Geocache Description:
Map #57 – Very low gradient path along abandon Portage Canal which connects the Fox (to the northeast) and Wisconsin (to the southwest) Rivers. The marked Ice Age Trail goes away from the canal through city streets for part of the trek. There was once an active lock system which allowed boats to travel between the Wisconsin and Fox Rivers.
Equipment: GPS, Compass
Educational Information:
A Hydrological Divide (also called a Continental Divide) is a separation of watersheds which results in water draining in different directions to different bodies of water off the continental shores; (eg: Gulf of Mexico / Atlantic Ocean).
Precipitation that falls just inches apart on the ground will follow paths through different river systems to the seas / oceans. These waters are on distant coast lines and different sides of a continent.
Most people know of the “Great Divide” in North America. It is located in the Rocky Mountains and separates watersheds heading west to the Pacific Ocean and east to the Rio Grande and Mississippi Rivers, eventually entering the Gulf of Mexico. It's a myth, however that a continental divide must be in a mountainous area. Several other hydrological divides in North America are relatively flat in many areas.
The St. Lawrence Seaway Divide can be found near the city of Portage and is shown in orange at this location on the divide graphic. This divide separates south flowing water in the Wisconsin River basin (flowing to and along the Mississippi to the Gulf of Mexico) from the north flowing Fox River basin (flowing to Green Bay and through Lakes Michigan, Huron, Erie, and Ontario to the St. Lawrence River and the Atlantic Ocean.
Such geologic sculpting of the landscape impacted human history. The Fox – Wisconsin River portage was an important junction for the fur trade industry in the mid 1700’s. Protecting this trade route was of vital importance to the British in the American Revolution. Much of the surface close to the canal has been modified by human activity with the canal between the Wisconsin and Fox Rivers being the most significant. The surrounding area is sediment deposited by slow moving water, mostly sand and silt, with a thin cover of marsh deposits. The combination of a very low, natural gradient and human modifications makes it difficult to locate the high point dividing the Fox and Wisconsin Rivers watersheds; however, it is easy to determine which river is relatively higher in this area.
The number and position of continental divides can be dramatically changed over time. Tectonic forces can raise mountain ranges. Climatic forces may expand glaciers and block drainage outlets.
The Niagara Escarpment was a factor in splitting the Green Bay and Lake Michigan lobes of the most recent glacier and creating the moraines throughout the Kettle Moraine area of today. The moraines along the western and southern edges of the Green Bay lobe of the glacier were then a factor in creating the St. Lawrence Divide.
A canal lock chamber will have an upper and lower pair of mitre gates. The gates will close against each other to create an 18° angle. This angle approximates an arch against the water pressure on the upstream side when the water level on the downstream side is lower.
IATCC is the cache designation to highlight a series of EarthCaches along the Ice Age National Scenic Trail grouped into a special category called "ColdCache."
The Ice Age Trail is one of eleven National Scenic Trails in the country. This unique trail is entirely within the state of Wisconsin and follows along the terminal moraine of the most recent glacier which retreated about 10,000 years ago.
The Cold Cache project is supported by the Ice Age Trail Alliance (IATA). The goal is to bring more visitors to the Trail and promote public awareness, appreciation, and understanding of Wisconsin’s glacial landscape.
The IATA has created an awards program to encourage visits to the Trail and ColdCache sites. This awards program is separate from, and in addition to, any other Geo- or EarthCache awards program.
A current list of approved ColdCache sites can be found on the “IATCC Bookmark List”. More information on the Ice Age Trail ColdCache Project can be found on the “ColdCache Webpage”.
Resources: Wikipedia, Geology of the Ice Age National Scenic Trail; by David M. Mickelson, Louis J. Mahler Jr., and Susan L. Simpson, Northwest Territory Alliance
From Geology of the Ice Age National Scenic Trail by David M. Mickelson, Louis J. Maher Jr., & Susan L. Simpson. Reprinted by permission of the University of Wisconsin Press. © 2011 by the Board of Regents of the University of Wisconsin System. All rights reserved.
Logging Requirements
Walk along the Ice Age Trail to the foot bridge just south of the parking area. From here, the Fox River is to the northeast. Look for indications of the direction the water is flowing. Continue along the IAT to the southwest until reaching the canal gates near the Wisconsin River. Somewhere along the route, you will be crossing the St. Lawrence Seaway Sub-continental Divide.
- Along the route, were you able to determine which way the water was flowing? HINT: It may help to toss a small twig or pieces of grass into the water; however, a wind may cause the item to flow upstream.
- Were you able to determine where along the route you crossed the divide?
- Observe the canal gates near the Wisconsin River. Based on the angle of the gates, which river (Fox or Wisconsin) has the higher elevation?
- Were you able to estimate how much the elevation changes between the two rivers? How?