Ice heaves and pressure ridge FAQ.

[_Brad_]

I have searched this site and the Internet for over 2 hours now and I still don't have a firm understanding of ice heaves and pressure ridge. I would appreciate if someone could clarify several things for us all:

1.) What is the difference between both an ice heave and a pressure ridge?

2.) How do you identify both heaves and ridges out on a lake? Where are they most likely to happen? Signs of them forming?

3.) What the heck do they look like?

Any information to better the understanding of heaves and ridges would be valuable and even possibly life saving.

Thoughts?

[Gissert]

Ice heaves and pressures ridges are the same thing.

They happen as a result of changing temps and expansion of the ice. Think of them as being similar to earthquake fault lines. Some areas will have ridges in the same spots nearly every year.

They tend to form on larger lakes, but any lake can have them if the conditions are right.

The seem to be bigger and more frequent when you get below zero temps with little or no snow cover. The lack of insulation allows the ice surface temps to fluctuate with the ambient temp. When this happens, the ice expands and it has to go somewhere. A crack will form, and the ice will push together and form a ridge. It can be a few inches high, or sometimes they can be massive. They are fairly obvious if they are more than a foot high. You will see jagged edges sticking up in a long line across the lake.

Sometimes, one ice sheet wil duck under the other and the pile will not be so high. These are harder to spot, and they will often have quite a bit of standing water on the side that ducks under.

Use caution when crossing ridges - approach them slowly and look for fresh water or wetness. If you determine it is safe to cross, do so at a right angle to the ridge. If it does not look safe, don't hesitate to look elsewhere.

When ice expands, it does not always form a breaker or a ridge - sometimes they will open a large crack that can be a couple inches to a couple feet across. I saw one on LOW one December that was over three feet wide when it formed.

[Minnetonka]

An ice heave and an ice pressure ridge are two different names for the same thing. When ice forms, it expands by 9% and it often will relive the pressure of expansion by buckling or heaving. I have a photo of an ice heave on Winnibigosh that shows one almost 5 feet high. Ice also can be moved by wind and will either push up on shore, or form a heave or ridge. These pressure ridges may form in the same location each year due to factors like points, shallow areas, or the general direction of the wind at the same time each year.

[metrojoe]

It's amazing how much the ice expands and contracts on any given day. We were on Mille Lacs on Saturday and drove across a few cracks that were under pressure from the ice expanding. You could hear it popping and snapping, plus there would be water flowing up from the crack in some spots.

Sometime during the afternoon there was what I could only describe as a mini icequake. I was sitting in my shack at the time, but it could have easily knocked a guy from his feet. It was followed by a loud booming cracking sound.

Later that evening leaving the ice we came across a crack that had pulled apart about 14 to 20 inches. We had to lay the trailer ramps across the open water to get the ATV and trailer across.

I've got a couple of good pics of a ice heave. They are hard copies, but I'll see if the old scanner is working so I can post them later.

[nytelyter]

i seem to recall a post from last year on this very subject that had a link to study done by the dnr or someone. it was a real good read. it covered the whole gambit of how and when it occurs. and how much the ice will move on a given day of temps warming up and recooling. ... paul

[_Brad_]

This is great information ya'all; I really appreciate it! Pictures would be great as all I can really find on google are pictures of ocean pressure ridges and heaves.. Not sure if these are the same as it is salt water..

[fishingman93]

when i used to live in south dakota we had a super cold streak 4 days in a row it was below zero. during that the ice was forming fast and along the shores it heaved up every where and alot of boat houses were ruined. and out in the middle of the lake there where like 6 or 7 ice heaves or ( ice ridges ) they were close to 8 to 9 feet high and the game fish and parks said that from 30 yards out from the heave it was dangerous ice. They were cool but ruined ice fishing that year on that lake cause u couldnt get any where

[_Brad_]

OK, so this brings up another question. How in the hell can the ice be dangerous 30 yards from the heaves when its that cold? Wont the ice just re-freeze within a matter of hours?

[SXViper]

Here is the link from last year.

http://www.dnr.state.mn.us/waters/watermgmt_section/pwpermits/blockbuster.html

Brian

[schweady]

Gotta love a forum that points you in the direction of great stuff like:

"The coefficient of linear expansion of ice, according to Ganot, is 0.000052 per degree of temperature rise, and thus for a 10º F variation in an ice sheet a mile long, the change in length would approximate 2.75 feet while the force exerted is probably not less than 30,000 pounds per square foot."

Thanks, viper!

[Ferny]

Here's a picture link with an ice heave in the background.

Pay no attention to all the Red Lake slab crappies in the foreground. This is a small heave, I didn't take a pic of the larger one they had chopped down and bridged over on the main road. Some of them I have seen on Lake of the Woods and Mille Lacs open up so there is a water filled gap up to 2 feet wide. They usually put metal bridges across them if they are on a resort road. Others have ice piled 6 feet tall along them.

Ferny.

[_Brad_]

Ahhh ha! Excellent photo! This gives me a much better understanding now. Having seen your picture, I now remember seeing something simular before.

Thank you all very much for the information!

[BDR]

rarely are these a clean break in the ice. Many other fractures breaking off, perpendicular, the main heave. Imagine ice cracking off the main heave forming a V, you drive on to the V and it sinks.

It's what I cant see that scares me.

[_Brad_]

I hear ya! Expecially when there is heavy snow cover on the lake.

[BobT]

There's another factor to consider. Ice is less dense than liquid water and so it floats. As the ice forms it develops on the surface and builds down as more and more water freezes. As the ice gets thicker its bouyancy begins to cause a pressure to build from the bottom up. Eventually a fracture may form and the ice sheet suddenly lunges upward. When this happens, the two ice sheets now have room to spread apart creating an area of open water. These can be even wider than 3' as was earlier described. I have referred to this incident a few times before but I remember one year on LOTW when a 6' wide fracture opened and then a thin layer of ice formed on the newly open water. About the same time, it was snowing and the entire fracture was hidden because there was no noticable heave. A bombardier from a local resort drove right into the fracture killing everyone inside except the driver who managed to make it out. That's one reason ice can be unpredictable even in late January. This incident happened about two weeks before we were scheduled to arrive for a fishing trip in mid-February. The ice on the lake was nearly 4' thick in most areas.

Bob

[_Brad_]

That is unreal! All this is more the reason to drive slow and I guess get ready to jump out!

[DEADhead]

Thanks for the reality check Bob! I know I can get into a state of complacency once the first foot or two of ice forms. A lot of the smaller lakes around here don't always get those big problems with heaves, so you tend to forget that they happen. Your post is really a good reminder on ice safety.