Ice
Iced In
Written by: Lisa Ayers Lawrence, Virginia Sea Grant, Virginia Institute of Marine Science
Summary
Analyze actual and predicted ice charts and use them to assess the effects of ice on wintertime shipping in the Great Lakes.
Objectives
- Recognize the significance of ice in relation to shipping in the Great Lakes.
- Interpret egg code classification of ice.
- Compare ice distribution maps and discuss the effect of ice on shipping.
Vocabulary
Jetstream, Egg code
Introduction
The winter of
2003-2004 was bone-chillingly cold for many regions in the United States. One region especially
hard hit was the Great Lakes. December 2003 was a relatively mild month, with
temperatures averaging as high as 5 degrees above
normal. In January 2004, as is typical in the winter, the jetstream migrated southward
allowing cold Arctic air to come in from Canada. Temperatures in January
averaged 9
degrees below normal. With the plummeting temperatures, the Great Lakes began to freeze over,
resulting in major impacts on life around the Great Lakes especially for maritime
travel and commerce.
The Great Lakes formed approximately 14,000 years ago as the glaciers that
once covered North
America began to retreat. The lake system accounts for 20% of the world's
fresh water, making it the largest freshwater system in the world. It is
made up of five lakes, Superior, Michigan, Ontario, Erie and Huron, and is
bordered by eight states and two Canadian Provinces. The lakes are connected to
each other by three rivers, St. Mary’s, St. Clair and Niagara, and the Straits of
Mackinac. The St.
Lawrence Seaway provides the outlet to the Atlantic Ocean. A series of locks,
canals and channels allow ships up to 740 ft long to maneuver the Great Lakes.
The Great Lakes are a major shipping gateway, especially for agricultural and mine products, and yet it's not unusual
for Lakes Superior, Huron, and Erie to experience 70% or more
ice coverage during the winter. The NOAA Great Lakes Atlas maintains daily
average ice cover charts from 1973 through 2002 for Superior, Michigan, Ontario, Erie and Huron.
How does the
shipping industry deal with ice? Indeed, the locks between Lake Ontario and
Montreal on the St. Lawrence River do close from late December to late March
because of ice, but before and after this closed season, the Great Lakes have a
couple of methods to ensure that maritime commerce can continue even with ice.
The United States and Canadian Coast Guards employ icebreaking
tugs, vessels, and buoy tenders to cut paths through the ice. They also rely on
up-to-date ice data and ice prediction charts. Both the United States National Ice Center and the Canadian Ice
Service produce ice charts that use an "egg code" to explain the ice conditions.
The egg code is a
unique symbol that can convey a lot of information in a compact form. The egg
code is divided into four sections. The top section indicates how much ice
coverage is in a certain area of the lake and is depicted in tenths. If the top
number is 1, then 1/10th or 10% of the area has ice. The remaining three
sections are read in columns and describe the thickness (section 2), type of
ice (section 3), and the size of the chunk of ice or "ice floe"
(section 4). Go to the Canadian Ice Service Egg Code page to see a detailed
explanation of how to read an egg code.
In the following
data activity, we will analyze actual and predicted ice charts and use them to
discuss wintertime shipping in the Great Lakes.
Data Activity
>Print out the following 2002-2003 ice charts from the National Ice Center:
NOTE: You will need to use your "landscape" orientation to print the eastern lakes maps and your "portrait" orientation to print the western lakes maps. If you wish to compare the maps side-by-side on two screens, click on the icon which allows you to expand the map to regular size (it will appear on the page and will say “expand to regular size” when moused over).
How did the predicted January ice maps compare with the actual December ice maps?
How did the predicted March ice maps compare with the actual March ice maps?
Did any lakes completely freeze over?
Look at the actual ice conditions for March 27, 2003 eastern lakes and western lakes. As mentioned above, the Montreal/Lake Ontario locks open back up in late March. Imagine how much icebreaking would have been necessary to get to ports such as Duluth, Detroit, Toledo, and Cleveland.
Which major ports would be affected by the remaining ice?
Now let's look at the 2003-2004 season. Print the following maps:
How close are the 2003-2004 predictions to the actual values?
Did any lakes completely freeze over?
What is unusual about your answer to question #6, and how do you explain it?
Which ports would be affected by a frozen over Lake Erie?
