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Brad
02-04-2007, 08:29 AM
Okay, this is weather related. In the spring on gravel roads it is common to see large rocks start to show up in the road. The prior fall they were not there. As the spring progresses the rocks stick up higher and higher till they need to be dug out.

Question - why does this happen?

Brad
02-04-2007, 08:33 AM
I have a theory. Yes, it is just a theory - but let me explain my logic.

- In the fall the ground has a lot of moisture
- then it all freezes - above, all around and under large rocks in the ground.
- In the spring the ground above the rock thaws (turns to mud in most cases) then the ground around the rock thaws.
- The ground under the rock is still frozen. Water expands when it freezes so the rock is being held "up" by the ice in the ground below the rock.
- the ground around the rock settles as the ground thaws leaving the rock to appear to rise up (grow).
- after a few years of this the rock works its way closer to the surface and eventually starts to appear in the road above the surface.

Does this make sense or is there another real answer?

Gorque
02-04-2007, 10:39 AM
The rock fairy? :D

Brad
02-04-2007, 12:39 PM
The rock fairy? :D
Has to be a very strong rock fairy.

So, we have 2 answers to the question now.

Charlie
02-04-2007, 02:05 PM
your theory is wright

i see rocks in my back yard after winter that were not there i the fall

Steve M
02-04-2007, 08:02 PM
I believe you are right on target, Brad. Because the ground thaws above and around the rock first, the pressure from below which was caused by the expansion of the water freezing, actually pushes the rock toward the surface as the prussure from above is relieved. But, since the ground freezes from the surface down, why doesn't the rock get forced down in the fall?

Brad
02-04-2007, 08:18 PM
I believe you are right on target, Brad. Because the ground thaws above and around the rock first, the pressure from below which was caused by the expansion of the water freezing, actually pushes the rock toward the surface as the prussure from above is relieved. But, since the ground freezes from the surface down, why doesn't the rock get forced down in the fall?
The rock can not go down in the spring since the ground under it is still frozen. The rock protects the ground under it so that will thaw last.

As the ground under the rock starts to thaw the rock is being held up - and my guess is that some of the thawed ground will flow in from the sides to fill the gaps.

Steve M
02-04-2007, 08:34 PM
O.K., I'm not saying the rock would go down in the spring, on the contrary, it would rise in the Spring. Because the pressure under the rock is still pushing up, while the ground is thawed above, it allows the rock to rise.

Steve M
02-04-2007, 08:46 PM
I see what you are saying about the ground sinking in around the rock because of the space created by the still frozen ground under the rock and the thawed "mud" around the rock...Good point!

Bill O
02-04-2007, 09:12 PM
This doesn't just happen on gravel roads, it happens everywhere. New England field are a good example. Rocks are always working there way up to the surface, its the result of heaving and thawing. Every spring New England farmers spend a significant amount of time just picking rocks and moving them to the edge of the field. Rocks that weren't there last summer.

KD Talbot
02-05-2007, 08:52 AM
I don't think the rocks are actually being pushed up. I think the saturated ground surrounding them is warming and drying out and therefore contracting and revealing them. Not sure if I'm correct, but food for thought.
KDT

Patrad Fischroy
02-05-2007, 09:53 AM
No, the rocks are being pushed up. I too grew up in the New England area and long noticed this, usually as my father and I were trying to get the garden ready for planting. It also is much more pronounced when the soil is silty, that is when the particle size is larger than clay yet smaller than sand. I do recall from my geology and soil science classes in New Hampshire seeing some graphs that showed soil pressures as a function of particle size. They also spoke about how lenses of moisature would form in the shadow beneath a rock. The only thing that I did not understand then, nor do I now is how a rock would move from a point below the frost line (36-48" in most of New England) up to a point where this effect could take place.

Disclosure: Unlike my comments on weather where I have only a passing knowledge of the subject, I did completes a BS and an MS in geology. Whether that means I have competency is another thing entirely, but I am pretty well read in that.

Yankee
02-05-2007, 06:22 PM
This doesn't just happen on gravel roads, it happens everywhere. New England field are a good example. Rocks are always working there way up to the surface, its the result of heaving and thawing. Every spring New England farmers spend a significant amount of time just picking rocks and moving them to the edge of the field. Rocks that weren't there last summer.


Well said Bill. We called them "frost throw ups". I spent many a spring helping to clear the neighboring farmer's fields in my younger days. For 8 hours of hard labor I earned the then whopping sum of $5.00 and was fed lunch!