A metamorphosis is a transformation. In this image, a model, also shown in Nude Descending a Ladder, is transforming into a portion of Multnomah Falls (or vice versa, the waterfall is transforming into the model). More abstractly, there is a larger view in which the waterfall is itself becoming a figure—vengeful Goddess or otherwise!
The two images I combined to make Metamorphosis are Waterfall (below) and Shout to the Soul (far below). Waterfall is a fairly straight photo of a portion of the upper Multnomah waterfall, while Shout to the Soul has been manipulated and transformed to fit together with the falling water.