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Glacial Origins of Iowa's Great Lakes

A cache by lagrac Send Message to Owner Message this owner
Hidden : 5/8/2009
In Iowa, United States
2 out of 5
2 out of 5

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Geocache Description:

This EarthCache is located on the shores of West Lake Okoboji in Lazy Lagoon Park in Triboji Beach. Parking is close by and the views of the lake from this little park are lovely.

13,500 years ago, as the glaciers of the last Ice Age retreated, the Des Moines Lobe left behind it's undeniable footprint on the landscape of Northwestern Iowa, forming the Iowa Great Lakes. Geologically, these lakes are a confluence of large glacial potholes.

The Iowa Great Lakes region was created along the southwest edge of an ice sheet that surged southward about 13,500 years ago, halting at what is now the city of Des Moines. This ice stagnated across the landscape and was followed by several smaller more subsequent advances over the next 1,500 years. The resulting topography in the lakes area is especially eye-catching because the younger glacial advances overlapped the older ice and merged to create widespread areas of high-relief, hummocky, "knob-and-kettle terrain." The irregular hills of glacial debris associated with these compressed ice margins are laced with sloughs, bogs, and wetland "potholes" which formed as a result of direct contact with the slowly disintegrating ice.

The Iowa lakes region also served as an important drainage outlet along the western edge of the melting ice sheet. One persistent route channeled meltwater southward past the Gull Point area, through the Okoboji Lake Outlet at its southern end, and into the Little Sioux River. Extensive sand and gravel deposits along this route are ample evidence of the huge volumes of water and sediment discharged by the melting ice.


The most notable of the Great Lakes is West Lake Okoboji. It is classified as a "Blue Water Lake". There are only three blue water lakes in the world: Lake Geneva in Switzerland, Lake Louise in Alberta, Canada and West Okoboji Lake in Dickenson County, Iowa.

A blue water lake is a lake in which the water is supplied from subterranean springs or source of fresh water rather than being produced by the collection of rainwater and runoff from the surrounding topology--actions that would produce a lake of murky and silt-laden water suspending all kinds of detritus.
West Okoboji Lake is the largest of a chain of five connecting lakes, which is considered part of Iowa's Great Lakes.

According to information obtained from the Iowa Department of Natural Resources, West Okoboji Lake is comprised of 3,847 surface acres of water with an average depth of 38 feet and maximum depth of 136 feet. There are 19.8 miles of shoreline around West Okoboji Lake and the natural drainage basin is fed by 13,668 acres of land or approximately 22 square miles. Three State Parks are located along the shores of West Okoboji Lake, including Pillsbury Point, Gull Point, and Pike's Point.

West Okoboji Lake was called "Minnetonka" by the Sioux Indians and translated into "Great Waters". The first settlers decided to use a version of the name "Okoboozhy" for both lakes known today as the "Okoboji" lakes.

Most lakes in this region are rounded, flat-bottomed and shallow, generally less than 20 feet deep. They likely formed as the glacial ice disintegrated and collapsed. West Okoboji Lake, on the other hand, is long and narrow in outline with numerous rounded bays and a maximum depth of approximately 135 feet - the deepest of Iowa's natural lakes. It is thought to have formed along a pre-existing lowland which became occupied by an enormous block of the decaying glacier.

To log this EarthCache, you will need to perform these tasks:

Please fill a clear glass container with a clean sample of lake water to examine the following:

  1. Please measure the pH of the sample.
  2. Please place a white sheet of paper behind the glass container and describe the colour of the water, and any sediment you have found then e-mail the results of your findings.
  3. Please post a photo of either yourself and your gpsr, or your gpsr near this lovely lakeshore.

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Current Time:
Last Updated: on 6/28/2017 11:38:51 AM Pacific Daylight Time (6:38 PM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum

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