Wood Rill SNA's Bufflehead Pond
As you hiked to this GZ, you are walking through Minnesota’s Big Woods. Stretching across southeast Minnesota, the Big Woods once covered 2,000 square miles. Mush of the maple bassword forest was cleared for farmland in the early decades of Euro-American settlement. Today, few significant tracts of Big Woods remain.
Wood-Rill SNA is one of those few. The forest here has reached old-growth status. You’’ find several large maple trees 200 years alongside oak, basswood and ash over 150 years old.
The Land of 10,000 Lakes is not necessarily a true statement, The actual number of lakes (greater that 10 acres in size) is more than 12,000. These lakes, along with our rivers, give Minnesota more shoreline than Hawaii, California and Florida combined.
All of these lakes have a glacial origin and are of one main types. Those of northeastern Minnesota, including those in the Boundary Water Canoe Area Wilderness and Voyageurs National Park, are scoured lakes, formed on glacially eroded bedrock. Lakes elsewhere in Minnesota (like this piece of water at the GZ), were formed in depressions on glacial deposits, many of which are kettles created where blocks of ice were buried.
Kettles may range in size from 15 feet to 8 miles in diameter and up to 120 feet in depth, although Bufflehead Pond currently is only about seven feet deep on average. Most kettles are circular in shape because melting blocks of ice tend to become rounded; distorted or branching depressions may result from extremely irregular ice masses.
Two types of kettles are recognized:
a depression formed from a partially buried ice mass by the sliding of unsupported sediment into the space left by the ice and
a depression formed from a completely buried ice mass by the collapse of overlying sediment.
By either process, small kettles may be formed from ice blocks that were not left as the glacier retreated but rather were later floated into place by shallow meltwater streams. Kettles may occur singly or in groups; when large numbers are found together, the terrain appears as mounds and basins and is called kettle.
Bufflehead Pond: About 16,000 years ago on this very spot, a massive glacier covered the land. As the climate warmed and the glacier retreated, a large ice block became trapped in the low spot you see here. A covering of glacial debris insulated it, so it remained long after the glacier disappeared. Finally, the ice block melted, forming a kettle shaped depression filled with water. Today we call this kettle lake, Bufflehead Pond.
In order to claim this earth cache as a find, you will need to send me the answers to the following questions. Apologies in advance, but if I do not receive your answers in a reasonable timeframe after you log your find, I will delete your log.
Questions:
- As you look at Bufflehead Pond, how do you think it took its shape?
- Do you think the volume of the water has changed since its creation? Why or why not?
- Assuming that Bufflehead Pond once was large enough to fill this entire depression, how many gallons of water are missing? To do this, lets treat this pond as a more rectangle shape. And then … Multiply estimated length (feet) x estimated width (feet) x the difference of the height of the current water surface and height of the entire depression (feet) x 7.48 gallons per cubic foot.
- Please upload a photo of Bufflehead Pond and your geocaching group as well. Optional, but always nice to see.
References:
Roadside Geology of Minnesota, Richard W. Ojakangas.
Kettle geology, on Britannica website.
Minnesota Scientific and Natural Areas homepage - www.mndnr.gov/snas
Minnesota Scientific and Natural Areas rules - www.mndnr.gov/snas/rules.html
Wood-Rill Scientific and Natural Area - https://www.dnr.state.mn.us/snas/detail.html?id=sna01087