It’s springtime in the Rockies, and, like every spring I get, or overhear, comments to the effect that: “When the weather warms up this fast, it’s gonna really drive the frost deep in the ground.”– Wrong.
But how would you explain that? It’s hard because frost will continue to form deeper in the ground for a time, but not due to warmth from above, just due to the “reservoir” of frozen ground that continues to draw heat from the deeper ground until the whole mass is warmed up from above (and from below, to some extent.)
Is there a good analogy to explain this?
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Well, if the ground warms up and melts some of the frost, the layer of frost is deeper in the ground. This keeps going on until there is no more frost.
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Not to answer a question with a question, but....
How deep was the frost to begin with?
People are people everywhere. I doubt one in a hundred know what the frost penetration ever gets to at any time durring thier winter monts. They just know it is getting warm and the top layer of soil is soft enough to dig. Then they hit a hard layer of frost and make the assumption that the warm weather "pushed" it down.
Surprise, when they get down past the frost layer and the earth temperature is ralatively constant. At least untill you get mega deep like some mines.
The bottom of the frost layer isn't getting deeper but the top of the frost layer is getting father from the surface. (In reality, the bottom is also getting closer to the surface as the natural heat deeper in the earth pushes it up.) So the frost layer is melting from both above and below. The only way to drive the frost layer to a lower point is to have temperatures from above that are well below freezing for a continued period of time.
I think I know what the warning is about...it happens here every Spring when my driveway turns to porridge.
You're correct about the fact that the statement is completely dumb...there's no way that warm weather can "drive the frost deeper".
What happens is that the top 10" to 12" of earth thaw, but beneath that remains a continuous layer of frozen earth that prevent water from above from draining. Until that layer finally thaws you've got vehicles buried up to their axles in muck.
It can be a bit of a nightmare, and it means I've got hours of raking to smooth out my driveway.
I think the reason the ground is so soft is that as the frost thaws, the water expands. It's pushed up through the top few inches of the ground, which turns it into a quicksand-like mess.
Can't prove it, but that's my theory and I'm sticking to it.
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I have driven plenty of gravel roads before and had always hit soft spots in the spring but last year was the first time I ever experience anything so bad with the frost issue on the roads. Was taking my son to boy scout camp and the roads were soft but nut so bad. The I get to the boy scout camp and their is a vehicle stuck up to the axels. Had never stopped and gotten out in these conditions before. The road was literally like walking on a water bed. You could feel the road floating underneath your feet.
They eventually got the guy out and I picked a line, got my speed up and went on through...some times on the road and some off. My two wheel drive suburban didn't have any issue but a lot of the times its the driver that gets the vehicle stuck as much as it is the vehicle.
You can stick to that theory if you want to but you might consider just why is it that your ice cubes happen to float in your water glass rather than sink to the bottom.
Freezing breaks apart the fine particles of the soil, "uncementing" them. Then add in the water layer "floating" on the frost below and you have a receipe for muck.
A little more explanation to my original post:
The thing people notice is that, even after warmer temperatures have arrived, for a time, water lines can freeze that did not freeze before the warmer weather arrived--so they draw the conclusion that the heat "drove" the frost deeper, as if the cold were fleeing from heat.
This is wrong, of course. What is really happening is that the layer under the frozen ground, which may have been near to freezing already, continues to transfer its heat to the layer of frozen ground immediately above. It would have happened regardless of surface warming.
But it gives the appearance that warmth is driving frost deeper. Sort of like trying to explain the sun only appears to rise in the morning--it's really just the rotation of earth that we're seeing.
My question is not about what is actually happening. My question is: what's a simple and clear way to 'splain this to someone who has a hard time grasping what heat transfer is all about?
I lived in Alaska for many years and in the old days mostly we'd hear that expression quite a bit. It came mostly from the "old timers." I would suggest that you explain that cold does not move. Only heat (energy) moves through the ground or anything for that matter. Cold is simply the absence of warmth... both are relative. Freezing is simply a particular temperature of water. If those to whom you are talking to don't accept this, then tell them the frost doesn't want to give up being king-shit of the season and is fleeing from the summer infidel. Furthermore, explain to them that the only way to save their gardens, water lines, driveways, etc it to give you several hundred dollar bills to burn to warm things up a bit.
I don't know where they'd get that idea, and it's thermodynamic nonsense.
I don't know where they'd get that idea, and it's thermodynamic nonsense.
Sure, but it's repeated so often that people accept it. One year, our municipal water supplier sent a flyer along with their monthly bill warning people of the coming spring warmth that "will drive the frost deeper down and possibly freeze water lines, so be sure to leave a trickle of water running in your house to prevent freezing."
Here's another one for ya: my mother used to say that you need to immerse boiled eggs in a pan of cold water to "drive the heat to the center of the egg where it'll cook the yolk." Had to be true--her mother told her the same thing.
Thermodynamics is a mystery
Thermodynamics and heat transfer can be pretty confusing. When I was in engineering school, there were a few kids every semester that couldn't get a C or better in them. This is after they had finished the "wipe out classes", of statics, dynamics, fluid dynamics, three semesters of calculus, and at least two semesters each of physics, and chemistry. So, there weren't any real dummies left, and still confused a few of them. There were even the rare few who could pass one and not the other.
Based on that and things like the conversations I have had with seemingly smart guys who were building their own hot vapor carburetors, or hydrogen generators, to make their 69 Chevy pickup get 80-mpg: I am not surprised that the average guy with little math background would believe that frost gets pushed down in the spring.
I am the average guy with little math background, but what's so hard to understand about this issue? It's not like anybody needs to know specific equations to quantify heat transfer rates by various materials--it's the simplest of all thermodynamic laws: heat always moves from an area of greater concentration to one of lesser concentration.
Maybe there's something intuitive at work here, like the idea that opposites repel, or something. ???