The Formation of Lake Pepin EarthCache
Hidden : 7/6/2008
Difficulty:
1 out of 5
Terrain:
1 out of 5

Size: Size: other (other)

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Geocache Description:

Geological Marker on Highway 61


At the posted coordinates you will learn about the formation of Lake Pepin.

As you may be aware, Lake Pepin is simply a wide part of the Mississippi River. But what happened to widen the river, fill in the gorge, and make it into a lake?

To log this earthcache you must...
  • Read the marker at the posted coordinates and email me (Please include the word "Earthcache" in your message) the answers to the following questions:
    • Look one mile to the East. You will see where the Chippewa River empties into the Mississippi on the Wisconsin side.  What specific characteristic of the Chippewa River does the marker say made it important in the formation of Lake Pepin?
    • Take a look at those high bluffs behind you, and all up and down both sides of the lake.  What does the marker tell you they are composed of?
    • How long do you think it took for the walls to be carved by the river?  During what geological periods does the marker say the deposits forming those wall were left?  How long ago was that?
    • BONUS: Which depositional environment listed below do you think is the key to the formation of the lake?
  • Upload a picture of yourself at the geological marker. [In compliance with new rules at earthcache.org, this is now OPTIONAL.]

DO NOT POST THE ANSWERS IN YOUR LOG OR IT WILL BE DELETED.

About sediment and sedimentation (from wikipedia)
Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid.

This process of sedimentation takes place in six major depositional environments:
  1. deltas - A delta is a landform where the mouth of a river flows into an ocean, sea, estuary, lake or another river.  A delta is formed only when a channel deposits sediment into another body of water.  It builds up sediment outwards into the flat area which the river's flow encounters (as a deltaic deposit) transported by the water and set down as the currents slow.
  2. point bars - A point bar is a depositional feature of streams.  Point bars are found in abundance in mature or meandering streams.  They are crescent-shaped and located on the inside of a stream bend.  Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream.  They also have a very gentle slope and an elevation very close to water level.
  3. alluvial fan - An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
  4. braided rivers - A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars.
  5. oxbow lakes - An oxbow lake is a U-shaped lake water body formed when a wide meander from the mainstem of a river is cut off to create a lake.
  6. levees - A levee, floodbank or stopbank is a natural or artificial slope or wall, usually earthen and often parallels the course of a river.

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