Lake and river ice is an amazing, dangerous, and wonderful thing. My home office overlooks the Duluth harbor with a view out to Lake Superior on one side and the St. Louis River on the other. This winter when I take breaks from working at my desk, I look out at the forming, drifting, breaking, and piling ice and see more than simply ice. The formation of ice on lakes is important due to its influence on lake biology, shore structure, navigation, and recreation. It is also a source of economic cost due to the shore and infrastructure damage it can cause.
Lake Ridden crack 32 bit
Ice is all around us in winter in the temperate zone, but I doubt many of us consider how it is formed. We talk about ice-up of lakes as if it is a singular thing. In reality though, it happens in many different ways and may be very different in the same lake in different years. The cyclic nature or phenology of ice-up makes a huge difference in the quality of the ice and changes the under-ice environment as well as the safety of lake ice cover.
Water molecules are composed of two hydrogen atoms that are each attached to the same oxygen molecule in a triangular formation. In liquid water, these molecules arrange themselves randomly. In ice, the molecules align themselves in a regular lattice pattern and are more spread out, which results in ice being less dense than water. Because the crystal lattice allows a lot of light to pass through, the under-ice environment is surprisingly bright. Aquatic algae and plants can grow under lake ice.
After ice-up there is usually a time period when ice cover looks good but is highly unsafe. People may also mistakenly assume ice thickness to be fairly uniform across a lake, but this is far from true (Brown and Duguay 2011). Bengtsson (1986) measured ice thickness in many places across several lakes and found that ice thickness could vary by more than 50%, especially when stream inflows or outflows are within a mile or so. Variations in ice thickness result from the way in which ice is formed and what happens to it over the winter.
In-shore ice forms first so may be thickest once a lake is completely covered in ice. Bays and harbors that freeze rapidly in the early winter may also initially be thickest. As winter proceeds, ice thickness can tend to even out across a lake (Bengtsson 1986). For example, when snow drifts onto thinner ice, it can slow the thickening of that ice through insulation. While the thicker ice continues to slowly grow thicker, the now-insulated thinner ice is also growing thicker more slowly.
Caution is always advisable when working or recreating on ice. When my grandmother was a child, their family lost two teams of horses through the ice on the lake where I grew up. I know exactly where they went in because, due to groundwater or other currents, that area which is about 100 feet from shore still always has thin ice.
Anchor ice is usually formed under currents or stream flow when super-cooled pieces of frazil stick together and stick to the bottom forming a bottom layer of ice. This is formed frequently in streams and rivers when water is supercooled but also can form in lakes (Kempema et al. 2001). In all cases, release of anchor ice transports a lot of sediment and can cause impairment of power generation and habitat.
The cracking of ice sheets forming leads that refreeze and ratchet expansion of ice sheets beyond shores. Ice jacking can cause creeping damage to shores over a protracted period (Kavanaugh et al. 2019).
The event denoting the loss of ice cover in river and lakes. Break-up can take place over several days or seemingly instantaneously. In lakes break-up is driven by wind and warmth whereas in rivers it is driven by meltwater flow. Normally smaller water bodies that have been fully ice covered lose ice earlier in the season than large ones.
Because in all but the largest lakes, ice melts fastest near shore, lakes form a shore lead or open space between the ice sheet and the shore. When wind blows across the ice sheet it will develop a terminal velocity of about 3% of the wind speed. Thus, ice sheets can develop tremendous momentum (momentum equals mass times the square of velocity) (Ashton 2010). It only takes about 4 cubic yards (about 8 square yards) of melting ice to have the same mass as an average skid steer. Considering a 30-mph breeze, the ice could have a velocity of about 1 mph or about the same velocity of a skid steer while working. Therefore, ice-push can do a lot of damage to shore infrastructure but also creates natural ice ramparts along shores (Wagner 1970). The distance ice will push inland increases with the wind velocity, the size of the floe, and the density of the ice, and decreases with the angle of the shore slope and the floe thickness (Ashton 2010). The height the ice will move up onto the shore or the height of a pile of ice increases with the wind speed and the size of the ice sheet and decreases with the height of the shore and ice pile above the water and the angle the shore and ice-pile rises above the horizontal (Tsang 1974). This implies that ice-piling is somewhat self-limiting.
Shoreline berms of terrestrial materials caused by ice-push. These occur most often in lakes greater than one-half mile in diameter with even shorelines, moderately sloping bottoms (about a 10-30% slope), and shore sediments that are sand or gravel (Wagner 1970).
