Many South Dakotans are aware that the geology of SE South Dakota was heavily affected by glacial action some 12,000 to 15,000 years ago. The term “moraine” refers to the conglomeration of rocks, gravel, and pebbles left behind by the glaciers. Not as many people are aware that there are classifications of the moraine deposits. Please refer to the following descriptions of moraine. This deposit is one of the most obvious deposits that I have observed in SE South Dakota.
Long ago, the awesome force of glaciers or ice sheets would carve impressive valleys, such as the James River Valley, and would bulldoze wide swaths of the northern plains landscapes. The rock and soil picked up and transported by glaciers creates new landscapes as it is eventually deposited by melting and retreating glaciers.
"Drift" is the generic term for all glacially deposited material. The term is derived from the old theory that rock and soil deposits around the world were not produced by glaciers or ice sheets, but were deposited by the Great Flood of biblical fame.
Here's a short glossary of different types of glacial and ice sheet depositions:
• Glacial flour - rock ground to the texture of a fine powder. It usually flows out of a glacier as sediment in a glacial meltwater stream running from the glacier.
• Till - refers to an unconsolidated and unsorted mixture of sediment, clay, gravel, and rocks deposited by a glacier.
• Moraine - a French word that refers to any glacier-formed accumulation - there are a variety of moraines.
• Terminal moraine - an accumulation at the outermost edge of where a glacier or ice sheet existed.
• Recessional moraine - moraine located "behind" the outermost edge of a glacier, formed when the glacier lingers in one spot for a long time.
• Ground moraine - gently rolling hills and plains deposited by ice.
• Lateral moraine - ridges of till on the sides of a glacier.
• Medial moraine - a moraine formed when two glaciers merge (a tributary and trunk glacier) and their lateral moraines come together to form a single moraine.
• Push moraine - a moraine created by till that was a moraine deposited by an earlier glacier that once covered the area.
• Ablation moraine - a moraine formed from material that fell upon the glacier.
• Glacial erratics moraine - large boulders that had been carried by the ice and deposited. They are much different in size than surrounding till.
To complete this earthcache, please supply answers to the following questions:
Q1: What is depth (in feet) of the primary deposit of moraine at this site? Is it a heavily or sparsly filled layer?
Q2: From the descriptions given, what type of moraine is shown here?
Q3: What is the depth of the clay soil in the bank (above the bottom of the road ditch)?
Q4: Describe landscape at the site and to the west of the site.
Q5: What is the elevation at Ground Zero?
This cache is within a public or roadside area. It is located along a road on the east side of the James River, and is part of a trail several miles long within Yankton County. No need to cross fences or enter private property. Take care to park safely and pay attention to traffic conditions.
This cache was first made available to attendees of the 4th Annual Yankton Spring Caching Event. It will be published for the general community on Saturday, May 4, 2013.
Do not post pictures of yourself with the GZ in the background; this makes it possible for other cachers to complete the questions without visiting the site.