It's a air pocket
Boat cannot move or circulate. bg
The first chapter in the book "Flipped" by Wendelin Van Draanen is called "The Very Beginning."
A temperature inversion.
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hid it under a pile of brush
When it is under sail!
Yes. But only for a short time.
To securely fasten your canoe to a roof rack using canoe straps, follow these steps: Place the canoe upside down on the roof rack. Loop the straps under the crossbars of the roof rack and over the canoe. Pull the straps tight and secure them by fastening the buckles. Make sure the canoe is centered and secure before driving.
Generally, gas is trapped in a container, or under a curved surface.
I watched a terrapin swin slowly under the canoe
drowning?
No. Dissolved gasses trapped under pressure provide the force.