Stream evolution, lake beds, and Minnesota rocks! Hydrology and geology at the market

Faculty and undergraduate scientists from the University of St. Thomas Geology and Environmental Science Departments lead our investigation of Geology, Hydrology and Paleolimnology last Saturday.

L to R: Sam Duncanson, Andrew Pilimai, Derek Robinson, and Professor Kevin Thiesson from the University of St. Thomas with their stream evolution demonstration (dubbed, for the day, STREAM SIMULATOR 3000).
L to R: Sam Duncanson, Andrew Pilimai, Derek Robinson, and Professor Kevin Thiessen from the University of St. Thomas (not pictured: Eric Stevens) with their stream evolution demonstration, dubbed, for the day, STREAM SIMULATOR 3000.

We learned about how topography can affect water flow and how water flow can influence topography. Many people donned 3-D glasses to examine a shaded topographic map that showed the mountains, river valleys, and undersea landforms of the whole globe. We saw undersea trenches, tall mountains, and the Mississippi River Valley. Then we used the U of St. Thomas’s stream simulator that allowed us to interact with water flow on a landscape and examine the processes that shaped those landscapes. We made eddies, formed potholes, and tried out sediment levies.

Small pieces of recycled plastic were used to simulate sediment, with water flowing in from the top of the tub, illustrating how water can flow through a landscape and lead to sediment deposition. Market visitors could alter the terrain and examine how water movement changed or watch as water pooled or moved under the sediment to create new landforms.
Small pieces of recycled plastic were used to simulate sediment, with water flowing in from the top of the tub, illustrating how water can flow through a landscape and lead to sediment deposition. Market visitors could alter the terrain and examine how water movement changed or watch as water pooled or moved under the sediment to create new landforms. Intensive modification of streams alters the water flow.

We tried our hand at paleolimnology, or the study of the history of lakes. We learned that soil cores from lake bottoms, or beds, can reveal the environmental history of the area. Sediment appearance changes with the seasons and can be examined to show the historical climate of the area using chemical analyses, pollen counts, and many other techniques. Some of the scientists were using the chemistry of shells in different lake sediments to reconstruct temperatures! We also looked at diatoms that are commonly found in lakes and sediments in Minnesota. Diatoms are algae with silicate (glass!) shells and their shells remain in soil and lake sediment after they die.

This is a picture of a lake core (courtesy of Dr. Thiessen) close to 1.5 meters deep collected from Roseville, MN. The core was collected with a long drill. The sediment changes in color seasonally from lighter to darker, and annual variation can be examined from looking through each layer in the core.
This is a picture of a lake core (courtesy of Dr. Thiessen) close to 1.5 meters deep collected from the bottom of a lake in Roseville, MN. The core was collected with a long drill. The sediment changes in color seasonally from lighter to darker, and annual variation can be examined from looking through each layer in the core.

We also looked at different types of rocks to learn about the geology of Minnesota. We examined the difference between sedimentary and igneous (volcanic origin) rocks with hand lenses and microscopes.  We tried to determine whether the rock was quickly cooled or slowly cooled based on the size of crystals (bigger crystals result when rocks are slowly cooled). We examined how metamorphic rocks are different from their composite parts (both igneous and sedimentary).

Rocks from throughout Minnesota.
Rocks from throughout Minnesota.

Finally, we took all of our new-found geologic knowledge and mixed it with googly eyes to make fine art! Thanks again to Dr. Kevin Thiessen and the scientists from University of St. Thomas. We had a total of 188 visitors this week (76 kids, 112 adults, and 118 people stayed long enough to alter hydrology and examine rocks or make their own pet).

Pet rocks made by market scientists!
Pet rocks made by market scientists!
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