A seismic event caused by a sudden cracking and failure of lake ice due to sudden expansion of an ice sheet due to quick atmospheric warming exacerbated by low snow conditions and high water levels. Some of the largest of these have registered 2.0 on the Richter scale (Kavanaugh et al. 2019), equivalent in local force to many earthquakes. Icequakes can cause extraordinary damage to shores.
A wall or ridge of hummocked ice where floes are pressed together or floes are pressed against fast ice. In smaller lakes, these often occur near ice-out at the mouths of bays or at the interface of large basins.
After 75 kilometres on the lake, I noticed two dark silhouettes in the distance. It was David and Maxwell, heading back to Severobaikalsk. Too much condensation was forming in their tent and it was soaking their gear as a result. We stopped to chat for a while and arranged to meet two weeks later in a warmer place to share a beer and some stories from the lake.
After resupplying at Ust-Barguzin, the plan was to cross the lake again and follow the western shore down to Listvyanka, and the end of my journey, around 400 kilometres south. The road was supposed to be straightforward, as there are some tourists in that area. I left Ust-Barguzin and got back on the lake, feeling pretty confident about the days ahead, especially since I was told the ice was snow-free on the opposite shore. I headed west with a dream of gleaming ice, my face layered with sunscreen and my bags packed full of biscuits to keep me going.
Around 50 kilometres down the track, I encountered a massive crack in the ice so large that it made it impossible for cars to continue further on. I hauled my bike over it, hoping to catch the road on the other side, but the trail had disappeared under a fine layer of snow blown in by the relentlessly strong wind. I knew there had to be another route, but spotting it was hopeless on a surface so flat and uniform. I decided to set up camp on the ice and start pedalling through the snow early the next morning.
Lake Champlain virtually laps at your feet for long sections of the 13.4-mile Island Line Rail Trail. Rolling through waterfront parks in Burlington and Colchester, the trail crosses the lake on a spectacular 3-mile causeway that requires a ferry ride to cross a 200-foot gap to destinations on South Hero Island.
"So the vapor precipitates out by clinging to microscopic particles in the air, such as sodium or calcium, and forming crystals," Mark Seeley, a climatologist at the University of Minnesota, told LiveScience's Life's Little Mysteries in 2011. "This is just what goes into the formation of snowflakes." [Photos of Snowflakes: No Two Alike, of Course]
Frost quakes typically strike after a cold snap rapidly drops temperatures well below freezing. The quick freeze makes ice in the ground swiftly expand and crack, producing loud booms. Though frost quakes sometimes shake the ground, their effects are localized, so the tremors are rarely caught on earthquake monitors. A similar phenomenon called ice quakes can loudly crack the ice in lakes and rivers.
Bubbles can make any scene seem like a fairy tale, but they pop in the blink of an eye. That's not an issue when temperatures dip below about 9 to 12 F (about minus 11 C), and you can make the bubbles freeze. The trick is to blow them up in the air so that they have time to freeze before hitting the ground or another surface. The bubbles will form crystalline patterns and some might break, looking a bit like the shell of a cracked egg.
Summary: Wind blowing off an ice edge may seem like it will not do much damage to an ice sheet, however cracks in the ice sheet or under ice melting can cause a lot ice sheet loss in a few hours, even in fairly light winds.
While this was counter intuitive at first, we figured out that the north wind was pulling the surface water away from the south facing ice edge. This pulled up warmer water from deeper underneath the ice as shown in the following diagram. It is also possible that most of the ice loss resulted from waves refracting around Thompson's point just to the west of Town Farm Bay. These deminished waves could have wave-cracked the thin ice sheet near its edge, cutting loose the pieces to be blown downwind into the open water.
Closer shot of the ice edge. Based on our limited experience with this, it appears to be more a problem with thinner ice. Contraction cracks and, perhaps more importantly, wave-break cracks that form in the intact part of the ice sheet probably assist the break up process. Waves in long-fetch open water can easily refract around land to roll in at diminished size in directions that are quite far from the wind direction. Temperature measurements made at ice edges with an off shore wind in shallow water (see Slushball article) showed a water temperature of around 33 deg, not a lot of energy for significant underice melting. In other circumstances higher water temperatures have been found. More work needs to be done to sort out which mechanisms are important however for the ice traveler, the outcome is the same: an off edge wind can remove a lot of ice from an ice sheet fairly quickly. Occasionally someone gets an unintended ride on a liberaged ice flow. 2ff7e9595c
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