The posted coords will take you to the center of Lake St. Croix, a riverine lake which formed as the result of the natural sediment deposition and damming process which takes place as a river matures.
The Mississippi, Minnesota and St. Croix Rivers were carved over 11,000 years ago as proglacial lakes Agassiz and Duluth drained at the end of the last Ice Age. These glacial lake outburst floods were cataclysmic in magnitude. Torrents of water raged across this region for over a year before these giant lakes were drained. Deep gorges and valleys were carved. Upper substrate was eroded. The force of the these rivers cut deeply into the faultines down to the most resistant layers of bedrock.
These active glacial rivers are classified as a “young” or “youthful river”. A youthful river is a river with a steep gradient that has very few tributaries and flows quickly. Its channels erode deeper rather than wider. The gradient is controlled primarily by tectonics. The discharge is controlled by climate. The sediment load is controlled by various factors including climate, geology in the headwaters and the stream gradient. Fast moving water is capable of carrying, or suspending, a much greater volume of sediment than slow moving water, thus enhancing it ability to cut a path through varying stratas.
As time passed and the glacial lakes drained, the volume of water flowing through these channels has greatly reduced. These rivers are now classified as a “mature river.” The gradient has become less steep than those of youthful rivers and flows are slower. A mature river is fed by many tributaries and has more discharge than a youthful river. Its channels erode wider rather than deeper. As the speed of the water slows, the ability to suspend particulate matter also declines. The original deeply incised channels of the river valleys begin to fill with sediment. Sediment begins to accumulate and form deltas where tributaries meet the main river flow. This ongoing cycle continues to alter the flow and course of the maturing rivers. These tributary fans dammed the main rivers, forming riverine lakes.
The gradient and flow rate of each river is unique and subject to weather and watershed. The flow rate of the Mississippi was so greatly reduced that the ongoing deposition of sediment nearly dammed the St. Croix River at the confluence at Prescott, WI. The accumulation of river debris and sediment is now known as Point Douglas Park. The hydraulic damming action of the reduced flow, and subsequent backfilling, caused the formation of Lake St. Croix which extends from Prescott, WI northward through Stillwater, MN.
The following tasks are required to log this EarthCache:
Please forward in an e-mail the following:
1. An estimation of the width of the active channel of St. Croix River from the end of the causeway to the Minnesota shoreline, and reference your unit of measurement;
2. The elevation reading at GZ on the causeway;
3. The distance you walked from the arch to the posted coords; and.......
4. Posting a photograph of yourself or GPS at this site is now an optional requirement. Posting interesting photographs of this glacial footprint to educate other visitors to this EarthCache and to document your experience here are appreciated.