As the glacier crept over the underlying rocks, its base scraped millions of tons of creating debris composed of soil, pebbles, cobbles and boulders. The debris was pushed forward, grinding rocks into glacial dust, while boulders scratched their traces into the bedrock. As the glacier retreated the weight of the ice over the Michigan basin lessened. The earth began to rebound, like a sponge returning to its original shape. The Michigan landscape began to emerge as plants appeared on the exposed landscape.
The climate began to warm and the ice melted further. Meltwater carried the soils and rocks away from the melting glacier, depositing its “drift” or debris over the landscape. As this blend of soils and rocks was dropped away from the ice, the low hills, or moraines, were created across the state. The depth of glacial drift averages 200 to 300 feet across the state, ranging from over 1,000 feet in a few locations and no accumulation in others. The grinding of boulders created particles of various sizes and weights. The heaviest pieces fell first, forming stony ridge. Lighter materials were carried farther, dropping along the way as the flowing water slowed. These materials dried in sheets forming vast, flat multi colored areas of sand, silt, clay and a mixture of the three called outwash plains. Evidence of this process is seen at the south end of Lake Michigan in the Kankekee Outwash Plain.
Two particular glacial signatures can be seen here in Glacial Hills, drumlins and erratics. On the plains here in Antrim and in several other Michigan counties are curious long cigar-shaped hills known as drumlins. Drumlins occur in areas where the ice advanced over previously formed plains. They are elongate in the direction of ice movement and most of them have a front or "stoss" slope at the head end which is somewhat steeper than the lee slope. Drumlins are typically 1 to 2km (~.5 to 1.25mi) long, less than 50m (160ft) high and 300 to 600m (980–1970ft) wide.
An erratic is a rock or boulder that differs from the surrounding rock and is believed to have been brought from a distance by glacial action. Erratics are formed by the movement of ice. Glaciers crack pieces of bedrock off, producing the larger erratics. In an abrasion process, debris in the basal ice scrapes along the bed of the glacier, polishing and gouging the underlying rocks, producing smaller glacial till. Erratics which may be as large as a house often have been lodged in a prominent position in the glacier valleys or have been scattered over hills and plains.
To claim this earth cache please email me with your answers to the following questions:
1) What evidence do you see of drumlins here in Glacial Hills? In which direction do the axes of the drumlins indicate the glacial flow occurred?
2) As you walk along the trail to Waypoint 2, examine the exposed material composing the drumlins. What color and particle size do you see? The bedrock in this area is shale, a stone composed of fine particles which typically breaks into thin layers. Does the material you see reflect this source?
3) At Waypoint 2 you will see 2 collections of erratics. The first is at the given coordinates. The second is about 100’ further down the trail toward the overlook. Compare the appearance of the stones in the two groups. Are they similar in size, color, graininess? Are there the same number of stones in each group?
4) At Waypoint 3 you can catch a tiny glimpse of Bellaire Lake. As you look toward the Lake, what geologic features do you notice?