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This question is not a duplicate of either (1) Ice skating on a frozen lake -- how thick should the ice be?, which only asks how thick the ice should be; or (2) How to determine the thickness of ice?, which only asks how to determine how thick the ice is.

When I was a child, we skated on a couple of lakes in Connecticut. One day my father would declare that "It's safe now" and off we would go. No one ever fell through. He did not drill.

My question is: short of drilling, how do locals decide the ice on their lakes is safe for winter sports? I don't remember the criteria my father used, except on the larger lake the ice had to extend very close to the spill-way, which was in essence an artificial outlet stream. (We stayed away from that area.) If it was safe on the larger lake, it would be safe on the smaller lake.

Where I live (Northern VA), the only safe assumption is that the ice is never safe.

Clarification: If you think drilling is the only way to declare ice safe, in your area for your lakes, that would be a valid answer. But I am still more interested in how people can make the judgement without drilling.

  • I know that in some places there's a system like a week with -6C or lower every night and never above freezing. Whether they then double check by drilling is another matter. – Chris H May 2 '16 at 7:31
  • I'm pretty sure I've already answered this question... – ShemSeger May 2 '16 at 20:11
  • @ShemSeger Only the two previous questions I mentioned in my Q showed up in the "search", and you did not answer either. If you have given another answer somewhere, I'd like to see it. You are right about the edges. – ab2 ReinstateMonicaNow May 3 '16 at 1:37
  • @ab2 I noticed, perhaps I only thought about answering... – ShemSeger May 3 '16 at 20:40
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    Easy - the locals send visitors out and see if they fall through! – Jon Custer Mar 22 at 16:14
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You need between 3 and 4" of clear ice to be safe, but, with practice, you can visually determine if there is this amount or more. The key is that ice can support your weight in boots and not yet be safe for dynamic or concentrated loads (i.e. jumping or ice skating).

The basic technique is that you first bash the edge of the ice (it is always thinnest at the edge), and look at the thickness underwater. If your bashing put a lot of cracks in the ice or the ice moved on the water, it isn't safe enough to step on.

Then you step on the ice -- if it cracks and seems springy, you jump off.

Then you jump up and down -- if that's ok, you go out a few feet and look at the ice at slanted angle.

Because clear ice refracts light differently depending on its thickness, with a little bit of practice, you can see if the ice is 4"+ thick. In general, if it is 2" or less, a well-driven ski pole will go through it, and if you jump, it it will crack and water will come up through the cracks.

Overall, this is something of an experience-based process.

  • 1
    Most people who know ice can tell just by looking at it if it's going to hold their weight. – ShemSeger May 2 '16 at 20:19
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    The question was "how do you know"... I know what good ice looks like, but I was trying to figure out how to explain that to someone else. – gbronner May 2 '16 at 20:22
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My question is: short of drilling, how do locals decide the ice on their lakes is safe for winter sports?

What people in North America do (for testing if you can walk on the ice) is:

  1. Check that the edge is thick enough to hold your weight, if you can't get on the edge you won't get to the middle (without getting soaked, which is the #2 thing to avoid).

  2. Slowly walk a little further, if you can feel flexing or hear cracking slowly turn around.

  3. Venture out further and look to see if the ice appears consistent, if it doesn't seem fairly thick and free of cracking and flexing then wait another day or two while temperatures remain a few degrees below freezing. If it gets warmer it's best to forget about going out on the ice.

  4. You can find a shallow depressed area and fill it with water, that way if the ice is uncertain you won't fall in past ankle depth. Such an area is much safer for playing sports with many active people than the risk of letting your children play on a frozen lake.

An additional test that I utilized, since I didn't enjoy getting a soaker in freezing cold water, is to lob a large rock onto the ice. You can tell from the bonk (and above listed checks) that the ice looks and sounds correct.

On the Internet these seemingly reliable sites offer this advice (not involving drilling):

  • Outdoor Canada Magazine: "How to know when the ice is safe for fishing":

    "Freeze Factors

    ... the first question you should ask yourself at the beginning or the end of the season is this: Has it been cold enough outside for a long enough period of time to create or maintain safe ice? If the answer’s no, it’s not time to go ice fishing.

    When you do visit a frozen waterbody, conduct a visual inspection before heading out. Look for cracks on the surface, which can be a sign of instability. ...

    Colour code

    It’s also very important to consider the colour of the ice. Clear blue ice is the strongest and safest. It forms when the temperature has been at least -8ºC for three consecutive weeks. The colder it gets, the faster blue ice will form. At a minimum thickness of 12 inches, blue ice will even support a large vehicle such as a mid-size pick-up (see “Support system”).

