Joe Aragon, Mike DeNoon, Cliff Fenton, Scott Lessor, Cheryl Neal
What do you notice about the arrangement of the rocks and other sedimentary materials
found in the cut-away at our field stop in Elmo?
How is the arrangement of rocks and sedimentary materials at our stop in Elmo different
than the other cut-aways at sites we visited earlier?
Just as a reminder, here is a picture of the cut-away at our second stop of the day at Nine Mile.
And here is a cut-away at our fourth stop at Niarada.
What is different about the size and arrangement of the materials at these two stops compared to our stop at Elmo?
In the cut away at the Elmo site, you see a deposit with rocks of many different sizes, shapes, and colors. The deposit also includes fine grain sand, silt, and clay surrounding the larger pebbles and cobbles. The pebbles and cobbles are mostly smooth and round. The arrangement at this deposit is different from the previous sites. The rocks and sedimentary materials at this site are not in layers – they are mixed up instead.
What geologic activity caused the deposits at our Elmo stop to happen?
If water were the cause of this deposit, then the rocks and sedimentary materials would be separated in layers with the heavier rocks falling to the bottom.
Extension of the Flathead lobe created the terminal moraine at Elmo during the last glaciation about 12,000 years ago.
The deposit at this site in Elmo is a moraine, a feature associated with the furthest reach of a valley glacier. This moraine is from the Flathead Lobe, an extension of the ice sheets of 12,000 years ago.
As the glacier inches forward, it conveys and bulldozes the rocks and sedimentary materials below it and in front of it. It drops, or deposits, the materials as a curved line of hills. These are moraines. The farthest position of a glacier is called the “terminal moraine.” As the glacier gets smaller and pulls back or retreats up the valley, it may deposit small “retreat moraines” along the way.
View to the East of the Elmo Moraine with Flathead Lake in the distance.
Ice would have filled the picture during the last ice age.
The land in the close part of the picture is hilly – this is material left by the glacier as it retreated.
Imagine the edge of a valley glacier as being a 400 foot tall snout of a rock eating beast of ice. We’ll call him Elmo. As Elmo moves forward, he captures rocks and other sedimentary materials in his icy grip, grinding and scouring the rock beneath him. His snout reaches as far as he can go, and he pushes the materials forward into a pile.