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Author Topic: Snow.. How come it melts when on pavement??  (Read 7249 times)

Offline Seany

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Snow.. How come it melts when on pavement??
« on: 06/04/2008 09:49:11 »
I woke up this morning to find 15cm thick snow everywhere.. On the fields, gardens.. cars!!

But it seemed that the only place there wasn't snow piled up was where there was pavement!! Why was this?


 

Offline rosalind dna

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Snow.. How come it melts when on pavement??
« Reply #1 on: 06/04/2008 11:16:15 »
Seany I know what you mean about the falling snow and it's deep here also I think but I am not too sure about the reason for the snow melting on the pavements, it could be something as simple as
people walking on it.

Then I am in London and the roads are snow-free for now. I am going out later.
 

Offline Seany

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Snow.. How come it melts when on pavement??
« Reply #2 on: 06/04/2008 11:28:18 »
Well the roads.. They put salt and grit it!! So there isn't snow there..

But the on the pavements in my back garden!! There is a clean trail, just where the snow has melted, and it's just on the pavings..

I think it's the heat from the Earth coming up, that melts it? But on the grass, the snow is far away from the ground, as it isn't exactly touching.. That's my theory!!
 

Offline Carol-A

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Snow.. How come it melts when on pavement??
« Reply #3 on: 06/04/2008 11:48:57 »
It's just that the stones hold more heat, have a greater thermal capacity. If it had been really cold when it snowed, the stones in your garden would get staying snow first. The roads hold the heat from all the cars driving on them.. that's why small side roads get snow build up more quickly, even in the middle of the night when there's little traffic anywhere.
 

Offline Seany

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Snow.. How come it melts when on pavement??
« Reply #4 on: 06/04/2008 11:49:56 »
Tank yoo Carol!! :)
 

Offline Seany

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Snow.. How come it melts when on pavement??
« Reply #5 on: 06/04/2008 11:50:32 »
Wait.. So the stones take ages to gain heat, but also takes ages to lose heat?
So if the stone was cold, then it would take ages to get it heated
And if the stone was hot, it will take a while for it to cool?
 

Offline rosalind dna

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Snow.. How come it melts when on pavement??
« Reply #6 on: 06/04/2008 11:59:54 »
My local council hardly ever bothers to put grit or salt down.
They didn't do that today. The reason is the car's exhausts
are some of the reason but it'll be icy in the morning.

Because stone is a different type of substance than earth into which the snow melts through quite easily. At least that's my experience.
 

Offline Seany

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Snow.. How come it melts when on pavement??
« Reply #7 on: 06/04/2008 12:22:46 »
Thank you!!
 

Offline graham.d

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Snow.. How come it melts when on pavement??
« Reply #8 on: 06/04/2008 13:02:08 »
Carol-A is right I think. Snow will melt if in contact with a reasonably thermally conductive solid at a temperature more than 0 deg C. The air and ground temperature are higher than that in most of the UK at the moment, so the snow melts on contact. It does not melt on grass because the blades of grass suspend the snow above the ground and effectively insulate it. The conductivity of the air is low so takes a long time to melt it. The same is true of the snow suspended on tree branches.
 

Offline Seany

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Snow.. How come it melts when on pavement??
« Reply #9 on: 06/04/2008 13:04:05 »
But if the snow was fast on coming down.. Then the snow would settle on top of the snow that settled on the rock??

But maybe the snow came down gently...
I was not awake to see it snow!! We just woke up at 9am and it was covered
 

Offline graham.d

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Snow.. How come it melts when on pavement??
« Reply #10 on: 06/04/2008 16:20:04 »
Yes, you are right. And this can give the snow a longer life. But once the lower layer melts to form water it tends to also aid the heat conduction which also then helps to melt the snow. It all depends on the relative temperatures.
 

Offline Make it Lady

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Snow.. How come it melts when on pavement??
« Reply #11 on: 06/04/2008 16:48:43 »
I thought it was also to do with colour. Maybe it is because they is black. I'm talking radiation here. Heat rises from dark areas of ground such as ploughed fields, carparks and roads. This is how gliders work. They rise by circling over the thermals caused by rising heat from these areas. They then glide to the next thermal.
So heat absorbed by dark areas during sunny periods is given out again melting the snow.
Busy roads don't collect snow because of friction heat from cars running over the surface. 
 

Offline graham.d

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Snow.. How come it melts when on pavement??
« Reply #12 on: 06/04/2008 17:06:27 »
Hmm, may have an effect on the initial temperature, but my path is made of light coloured bricks with the same result. I suspect the colour could have an effect in certain circumstances though.
 

lyner

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Snow.. How come it melts when on pavement??
« Reply #13 on: 06/04/2008 18:24:02 »
It's just that the stones hold more heat, have a greater thermal capacity. If it had been really cold when it snowed, the stones in your garden would get staying snow first. The roads hold the heat from all the cars driving on them.. that's why small side roads get snow build up more quickly, even in the middle of the night when there's little traffic anywhere.
The energy supplied from passing cars is minimal but they compact the snow and make it a much poorer insulator- it can get heat from above and below and melt quicker when it is squashed. Also there is the effect on the reflectivity. Dirty snow will absorb more radiant energy from the Sun  than clean, white stuff. (This has repercussions on the state of the Poles - not the plumbers, you understand)
I wonder about actual heat capacity being relevant to this - or even which surface has greater specific heat capacity - I think, again, it is more to do with conductivity / emissivity. And, of course, on gardens and rock surfaces, the melt water will run away and leave an insulating gap under the snow whereas, on roads, it stays there and can act as a thermal path between road and snow.
Many factors at work here, I think.
 

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Snow.. How come it melts when on pavement??
« Reply #13 on: 06/04/2008 18:24:02 »

 

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