Lake Ice - Skating Hazards

An Overview of some of the hazards associated with wild ice skating

Summary:

Stay off the ice or prepare to go through

-Advice from Dr Gordon Giesbrecht from his paper Thin Ice

Detail:

Nature of the risk

The risk profile of wild ice skating is similar to moderate mountaineering or back country skiing in terms the need for proper equipment as well as the knowledge and the skills needed to stay out of trouble or to recover when you get things wrong.
It takes a while to develop a reasonable level of situational awareness. Study and prudent curiosity help the process.
Most people who spend enough time on the ice fall through or get banged up in a fall. Having the right safety equipment and having practiced getting back on the ice in controlled conditions (belay, etc) makes a big difference in how things go when/if you fall through unexpectedly.
In Sweden, with their large wild ice skating population, breakthroughs are expected and well prepared for. Their system of skating clubs and deep understanding of the risks assures that most skaters take the most important precautions and developes the key skills. Getting wet is generally accepted as part of the game.

Risk Numbers

For most recreational sports, risk is poorly understood, often because the size of the participating population is not known. Skating is an exception. Skridskonätet (Skater Net) keeps track of accidents within their affiliated clubs so we have good insight into the ground truth.
Based on 100,000 skater trips over the past 4 years in (mostly in Sweden, Finland, Norway and the Netherlands), the average rate of skaters falling through is about once in 170 outings. The injury rate is 74% of that and serious injuries (broken bones, etc) account for 16% of all injuries.
Looked at another way, for a skater who makes 10 ice trips a year the average time between swims is 17 years. For injuries it is 23 years and for serious injuries: 150 years. Having said that, the Swedes are significantly more methodical about safety than we are in North America.
Your specific level of risk has a lot do with how you approach ice. If you are well equiped, methodical and prudent, you should be able to match the average Swedish levels of risk.
The Skridskonätet annual accident reports have a summary in English which offers additional valuable insight.

Ice Unifromity (and the lack thereof)

Thickness recommendations (for cold ice without other issues). The Minnesota DNR recommendations are a reasonably conservative. More on ice thickness

A lot of breakthroughs occur when there is thinner/weaker ice mixed with a much larger amount of thicker ice.
Thinner/open spots can be holes of various types, newer ice, pressure ridges, leads, etc.
New ice is more likely to have areas that froze later and are thinner. Use your test pole to identify and avoid them.
A great looking piece of ice

Ice Noise: Ice makes a wide range of noises. If the ice is thick (4+" for people on foot) and cold, almost all of the noise is related to cracks forming when the ice sheet is warming or cooling. This presents little risk. Occasionally a ridge shifts or comes in with a loud bang. Unless you happen to be standing on the ridge at the time (which is very unlikely) this also presents little risk. On ice thinner than about 3" there is often some relatively quiet cracking noise associated with your weight on the ice. This is a signal to you that you should verify that the ice is as thick as you think it is with your test pole or by looking at existing cracks in the ice. On cold black ice a bit less than 1.5", there will be lots of cracking noise and many visible cracks forming in the ice near you. You need to turn back quickly and head for thicker ice. Otherwise you are likely be using your ice claws in short order. Thin, moderately thawed ice is generally much quieter. Careful observation of the ice and frequent use of your test pole will let you identify ice that is too thin before you get on it.

New black ice that is 3" or less can be very quiet if it is thawed. This thawing is often driven by sunlight and warm temperatures. It can weaken a lot of ice to below the breakthrough strength quickly, especially at lower lattitudes and late in the season. I have seen this happen on new fall ice in late November and in a late freeze in February or March. At 45 lattitude, the power of the sun is about 70 watts per square meter in late November and 600 watts in early March. If you can poke your test pole through black ice in one stab and the ice is quiet as you move over it, it is is probably in this condition.

