When will frozen lakes kill me?
February 15, 2007 10:19 PM   Subscribe

Under what conditions are frozen lakes safe to be on? Is any noise coming from a lake bad or just earth shattering cracks nearby? Sorry of this seems silly

I live in Bloomington, Indiana. I have had several occasions to walk around on frozen lakes, but not often enough to have what I would call "experience" doing so and I've never heard or been given any particular instructions in terms of safety precautions.

How thick is thick enough? Is there a way to easily ascertain thickness by sight or sound (and not cutting)? What about when it's snow covered? Deep rumbling seems like an okay thing, but when do you know it's not?

One of our lakes (Griffy) has been frozen for at least a week, during which I've gone walking around on it several times. Just yesterday I went walking on it in the middle of the day while many others were walking around and some people were ice fishing. Tonight, when it's even colder, I went back out with some friends and you could distinctly hear what sounded like distant rumblings. At one point there was a distinct, nearby, cracking noise that prompted our leaving.

From a logical standpoint it seems like a frozen mass that large would be constantly slightly shifting, and thus cracking, but when does this spell certain death and when is it just "normal" and not to be worried about. Or should it always be worried about?
posted by ztdavis to Science & Nature (11 answers total) 1 user marked this as a favorite
The U.S. Army's Engineer Research and Development Center has just the thing.
posted by rolypolyman at 10:31 PM on February 15, 2007

Also, check out this US Army guide to ice thickness. I'd suggest asking the ice fishers how thick the ice is.

Cracking sounds are perfectly normal, even when the ice is a couple feet thick. Lakes do freeze up faster than rivers, but still, I'd never dream of walking on a lake that had only been frozen for a week.
posted by teg at 12:31 AM on February 16, 2007

While it's probably much better to be safe than sorry, all the U.S. Army stuff is a lot more than my family has ever done before going ice skating in New England.

A week of sub-freezing temperatures should be fine for walking and skating, as long as you're cautious.

You can usually get a pretty good idea of how thick the ice is by looking at how deep the cracks in the ice look. Ideally they should look about six inches or deeper, though we've skated on as little as three inches. I don't think I've ever been around any ice much more than a foot deep, and I've done a lot of pond skating. Rumbling and cracking are very normal (though it shouldn't be cracking constantly.)

Be aware that the thickness of the ice can vary a great deal over one body of water - definitely be careful near any part of the lake where a current might be running (near a waterfall, stream outlet, etc.) Also be aware that snow can make ice weaker - fresh, un-snowed-on ice is the safest.

It might be a good idea to learn some basic ice safety and rescue techniques, too.

Enjoy your frozen lakes! I'm stuck in Chicago near nothing but Lake Michigan, far away from all the pretty little New England ponds. Alas.
posted by bubukaba at 12:57 AM on February 16, 2007

I've driven on a few frozen lakes in northern WI during ice fishing season. There will always be cracking but if the ice is thick enough you are in no danger. The quickest way to check is to measure the thickness through one of those ice holes. For walking 4 inches of clear ice should be enough to prevent you from falling through. For driving, 8-12 inches is good.
posted by JJ86 at 5:59 AM on February 16, 2007

And even well-frozen lakes (i.e. 12" or more) can make loud groaning popping noises, especially when it's windy. (I'm a MN native)
posted by craven_morhead at 6:02 AM on February 16, 2007

Not an answer to the question, but anyone interested in the topic should by all means watch the first film in Krzysztof KieĊ›lowski's Dekalog series. It's one of the most stunning things I've ever seen in a movie theater.
posted by languagehat at 6:05 AM on February 16, 2007

I was always told as a kid that there was a difference between cloudy ice and clear ice, or dark ice and light ice, or something... anyone remember what it was, and if there's any truth to it?
posted by sonofslim at 7:53 AM on February 16, 2007

Dark ice is the most solid. Cloudy ice has a good mixture of air in it and is probably not as safe.
posted by JJ86 at 7:55 AM on February 16, 2007

I'll second/third the noisy frozen lake comments....my parents live across from a lake in New England, and when it's cold and windy, it can get pretty loud....cracking, popping, deep splashy sounds, groaning. It's a pretty cool spectacle.

As far as what's safe, there's a few things you can do....contact your local fire dept - in my parent's town, they check several times a day and collect regular reports from residents who live on the shores. Check with the fishermen to see how much ice they had to drill through. Or just look around...if there's a lot of locals out there, you're probably alright. Similarly, if everyone seems to be avoiding a section, you'd probably serve yourself well to do the same.
posted by nevercalm at 9:52 AM on February 16, 2007

My stepfather drives across a river to get to work in the winter (on the east coast of Canada.) I know they wait until there's a foot of ice, but there's also some thing about when the full and new moons are... the ice cracks a certain way? It sounds like looney toons but in that area they've been doing this as long as there've been cars so I guess they know something.
posted by loiseau at 2:48 PM on February 16, 2007

Is there a way to easily ascertain thickness by sight or sound (and not cutting)?

I can say with a fair degree of confidence that nothing as yet exists which can do this reliably. At work, we've sponsored the development of sonar and ground-penetrating radar devices to do exactly this. Sonar can do this but must be in direct contact with clean ice, so is not very useful (it's no quicker than an ice auger really). GPR has a lot of potential, particularly as it can be mounted on an aircraft which allows for covering big areas...

...BUT: What about when it's snow covered?
That's the big problem with any sensing system to date, and why these systems haven't made it out of the lab even with 25 years+ of research. Snow is a great absorber of sound and radar. Even a small amount of snow cover, and worse varying snowcover, masks the ice enough to make thickness determinations very difficult.

Radar (centimetre-band SAR especially) is very useful for tracking free ice movement (and Canada has a federal agency devoted to doing just that), but they can't do thickness measurements with their systems.
posted by bonehead at 6:05 AM on February 17, 2007

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