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JimboOmega

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Ice Crashing Into Ice
« on: June 22, 2016, 10:03:46 PM »
So there's been a fair amount of discussion - me asking in stupid questions, and people speculating about the current low pressure - about floes colliding.

What do people think happens?

I assume floes tend to  move in the same relative direction - and thus not crash into each other so much.

But what if they get pushed back into landface ice, the pack, etc?  What if underlying wave action causes them to grind on each other where they are already pressed into each other? 

Do they fracture ever smaller? Do they form into a slush? Do they somehow "weld"?

I have no idea, but am opening this thread to speculation, science, and any facts or thoughts people might have.

Okono

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Re: Ice Crashing Into Ice
« Reply #1 on: June 22, 2016, 11:04:32 PM »
My initial hunch was that it shouldn't matter much.  Conservation of energy is universal, and any energy imparted to the ice is going to end up as heat eventually.  Mechanical release of that energy from collisions versus simple drag shouldn't take all that long relative to other timescales.

My second hunch was that my initial hunch is wrong.  There are all kinds of secondary and tertiary influences.  Wind should be able to transfer energy more effectively.  Albedo effects exist.  Momentum is conserved.

But, upon thinking about it, I suspect that we're talking about very little energy compared to everything else, so I would start by running the numbers.  The energy required to melt ice is proportional to the mass, as would be the energy required to move the ice.  Ballparking it, a joule of kinetic energy is good enough to accelerate a kg of spherical cow to 1m/s, but that same kg of ice would require 333,000 joules of energy to melt, no?
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pikaia

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Re: Ice Crashing Into Ice
« Reply #2 on: June 22, 2016, 11:16:09 PM »
Floes don't always move in the same direction.  Depending on the shape above and below water, a floe might be mainly affected by the current, or by the wind. These might be in opposing directions, so that the floes can also move in different directions.

Nick_Naylor

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Re: Ice Crashing Into Ice
« Reply #3 on: June 22, 2016, 11:20:57 PM »
The energy required to melt ice is proportional to the mass, as would be the energy required to move the ice.  Ballparking it, a joule of kinetic energy is good enough to accelerate a kg of spherical cow to 1m/s, but that same kg of ice would require 333,000 joules of energy to melt, no?

It takes a lot more energy to move a block of submerged ice than it would to accelerate the same ice floating freely in space. In addition, the movement of ice on the surface disturbs the water beneath it, potentially liberating heat from deeper water and bringing additional energy into the picture.

So it's not a simple question at all.

JimboOmega

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Re: Ice Crashing Into Ice
« Reply #4 on: June 22, 2016, 11:23:07 PM »
My initial hunch was that it shouldn't matter much.  Conservation of energy is universal, and any energy imparted to the ice is going to end up as heat eventually.  Mechanical release of that energy from collisions versus simple drag shouldn't take all that long relative to other timescales.

My second hunch was that my initial hunch is wrong.  There are all kinds of secondary and tertiary influences.  Wind should be able to transfer energy more effectively.  Albedo effects exist.  Momentum is conserved.

But, upon thinking about it, I suspect that we're talking about very little energy compared to everything else, so I would start by running the numbers.  The energy required to melt ice is proportional to the mass, as would be the energy required to move the ice.  Ballparking it, a joule of kinetic energy is good enough to accelerate a kg of spherical cow to 1m/s, but that same kg of ice would require 333,000 joules of energy to melt, no?

The kinetic energy getting turned into heat is of a lesser concern then, ultimately, the effects on albedo and mixing.

If ice breaks into lots of smaller pieces during a collision, it could cover more area. Of course, water being squeezed and pushed in between pieces could mix up more, bringing (relatively) warmer water up. Smaller pieces have more surface area exposed to warm currents and the like, too. 

There's lots of stuff going on beyond just the heat imparted by the collision.

Okono

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Re: Ice Crashing Into Ice
« Reply #5 on: June 22, 2016, 11:42:01 PM »
So it's not a simple question at all.

I didn't mean to imply that it's simple, which I hope I captured in my second hunch and spherical cow reference.

If I had to place money on the biggest impact, it would be on the increased ice mobility directly leading to or making possible displacement of floes, particularly longitudinally.  That could change overall energy balances, albedo and melt rates, disrupt freshwater lensing, possibly impact circulation patterns and other energy transfer mechanisms, and more.

But, I can't picture any effect of impact or collision, as opposed to export, that would be both persistent and significant enough to matter in the face of many orders of magnitude of difference in energy involved.

My point in emphasizing the numbers is that I would focus on the ice export, and that's already something we watch assiduously.  The very same ratio demonstrates that it takes much less energy to export ice than it does to melt it in place.

So, my wager would be that intra-basin effects aren't likely to be large enough to count in the grand scheme, but I would watch all ice velocities with greater attention.
« Last Edit: June 22, 2016, 11:56:31 PM by Okono »
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crandles

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Re: Ice Crashing Into Ice
« Reply #6 on: June 22, 2016, 11:43:49 PM »
What do people think happens?

Ever heard of ridges?

Archimid

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Re: Ice Crashing Into Ice
« Reply #7 on: June 22, 2016, 11:53:16 PM »
Maybe this lecture has the answers you seek.https://youtu.be/26l2iNw4iJ0?t=37m48s

The whole lecture is great, but the part about icesheest colliding starts about 37 minutes in.
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Sebastian Jones

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Re: Ice Crashing Into Ice
« Reply #8 on: June 23, 2016, 06:49:23 AM »
When there is a storm, the wind causes waves to rise, which can make the ice floes crash into each other. This causes them to break. In addition, different floes have different profiles, which means they catch the wind differently, which means they move at different speeds and even different directions. This also causes collisions. The waves themselves sometimes cause the floes to break. A long lasting storm with plenty of open water can cause mixing of layers of water, some of these layers are warm enough or salty enough to accelerate melting. This can also result in fractures.

DoomInTheUK

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Re: Ice Crashing Into Ice
« Reply #9 on: June 23, 2016, 10:42:03 AM »
The ice collision in itself is not really the issue. The action itself will cause almost no extra melt, and may produce ridges that are more resistant to a melt season. It will depend on how much space is available for the floes to move around in.
Well restrained floes may well end up ridging, less so, and they might just grind some ice off the edges.
The problem really lies in the fact that the ice is broken enough to be mobile. It's far more susceptible to the real melt driver - warm water. Either from warmed water from direct insolation between floes or as melt ponds, or from stirred warmer waters below.
That's why storms over broken ice are far more influential than storms over solid, thick ice.

jdallen

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Re: Ice Crashing Into Ice
« Reply #10 on: June 23, 2016, 05:54:18 PM »
When there is a storm, the wind causes waves to rise, which can make the ice floes crash into each other. This causes them to break. In addition, different floes have different profiles, which means they catch the wind differently, which means they move at different speeds and even different directions. This also causes collisions. The waves themselves sometimes cause the floes to break. A long lasting storm with plenty of open water can cause mixing of layers of water, some of these layers are warm enough or salty enough to accelerate melting. This can also result in fractures.
Actually, its the action of waves and tide which cause most of the small scale fracturing.

I'd suggest people make a visit to this topic:

http://forum.arctic-sea-ice.net/index.php/topic,1222.0.html
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