How are ice bridges formed?

[marty]

Was talking with my friend Sapblatt on Saturday and at one point our riveting conversation turned to the topic of ice bridges.

We began to speculate how they might form over fast moving water, but none of our theories felt right.

Calling all experts: please enlighten us.

Thanks,
Marty

 

[wardsgirl]

I'm no expert, but I've seen my share of ice bridges! I think they form when ice particles freeze to rocks, branches, and debris that stand above the surface of the water. These ice particles are joined by other ice particles and eventually they grow into an ice bridge. That's basically it from a non-scientific point of view.

I can tell you that one day last winter, my BF and I hiked up Mt. Tom. The stream crossing near the notch was dicey. My BF grabbed a nearby birch log and placed it across the stream. We spent the night on Mt. Tom. The next day, the ice had frozen all around the birch log, making the start of a nice ice bridge. When we returned on subsequent trips, over the winter, the bridge had become more dense and sturdy.

Ice bridges: Build one today!

 

[marty]

Thanks for the reply, Wardsgirl. It is probably just as simple as you described. Still very cool!

Regards,
Marty

 

[andrewb]

I have seen this in action as well, I noticed that a crossing of a stream had noticeably more ice a few hours later on the return... and the water was moving fast enough that this seemed counter-intuitive. It may be water spray or possibly humidity rising from the water that attaches to whatever solid surfaces are close enough that bridges the gap.

 

[DougPaul]

It may be water spray or possibly humidity rising from the water that attaches to whatever solid surfaces are close enough that bridges the gap.

When the water is warmer than nearby surfaces, moisture will evaporate from the water and freeze on the surfaces.

Water moves from warm to cold.

Doug

 

[PA Ridgerunner]

It may be water spray or possibly humidity rising from the water that attaches to whatever solid surfaces are close enough that bridges the gap.

I witness this every winter at my home. I have a sump pump which drains outside through a 4" pvc, with a slotted cap (to keep the critters out). The bottom half, where the running water is, stays clear, but ice always wants to build up on the upper half where the water sprays up as it goes through the slots in the cap. So I just keep the outlet cleared of snow and occasionally go out and knock the ice off.

 

[Dr. Dasypodidae]

Happens to the top of my water bottle in winter a lot; can turn upside down some times to keep lid from freezing.

 

[1HappyHiker]

I'm no expert, but I've seen my share of ice bridges! I think they form when ice particles freeze to rocks, branches, and debris that stand above the surface of the water. These ice particles are joined by other ice particles and eventually they grow into an ice bridge. That's basically it from a non-scientific point of view.

I can tell you that one day last winter, my BF and I hiked up Mt. Tom. The stream crossing near the notch was dicey. My BF grabbed a nearby birch log and placed it across the stream. We spent the night on Mt. Tom. The next day, the ice had frozen all around the birch log, making the start of a nice ice bridge. When we returned on subsequent trips, over the winter, the bridge had become more dense and sturdy.

My layman’s explanation about ice bridges pretty much coincides with “wardsgirl”. Ice floats on water, i.e. it doesn’t sink. So my theory is that floating ice collects in the narrow spots between partially submerged boulders, tree trunks, etc. (much the same way as say leaves and other debris collect in these narrow places). So then, this collection of ice forms a clot/clog which slows down the flow of water, which in turn makes the slower moving water more susceptible to freezing. And eventually, this whole process leads to creation of an ice bridge. Dunno . . . maybe my theory is all wet!

 

[wardsgirl]

Even more interesting than how they are formed, is this scary video of one being taken out. I'd hate to have been the videographer. Very scary looking.

http://www.wcax.com/global/video/fl...ageAdTag=Weather&activePane=info&rnd=11885375

 

[PA Ridgerunner]

Even more interesting than how they are formed, is this scary video of one being taken out. I'd hate to have been the videographer. Very scary looking.

http://www.wcax.com/global/video/fl...ageAdTag=Weather&activePane=info&rnd=11885375

dam! er...i mean...damn!

 

[Silverfox]

wow..that is a great video..I sure would not have wanted to be on the wrong side of that brook...

 

[Dr. Dasypodidae]

Incredible video footage; thanks for posting the link! That could have been Shoal Pond Brook on late Friday night, February 27th. Hope to post our Pemi ski-through report soon.

 

[SteveHiker]

look here:
http://en.wikipedia.org/wiki/Frazil_ice

something I learned about while working at the Cold Regions Lab in Hanover back in the early '90s.

The setup they had for experimenting on this was impressive. They had a scale model (1/4th I think it was) of the Ompompanusic River in one of the lab buildings that could be brought down to minus 20 (or maybe lower?)


also there's way more info here:
http://www.crrel.usace.army.mil/techpub/CRREL_Reports/reports/CRTD91_01.pdf