New Ice Holes (Warm water holes):
New-ice holes occur a bit less than half the time in new ice sheets. They stay as open water for hours or days followed by a period of being thin ice. They are a common source of swims for skaters and sailors.
What we call New Ice Holes typically range from a few feet to about 100 feet in diameter. Bigger holes than that tend to be much bigger (hundreds of feet to miles) and are better described as polynyas or 'open water'.
When the ice first freezes it usually does so during a cold snap in calm conditions. There will often be small areas that do not freeze over until several hours to a couple of weeks after the main ice sheet forms. New-ice holes often stay open for days to as long as a week or more partly because early season cold snaps are often followed by above freezing weather. Characteristics of new ice holes include:
- They are usually roundish in shape.
- They are associated with first ice.
- Often are in groups. If you find one, expect more.
- They often have a ring of white ice on some or all sides from wave water that splashed out and froze on the downwind sides of the hole.
- When these holes do skin over they are typically one to 4 inches thinner than the surrounding ice for the first few days.
- When they freeze, they may not all freeze at the same time. Sometimes only part of a hole will freeze. Treat each hole as though it be too thin.
- The ice sheet near the edge of the hole is usually nearly full plate thickness to within a few inches of the edge. Some other types of holes can have more tapered edges (eg gas holes and reef holes)
- When they are open they can be easy to see with the sun at your back and some wind to make the open water dark. On the other hand on a cloudy day, or if there is no wind or if it is sunny and windy but they are between you and the sun they can be hard to spot from a moderate distance. If there are puddles on the ice, they are especially hard to spot.
- Once they skin over they are much harder to see and you have to look closely for darker ice and for white splash out rims. There is often a slight step at the edge of the rim that can help with identification.
- Once they skin they seem to thicken as fast as a normal ice sheet.
- If the wind is light, it is common to have frost roses on a new skin and nearby ice. Frost roses are a fairly reliable indication of nearby open or recently skinned water.
- They are often attributed to springs on the bottom of the lake but, since they do not form in the same place year after year, that is not the case.
- If it snows after they freeze but before they get thick they become a booby trap as you can’t see them and the snow insulation slows the rate of thickening.
New-Ice holes are a very common source of new ice swims. If you are walking or skating watch carefully for the white slash-out rims and, sometimes, darker color where the ice is thinner. The outline of the hole can often be seen. An ice pole is needed for testing how thick they are. If you are moving quickly over the ice in an iceboat or snowmobile they come up too fast to avoid. We have generally found the only way to be sure they won't be a problem is to carefully check out the area before we go sailing. Observing the ice shortly after it freezes can give a good idea of where to expect problems. In rough terms we find new-ice holes on new ice a bit less than half the time. They seem to be more likely when the ice freezes earlier than usual. They are not just a early season phenomena. We find them in ice that forms on deeper parts of the lake in mid winter.
It is easy to see that wind driven convection is likely to be a factor in why they do not freeze. Convection currents in the water may also can create them. The southern end of Lake Champlain has enough flow through it to have a bit of river-like convection and we often find new-ice holes there early in the season. We suspect that there may be other mechanisms that create and sustain these holes but we have not found good supporting evidence for mechanisms other than wind and currents so far.