    White opaque ice is half as strong as blue ice. It’s formed by wet snow freezing on top of already existing ice. Often referred to as snow ice, it’s most dangerous when it forms on top of ice that hasn’t completely frozen. When that happens, the ice below takes longer to freeze and turn into blue ice. During early-winter and spring snowstorms, opaque ice is notorious for covering up dangerous thin ice, catching ice anglers off guard. Use extreme caution when heading onto snow-covered ice, and check the thickness every 100 metres with your ice auger.

    Dull grey ice is the least safe. Why? Because it’s rotting. The grey colouration indicates the presence of water, meaning the ice will not support much weight, if any. Grey ice is most common during the spring melt, although it can be found all winter long near moving water, such as where creeks and rivers enter or leave a waterbody. These same areas also often have underwater currents that can make ice unstable, so avoid them. And remember, no fish is worth the risk of falling through.".

  • WikiHow: "How to Know When Ice is Safe" (read complete article for details):

    1. Recognize that ice will never be completely safe.

    2. Create an emergency safety plan.

    3. Recognize that determining the safety of ice is dependent on a combination of factors, not on one factor alone.

    Ice safety is determined by assessing the following factors together:

    • Appearance of the ice - its color, texture and features

    • Thickness of the ice - there are recommended thicknesses for different uses, which are set out below

    • External temperature over a period of time and on the day

    • Snow coverage

    • Depth of water under ice

    • Size of water body

    • Chemical composition of water - whether water is fresh or salt

    • Local climate fluctuations

    • Extent of ice

    1. Prefer ice that is checked by designated authorities on a regular basis.

    2. Ask the locals.

    3. Observe the ice. Look at the ice to see if you can see any cracks, breaks, weak spots or abnormal surfaces and to identify the color(s) of the ice. You cannot rely on your eyesight alone. This is just an initial look to help you to decide if it is even worth proceeding to the next step of testing the ice.

    If you see any of these signs, you may wish to abandon any further attempt to go on the ice:

    • Flowing water near or at the edges of the ice

    • Flowing springs under the ice in spring fed ponds and lakes

    • Water flows in and/or out of the iced-over water body

    • Cracks, breaks or holes

    • Ice that appears to have thawed and refrozen

    • Abnormal surfaces that you have not seen before - e.g., pressure ridges caused by currents or winds

    Remember this ditty: "Thick and blue, tried and true; Thin and crispy, way too risky."

    1. Know your ice color meanings. Although a useful indicator, color alone should not be relied upon. For instance, ice of any color subjected to a running water force underneath will be weaker than ice not subject to that pressure. In general, you can surmise the following from ice colors:

      • Light gray to dark black - Melting ice, occurs even if air temperature is below 32°F (0°C). Not safe, its weak density can’t hold a load, stay off.

      • White to Opaque - Water-saturated snow freezes on top of ice forming another thin ice layer. Most times it’s weak due to being porous from air pockets.

      • Blue to Clear - High density, very strong, safest ice to be on if thick enough, stay off if less than 4 inches (10 cm) thick.

      • Mottled and slushy or "rotten" ice - not so much its color but its texture. This ice is thawing and slushy. It is deceptive - it may seem thick at the top but it is rotting away at the center and base. Most prevalent in spring, may be showing signs of browns from plant tannins, dirt and other natural materials that are resurfacing from thawing. Not suitable for even a footstep.

    2. Test the thickness of the ice. If you have already made your observations and you still feel confident, you will need to back this up by checking the thickness of the ice.

      • Test with at least one other person (the buddy system). Wear a flotation suit or device and use ropes that your buddy can pull on if something goes wrong.

      • Only go on the ice if the edge of the water body is firm. If it is slushy or cracking, it is unlikely to be safe to proceed as shoreline ice is the weakest.

      • Etc. ...

    3. Understand that ice strength is not the same everywhere, not even on the same body of water.

    4. Find alternatives if in any doubt. Skaters can always find a rink or a supervised lake area; snowmobilers and skiers can always stick to trails on land in place of crossing ice; walkers can keep off the ice and continue with their snowshoes along the trail. All out-goers should carry emergency supplies no matter how long they plan to be out nor where they plan to go.

Those are lengthy articles that are grossly abbreviated for this answer.