Thawed Ice: Ice that has been exposed to above freezing temperatures or strong sunlight melts in a couple of different ways. If it is warm, windy and cloudy the melting will take place mostly on the top surface, thinning the ice. A windy 50 degree day can melt two or more inches of ice. In sunny conditions significant internal melting can occur. This melting is mostly at the grain boundaries. Occasionally melting can take place underneath the ice when there is an active underice erosion process (gas holes, reef holes, currents, etc). The water under the ice in shallow ponds can be heated sufficently by prolonged sunlight to warm the water and melt the bottom of the ice sheet (this is most pronounced in the spring).

Thin ice (less than 4") can can thaw enough to get significantly weaker in a few hours (or less if it is very warm or the ice is thinner). Thick ice at the beginning of a warm spell will usually remain strong enough for skating for between a day and, maybe, as long as a week.

About half the 2013 North American ice season fatalities involved thaw conditions. The three skating fatalities all were in thaw conditions. In seven other accidents it seems clear that the victims went out on the ice in the morning when the ice had hardened up overnight (overnight ice) and and stayed on the ice in warm conditions until it was too weak to hold them up. This is particularly common with fishermen.

The following are some of the stages ice goes through as it thaws:

Puddle Stage: Puddles form on the surface from melt water or rain.
Dry Surface: Grain crystal junctions melt through ice sheet and the puddles drain. The surface is often more textured.
Weakening Stage: As the grain boundaries continue to melt the bond between the individual grains gets weaker. Small Grain Ice (type S2) weakens dramatically more than Large Grain Ice (type S1).
Rotten ice stage: When you can punch through several inches of ice with your test pole in one stab. This stage continues until ice melts, usually with the help of wind and waves.

Cold weather will stop or reverse this progression. It is common for cold overnight temperatures to make a thawed ice sheet look like cold ice however only the surface layer is refrozen so if the ice was well into the weakening stage the previous day there is a good chance it will be again as soon as the thin overnight layer of cold-hard ice softens.

General advice on thawed ice:

Stay off thawed ice unless you are well equipped, experienced and willing to get wet.
Use your test pole a lot to keep track of the ice around you and how the thawing process progresses during the day. The pole is the most effective way to assess the approximate ice strength. Expect some areas to weaken faster than others (eg small grain ice, already thin areas, gas hole roofs, south facing rocky shores, etc)
Don't push your luck, when the ice gets sufficiently thawed it can be so weak that it is quite difficult to get back on the ice.

Nighttime skating: If you are thinking of skating after dark, the likelyhood of falling through is much greater and your ability to rescue yourself and others is significantly worse. (more on Ice at Night)

A few Ice Terms (see the glossary for a lot more):

•Black ice: clear lake ice

•Snow Ice: Frozen snow slush on the top surface of an ice sheet.

•Meringue ice: weak ice made from partially saturated snow builds up from loose snow blowing over wet areas. Common over gas holes, wide wet cracks and folded pressure ridges.

•Thawing: The process of ice melting. It occurs on the ice surfaces and internally.

•Cold ice: ice below freezing (even a little). Warm ice is at or very near freezing.

•Layered Ice: (Also called sandwich ice}. A sandwich of snow ice, slush, and/or water with black ice on the bottom. Occurs after snow submerges an ice sheet. Can be treacherous. Layered ice is only as strong as the black ice in the bottom layer.

•Splash-out ice: white ice from waves splashing shore or an ice sheet. A common indicator of former open water at ice edges and on recently refrozen holes.

•Overlapped pressure ridge: a rupture in an ice sheet caused by thermal expansion. One side of the rupture rides over the other. There is often weak ice or loose plates near the ridge. More on pressure ridges

•Folded pressure ridge: A ridge where the plates buckle down into the water rather than riding over each other. There is often a deep puddle in the center.

•Tectonic crack: a characteristic crack that is associated with ridges.

•Tight cracks: cracks that are closed at the top. An occasional source of tripping.

•Open cracks: cracks that are open at the top, even a little. A common source of tripping. (usually when the skate is closely aligned with the crack).

•Wet cracks: cracks with water in them, usually 1/8” to 1” wide but can be up to a foot or more on big ice (called Wide wet cracks).

Lead: a wide crack that forms when one part of an ice sheet seporates from other. Most likely to form when the ice is reasonably thin (few inches to a couple of feet), when the ice sheet is warming and when pressure ridges are forming. More:

•Dry shell ice: thin white ice that forms over a puddle that drained away. Easy to see so dry shell is only a moderate tripping hazard.

