Freeze up
As freezing- cumulative upward movement is referred to by in the soil objects by repeated freezing and thawing and frost heave is caused. This is a form of cryoturbation , which occurs particularly in loose and inhomogeneous soils that are susceptible to frost. This effect is best known for the stones that seem to "grow back" in fields, which farmers remove every year in areas with frost . Another effect in this context is that stone slabs or cuboid objects can be placed vertically when they freeze and, as soon as they have reached the surface, stand on the edge with an unnatural appearance.
root cause
The decisive effect for freezing is frost lift . The main reason for this is not, as is often wrongly claimed, the increase in volume of freezing water, but the upward displacement of bottom water, which collects in the form of ice lenses . As with Frosthub, the details of the process are not fully known and are controversial when it comes to freezing. Basically, two hypotheses are distinguished: The frost-pull hypothesis assumes that the top of an object is the first to be caught by the freezing front spreading from above in the ground and thus fixed, whereby it is raised with the upper soil layer as the frost progresses. In contrast, the frost push hypothesis emphasizes the greater thermal conductivity of the object - for example a stone - compared to the ground and assumes that ice lenses therefore tend to form under the stone and lift it. During the thawing process, the object is prevented from falling back into its original position by the early penetration of finer material into the free spaces that are created - this is common to both hypotheses and is reminiscent of the Brazil nut effect . As the process is repeated annually, the smaller movements accumulate and the object can emerge from the ground.
The edge positioning of elongated objects occurs because the part of an object lying further above experiences a greater frost stroke than the part further down, because the freezing front spreads into the ground from above.
literature
- Hugh M. French: The Periglacial Environment. 3rd edition, Wiley-Verlag, Chichester 2007, ISBN 0-470-86588-1
- Albert L. Washburn: Geocryology. Edward Arnold Publishers, London 1979, ISBN 0-7131-6119-1
Web links
- geodz.com: freezing-