  • Canadian Red Cross: "Ice Safety"

  • Boy Scouts of America: "Ice Safety"

  • My answer on Physics.SE to "When can water be supercooled" which contains charts regarding pressure and freezing temperature along with a link, huge chart of ice types, leading to a website containing more information about ice and water than the average person would want to know.

Proper drilling would involve drilling and measuring at sufficiently frequent intervals to chart the thickness safely, due to the uncertainty of ice it would provide a time consuming guess.

A great method not involving drilling is explained in this article: "Non-contact ice thickness indicator ‘PicoR ICE’ powered by XeThru radar tech". The PicoR Ice Device is one of many such devices for rapidly measuring ice fields.

Ice Radar

I suspect that most people, your father included, simply guess that the ice is safe; with varying results.

See also Psychology.SE:

The last link explains that paying to go to a skating rink is cheaper than losing your life, but people think waiting until they decide it is safe to skate (or drive a vehicle) on a frozen lake is the lowest cost alternative.

8

In sweden, where skate touring is a popular winter sport, skaters bring a device called "ispik". (Ice pike). They come in two varieties. Either double pike, that looks like a sturdier version of a ski pole or a single pike that looks more like a broomstick with a tapered metal point. Generally speaking a single pike is easier to use but a double pike can also be used in the same manner as a cross country skier uses poles, which is useful if the ice surface is uneven and hard to skate.

Skaters judge the thickness and quality of the ice by one or more stabs with the pike. With a bit of practice it is quite easy to tell safe ice from questionable ice. Experienced skaters can also tell "thin but it will hold" from "time to turn around".

While skating, the sound is also a useful clue. As the ice gets thinner, the pitch will rise.

6

A quick online search shares a few tips which echo what I've heard from ice fishermen and experienced myself:

  • Ice freezes first and thaws first at the edges, and these areas tend to be weaker. Knowing the terrain and where the shallows and weak spots are is important.
  • Larger and more turbulent bodies of water take longer to freeze.
  • If you're going to test the ice, use sticks and rocks to simulate concentrated weight and impacts - not yourself.

There are some visual cues you can look for - the color of the ice, signs of cracking or slush (or lack-thereof):

Clear, blue or green ice might be thick enough to skate on. White ice typ­i­cally has air or snow trapped inside, weak­en­ing it. Dark ice might be an indi­ca­tion that the ice is quite thin—probably too thin for skating.[1]

In this case I think local knowledge, or Traditional Ecological Knowledge, gained over time through the science of experience, is very valuable in your search. Your father had a way which worked to tell if the ice is safe, where did he learn that from? Do others in your area have similar methods which could be passed unto you?

For example, it sounds like using a weak point on a larger lake as a reference could indicate if the smaller lakes are safe. That could be sensible if the reference point was an over-cautious indicator of the conditions needed for the smaller lakes to be safe. Others may use other indicators - X amount of days below 0 degrees, some combination of temperature and precipitation, etc. but it depends on the location and environmental features. Thus, I'd say your best bet is to refer to local knowledge on what indicators are reliable for your area.


[1] http://blog.theclymb.com/tips/8-safety-tips-for-playing-on-frozen-lakes/

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    "The ice is always thicker at the edges than in the center. If the edges seem safe, you're not done testing yet." Not in my experience it isn't. The shore has rocks and reeds and all sorts of other things which catch the sunlight and radiate heat into the ice, making it thinner and brittle. If you can see the ground through the ice, then there's going to be warmer water under it. Out in the middle, the ice grows thicker over the cold dark depths. Also, ice always melts away from the shore first. I've never fallen through out in the middle of anything, but broke through near shore a lot. – ShemSeger May 2 '16 at 20:16
  • @ShemSeger looking online I see conflicting info on this. In my experience the ice forms in the shallows first and also melts there first, and I think I agree that the edges tend to be thinner. So I've edited the first quote to base it on my own experience and emphasize further the importance of knowing the local terrain for the weak spots, indicators, etc. – cr0 May 3 '16 at 12:25
  • You are right, when ice is first forming it can be thicker at the edges as it freezes towards the centre. But long frozen ice, or melting ice is thicker towards the middle. – ShemSeger May 3 '16 at 20:44
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Aside from all the technical thickness and keeping the "no safe ice" in mind, here is a little "traditional method". I grew up in northern China and now live in Canada. When I am in doubt of ice thickness, I would find a rock, 20-30 lb (not so rounded ones), with edge and toss it far and high. This usually punch through 2 inch of clear ice which is the minimal to support an adult. This also reveal potential crack and hole melted by underwater spring.

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