•Wet shell ice: thin ice over a puddle on top of an ice sheet. Hard to see and a significant tripping hazard. Usually found after a thaw.

•Overnight Ice: Ice that forms refreezes in cold weather overnight. It is the ice that forms new ice over holes or ridges or hardens the top inch or so of well thawed ice (typically in the spring).

Rotten Candled Ice: Very unreliable and unpredictable ice that occurs in fine grained ice in an advanced thaw condition. When you step on it, if you don't fall through, it gives a little as the vertical crystals shift. Skilled use of your test pole can often (but not always) identify it.

•Ice edge: where older ice meets open water or thin new ice.

•Hole: an area of open water that is surrounded by ice. Note: a hole is often still referred to as a hole after it has a thin skin of ice over it.

•New-ice hole: a common hole found in new black ice.

•Gas hole: formed by persistent sources of marsh gas. Most common over river deltas.

•Drain holes: from water draining through an ice sheet. Most common in ice less than a few inches thick after a wet thaw.

•Reef hole: hole or thin ice over shallow spot in other wise deeper water

•Current hole: place where current keeps the water open. Common under bridges, in rivers and in lakes that have river like attributes.

Ice Strength

•Cold and slightly thawed black ice generally have approximately the same strength. Old black ice is as strong as new black ice (contrary to much www ice advice).

•Cold, well saturated, snow ice is as strong or stronger than cold black ice. In warm conditions, snow ice can weaken quickly.

•Thawed ice gets progressively weaker with continued thawing. It becomes very weak in an advanced thaw condition. Snow ice and small grain ice get the weakest in an advanced thaw condition.

Tripping and falling is the major source of injuries.

Most of us fall once every few outings. Usually no harm is done. Protective gear helps (helmet, knee, elbow, wrist, hip, coccyx). Careful skating will reduce your chances of a fall.

Foot Traction: Getting to and from the ice often requires walking over irregular, sloped ice at the shore. Some sort of foot traction is highly recommended. Microspikes are currently the most popular. They have good grip on ice and shallow, loose snow and they are easy to put on and take off. They are reasonably resistant to falling off (I have had one come off in about 20 miles of walking).

Things to trip over:

•Partially frozen snow slush in snow drifts

•Snow drifts and styrofoam snow

•Open dry cracks

•Tight dry cracks sometimes break a piece out under the pressure of the skate blade

•Wet cracks. Narrow wet cracks can catch a skate. Wide wet cracks (1"-18") can fit a leg or a whole person.

• A skating pole planted in front of a skate while you are in motion often results in a hard fall.

•Small Holes

•Rough ice

•Vertical offsets in the ice (eg wave cracked ice)

•Crossing ridges or ice rubble.

•Wet shell ice (harder to see than dry shell)

•Dry shell ice

•Sticks/rocks/vegetation frozen onto the ice have a lot more drag on the skate blade than on ice.

•Skating into a deep (1+”) puddle

•Whisker stays on big iceboats are renowned for tripping people who walk up to a parked boat for a better look. Whisker stays are small diameter cables that run from the bow to the end of the plank at ankle height.

•Getting crossed up in an emergency stop or turn

•Getting too far back on your skates

•Sudden changes in wind speed on a windy day, especially when standing in one place on skates or with shoes with no foot traction.

•Trying to skate backwards on Nordic Skates.

You are more likely to be able to step out of a fall if you are skating than if you are coasting on both skates. Coasting on both skates is common when people are going down wind. Tripping at high speed can result in a particularly hard fall.

NOTE: Something we have learned from hard experience is DON'T carry things in front pockets in pants, shirts, front packs, parkas, etc. When you hit the ice in a hard fall they focus the impact energy in a small area. Wallets, cell phones, car keys, cameras, wate bottles have all cause pain, bad bruises, lost skating days, broken cameras, and, in one case, a lacerated liver (from a water bottle). It is best if things are in a back pack or off to the side irather than in front.