Figure 1.3: 8,500 years ago: Sandstone concretions emerge from surrounding Swan River Formation (SRF) by Lake Agassiz wave action and Lake Agassiz sand (LAS) was deposited.
Figure 1.4: Present surface: Following the drainage of Lake Agassiz the land surface emerged and was colonized by vegetation.
During the second stage, regional uplift raised the stratum above the level of the sea. At this time, percolating groundwater cemented loose bits of sand and sediment together to form concretions (Figure 1.2). Sand was cemented around a nucleus or centre-an unknown base, possibly a fossil. The "glue" or adhesive was a lime solution, derived from the calcium carbonate of sea animal skeletons. In this process called chemical precipitation, the concretions maintained the layered appearance found in the original stratum.
In the third and final stage-about 8,500 years ago-glacial ice of the last Ice Age had retreated into northern Manitoba. Lake Agassiz modified the land to look much like it does today. During the final drainage of Lake Agassiz, beaches, offshore bars and spits formed where the kettle stones were held in the soft sandstone. Waves crashed against the sandstone shore and eroded the loose material around them (Figure 1.3). The harder concretions or kettle stones were left behind with Lake Agassiz sand (LAS). Being firm and round, the stones weren't noticeably altered by the waves. Since then, wind, rain, heat and cold have weathered those that are above ground level. Some appear to be partly above the ground surface and an unknown number of others may be still completely buried (Figure 1.4). The remaining original sandstone stratum is about 10 m below the present sandy surface and extends through all of southwestern Manitoba.
Wave erosion by Lake Agassiz has left a unique landscape, with the kettle stones propped up like sentinels overlooking the Manitoba Lowlands to the east. While the origin of the name kettles is unknown, it is generally believed that they are so named because they resemble household kettles or kettle drums..
Although these kettle stones have not been weighed, the one at the Swan River Town Visitor Information Centre measures 2.5 m (8 ft.) in diameter, and is an estimated 12.6 metric tonnes (14 tons). This is as much as eight sports cars! It was discovered in 1966 by workmen trenching a new storm sewer in town, at a depth of 3.5 m (11.5 ft.)- possibly where it was originally formed. It was raised and placed on display at the town offices.
The Kettle Hills have been, and continue to be, used by local First Nations people for traditional resource harvesting-hunting, trapping, and gathering berries and plants for food and ceremonial use. Kettle stones themselves are considered to be sacred.
Sources:
http://www.manitobaparks.com/
Manitoba Geological Survey
To log this Earth Cache you must answer the following questions:Answers can be submitted by e-mailing the cache owner through their profile page. You may log the cache as found but your log will be deleted if we do not receive your answers within a few days.
1. Describe how kettle stones are formed.
2. How long ago was the origin of this particular concretion?.
3. How long ago was it transported to Swan River?
4. How was it transported to Swan River?
5. Approximately how tall is this kettle stone and how many paces does it take to get around it?
6. (Optional) Take a picture of yourself or your GPSr at the kettle stone.
We have earned GSA's highest level: