Much of the today’s landscape in Barnes County, North Dakota is the result of continental glaciers that covered the area thousands of years ago during what’s called the Wisconsin Glacial Episode. The Wisconsin Glacial Episode was the most recent glacial advance of the Pleistocene Epoch (often called the Ice Age) that began 2 million years ago and ended about 12,000 years ago with the last glacial retreat. During the Pleistocene there were times when glaciers advanced due to cooler temperatures (called glacial) and periods when glaciers retreated due to milder temperatures (called interglacial). During the last glacial episode, temperatures were probably 4 to 5 degrees Celsius colder than they are today.
In North America, Pleistocene glaciers first formed in the higher elevations of the Rocky Mountains and in Greenland and Canada where it was cold. The ice got so thick it began to grow and spread following the topography of the landscape. Eventually, these ice sheets met each other creating one enormous ice sheet that covered most of Canada and much of the northern United States. During the Wisconsin Glacial Episode in North Dakota, the continental glaciers covered the areas north and east of where the Missouri River flows today. Suffice it to say, at the peak of the Wisconsin glaciation, the entire extent of Barnes County was covered by several hundred feet of ice!
As indicated in the previous paragraph, as glaciers grow, they move and flow over the land. One may think of ice as a brittle solid, but the enormous weight of a glacier hundreds of feet thick actually causes it to deform itself under its own weight and in effect “flow.” Large amounts of rock and sediment are incorporated into the moving glacier and can be carried great distances by the flowing ice. Once the glacier starts to melt, these rocks and sediments are deposited. This material is referred to as glacial till. Glacial till ranges in size from large boulders to tiny particles of clay and is usually unsorted, meaning the different sizes of particles are randomly dispersed throughout the deposit.
Landscapes formed by glacial till deposited as the glacier was receding are called ground moraines. Sometimes the glacial retreat stalled (in other words, the rate of forward flow was equal to the rate it was melting), and more glacial till was deposited at the edge of the ice sheet forming irregular hills and mounds called end moraines. Other times, glaciers began to re-advance, pushing material ahead of it, also forming an end moraine.
The earthcache is located near the crest of the Luverne End Moraine in Barnes County, North Dakota. This end moraine was deposited during a minor re-advancement of the glacier in the Wisconsin Glacial Episode. The Luverne End Moraine traverses the extent of Barnes County in the north-south direction. The width ranges from less than one mile to over five miles and the average thickness is roughly 100+ feet. It is deposited on top of older glacial deposits.
For credit finding the cache, please your answers to the following questions.
1. Look to the north and south along the crest of the hill. How are people utilizing this high point of the terrain to their advantage?
2. Now look to the west. Approximately how far does this end moraine extend at this location (i.e. how far is it to the bottom of the hill)? For reference, the next overpass in that direction is one mile away.
3. Notice that the landscape of the end moraine is actually quite rolling and hilly. Why do you think that is?
Sources/Additional Information:
NDGS Ground Water Studies, Barnes County, Part I
Guidebook for a Geologic Field Trip Valley City, ND
End Moraines - End of the Glacial Ride
Introduction to Glaciation
