Geology of Deer Creek

Over 12,000 years ago much of the Nemadji River Basin, including Deer Creek, was submerged beneath Glacial Lakes Duluth and Nemadji. The lakes drained and left behind glacial lake (lucustrine) deposits of clay, silt, and very fine sand. Additionally , glacial ice deposits left behind glacial clay till. Today, apporximately one half of the Deer Creek Watershed is comprised of glacial till and lake laid clay soils.

The complex geological setting of the Deer Creek Watershed and greater Nemadji River Basin has been studied by many researchers. The geological history of the area helps researchers understand current hydrological behaviors in the watershed. Geomorphology (shape of the land) is closely linked to the understanding of t he hydrology (movement of water). Stream water pathways through land are resposible for sediment transport, including erosion and deposition. Additionally, groundwater pathways to the stream can contribute to sediment loading in a stream channel, which is the case in Deer Creek. The locally known “Mud Volcanoes” contribute sediment to the stream via groundwater.

While the turbidity TMDL study ultimately seeks to define the sediment load of the stream, the borader system functioning of the stream and watershed much be considered. A geomorphology and channel assessment investigation will provide valuable information about processes such as erosion and slumping.

mud volcanoe                                        mud volcanoe 2

Erosion

A stream channel is formed through erosion and deposition. High flows are responsible for doing the work of channel formation and maintaining the channel over time. Historical land use changes have likely increased the water yields in the system. This influx of water has caused more downcutting and incision in the stream channel, causing more sediment loading to the system (Reidel, Verry, Brooks 2002).

Slumping

Tree splits such as the one displayed below, are a result of a rotation slump. Half of the tree roots were taken down slope with the land while the hother half remained at the original location. The continued movement of the land down slope hled the tree roots and cause the tree to topple upslope. These types of slumps are common in the lucustrine clay protion of the watershed.

slump                                                                       slump diagram