It's an imaginary fear and a respect for the power of nature. These effects are greater than real in the sense that the painting is two dimensional, and yet it evokes the feelings of a real event. The effects are less than real because one knows there is no real danger as there would be in the actual depicted event.
Walton's "propaE theory makes a lot of sense to me and his example of the shipwreck is a valid one. Paintings and other artistic expressions are tools to spur the imagination into entering the piece and finding meaning there. Using the same shipwreck painting as an example, one could wonder, "Are they going to surviveaE This in turn induces more questions and scenarios such as if there are any other ships around that can save the shipwrecked people, where they are and are they close enough to land to have some hope of survival, etc. Those questions would be literal ones. Another might see the ship as a metaphor for the struggles of life ending in the inevitable decline of the vessel we steer on the sea of our l