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How Kettle Holes are Formed
A) Kettle holes are Fluvioglacial landforms which are formed when ice that calves off of glaciers become becomes covered by sediment in the outwash plain. Fluvioglacial landforms are those that are formed by glacial meltwater. Glacial outwash is generated when streams of meltwater flow away from the glacier and deposit sediment to form broad outwash plains called sandurs.
B) Kettle holes can also form as the result of floods caused by the sudden drainage of an ice-dammed lake. These floods, called jökulhlaups, often rapidly deposit large quantities of sediment onto the sandur surface. The kettle holes are formed by the melting blocks of sediment-rich ice that were transported and consequently buried by the jökulhlaups. Ramparts may form around the edge of kettle holes generated by jökulhlaups. The hole itself is formed when the ice melts.
What Happens to Kettle Holes
Over thousands of years, peat moss progressively filled in the kettle holes from the edges inward toward the pond centers. Most kettle holes still have a central bog pond with a floating mat/moss border, while some have filled the kettles entirely with peat, obscuring the former ponds under floating or grounded peat mats.
A kettle bog occurs when little water other than rainwater enters the area. A kettle lake occurs when the area has a source of new water to replenish what is there.
This Kettle Hole
The Ponemah Bog Wildlife Sanctuary features a three-acre pond surrounded by a floating sphagnum mat and encircled by upland oak-pine woods. The three-acre pond is all that remains of the ancient 100-acre lake. This bog resulted from the last receding glacier, which left a kettle hole pond in the Souhegan River outwash plain. Changes over the last 12,000 years have been recorded by the bog itself, which has preserved, in its layers of peat, pollen blown in from the surrounding woods. The moss mat has advanced over the last 6000 years to gradually fill in the pond with plant remains.
The food web is rather simple in bogs: the acid peat locks up most of the nutrients, offering little to support grazing animals and their predators.
The Ponemah Bog Wildlife Sanctuary is managed by the NH Audubon Society. Please stay on the trails and the boardwalk to protect the sensitive environment. Dogs are not allowed in the wildlife sanctuary. Reading the material linked to at the end of this description will provide you with more background on the type of plants, including insect eating plants, and trees that can be found in the area. I'd encourage you to visit all four of the viewing platforms, three next to the bog and the overlook platform.
Logging Requirements (don't post in your log but email me):
To log this earthcache, message or email us and copy and paste these questions, along with your answers. Please do not post the answers in your log, even if encrypted. There's no need to wait for confirmation from us before you log, but we will email you back if you include your email address in the message. Group answers are fine; just let us know who was with you.
- Do you think that this kettle hole was caused by a jökulhlaup? Why or why not?
- Estimate how tall the trees are at the GZ coordinates? What do you think might explain their height based on your observations and the information on this page?
- What locks up the nutrients in a kettle bog?
- For how long as this bog been filling up with plant remains?
Descriptions from the NH Audubon Ponemah Bog Wildlife Sanctuary guide, NH Natural Heritage Bureau as well as Wikipedia.
Congrats to britpitts, ChcknLdy, and Team Skywalker on their FTF!