The Need for Eggs -- Beyond Culinary Satisfaction

In the kitchen, eggs and ice don't mix too well but in map-making they do; more specifically in preparing charts of ice coverage, commonly also known as "egg charts."

Ice on Lakes

In areas with extended periods of cold weather, the surface of lakes tends to freeze over at such times. Then people will venture out onto the ice as if it were solid rock. For many communities in the far north the only way to bring in supplies of large and heavy items is via winter ice roads across the many frozen lakes as there are no access roads over land. Even with ice a few feet thick, a heavy 18-wheel truck will add enough weight to depress the ice at its location when crossing a frozen-over lake. As a result, such trucks are constantly going uphill then. The main question though is whether the ice is strong enough to support the additional local weight. Of course, that depends both on the thickness and firmness of the ice, and applies equally to a man walking or a truck driving across it.

---

For these and other reasons, knowledge of ice coverage and its properties at any given time can be critical. Ice "egg charts" help to provide that information in a simple manner.

Egg Charts

Egg charts provide detailed information on ice coverage, ice thickness, density, strength and current trends. Such charts have been used for decades and are provided, free of charge, by various government agencies including the U.S. National Ice Center and Environment Canada for the Great Lakes and other areas with significant seasonal ice coverage. A recent egg chart is given below. It shows the eastern Great Lakes, including the Lakes Huron, Erie, and Ontario as well as parts of the St. Lawrence River and connecting waterways. As you can see, at the date (Jan. 30, 2014) Lake Erie (at the bottom of the chart) is covered with ice at 9/10^th or higher throughout and Lake Huron with Georgian Bay (top of chart) by well over 50% of its entire area. In contrast, the deep Lake Ontario (on the right) is essentially still free of ice except for its shallower near-shore areas. While the colors in this graph indicate the major sub-areas and their ice cover are easy to read, the numerous "eggs" spread along the sides give detailed information on the exact state of the ice in each area. They provide more in-depth information on the details of ice strength and cohesion. The grey areas indicate "fast ice" that is a solid uninterrupted ice cover attached to land. The Egg Code The egg code is a standardized representation of the ice in various parts of the Great Lakes as well as sea-ice in the Arctic and Antarctic, though it is somewhat different for the sea-ice. Let's look at one closer, for example the egg "O" found at the top left corner of the chart. It occurs twice on the chart showing that the ice properties are similar in both areas of Lake Huron. It is enlarged below. All numbers indicate values between zero (minimum) and 10 (maximum). In the specific egg shown, the top numeral (9) relates to the total coverage which is also apparent from the code for the red color on the chart. The "9" means that the coverage is 9/10ths of the lake's surface in the areas denoted by the letter "O." The row below the "9" contains two numbers, referring to the concentration in tenths of thick (first digit) and thin ice in the area. Together they add up to the top number. The third row describes the stage of development with the numeral 4 indicating ice of 5-15 cm thickness and the 1 ice of up to 5 cm thickness. The fourth row indicates the size of common ice floes with the first (first digit) indicating the size of large parcels and the second the size of small ones. In that row the 3 is indicating ice floes in the 20-100 m and size range and the X pancake sized ice parcels. As a rule of thumb, the higher the numbers in any field, the thicker is the ice, the larger are the floes and the stronger and more cohesive is the ice cover. More detailed information is available from NOAA. If you plan to venture out on the ice anywhere in the areas covered by the daily ice charts, it may be useful to have a look the appropriate "egg" beforehand, but if you just want to stay in the kitchen it suffices to prepare the eggs to your culinary satisfaction.