How is an airplane seeing a top down view of the "bottom" of a glacier river? Is the glacier river suspended high in the sky above? Is the airplane a transformer that can also go through the sea like a submarine? If it was the latter case, it wouldn't be a top-down view though, unless you're saying top down view from the perspective of the Submarine being perhaps upside-down underwater and looking "down" to the bottom of the glacier river.

Assuming this means "view of the top of a glacier river as seen from an airplane," but with the wording I can't be so sure. Perhaps it means that this is the "bottom" of a glacier river in the sense of it being at the lowest elevation, so perhaps it is just a part of the glacier river seen from above but only showing us a portion of the "end" of said river.

Whatever, probably confusing people more with my concerns than the title ever did.