Have you ever wondered about the piles of rocks you see in the corner of a farmer’s field? Every spring, when farmers plow their fields, they find large rocks that weren’t there the previous year. Does the boulder fairy make deliveries? Nope. The truth is, the rocks have always been there, hiding deep in the soil.
Thanks to the process of frost heaving, every spring sees the surface emergence of new rocks, stones and boulders.
Frost heave is the by-product of the freezing and thawing process of water, particularly of water in soil. The cycle of freezing and thawing in the soil and the formation of seasonal ice deep in the ground create an upward movement of objects in the soil. The freezing and thawing essentially squeeze the soil, causing solid objects like rocks and boulders to heave upward toward the surface.
Frost heaving requires that three factors be present: freezing temperatures, a continual supply of water below, and a particular type of soil.
Although it may be easy to say that frost heaving is simply the result of the expansion of frozen water, other factors are involved that increase the upward thrust. The formation of ice lenses in the soil is the driving force of frost heave.
Ice lenses are large, thin sheets of ice that form in frozen soil, either at or just behind the freezing front. They can range in thickness from paper thin to metres in thickness. Ice lenses grow parallel to the surface of the soil. The ice lens, because it sits at the edge of the freeze line, is fed by warmer water in the soil below it.
The presence of frost susceptible soil with a porus structure allowing capillary flow is essential to supplying the water to the ice lenses as they form. Frost heave is more evident in soil that more easily lends itself to capillary action. This type of soil tends to be finely textured with a balance of loams, silt and sand that is permeable. Glacial soil deposits most often have the right combination and texture of soil to be conducive to capillary action and therefore frost heave.
When the soil freezes and thaws, multiple ice lenses can form, stacked on top of each other with a thin layer of frozen soil between them. During frost heave, one or more soil free ice lenses grow, and their growth displaces the soil above them.
The surface emergence of rocks and boulders in fields is the end result of a complex behavior of water within porous, glacial soil. As the water is pulled upward by the formation of ice lenses, it brings with it solid material like rocks, that are forced to the surface by the cycle of freezing and thawing.
To log this eartchache message the CO the answers to the following questions:
- Why do you suppose the land owner has stacked these rocks in the corner of the field?
- What is the appoximate height of the pile of rocks on the west side of the road?
- What is the approximate length of the pile of rocks (east west direction) on the east side of the road?
- What size are the largest rocks in the pile?
- What three elements are required for frost heaves? Do you see any evidence of any of the elements?
- Optional but fun - post a picture of yourself or gps near gz