/or ground:
“I want you to consider this distinction as you go forward in life. Being male is not enough; being a man is a right to be earned and an honor to be cherished. I cannot tell you how to earn that right or deserve that honor. . . but I can tell you that the formation of your manhood must be a conscious act governed by the highest vision of the man you want to be.”
—Kent Nerburn (20th century)
“The moral virtues, then, are produced in us neither by nature nor against nature. Nature, indeed, prepares in us the ground for their reception, but their complete formation is the product of habit.”
—Aristotle (384–322 B.C.)
“The high that proved too high, the heroic for earth too hard,
The passion that left the ground to lose itself in the sky,
Are music sent up to God by the lover and the bard;
Enough that he heard it once; we shall hear it by and by.”
—Robert Browning (1812–1889)