It's wild in the upper midwest you can SEE the glacial effects on the terrain better than any topo map I've seen before.

I was wondering that too, that this might be a better visualisation of certain geological features. But I don't have much experience, so can't say for sure.

It's a sort of high-pass filter I guess? Using the curvature of the earth to highlight local changes in elevation.

I'm not that familiar with high-pass filters. But yes it's the way it exposes local changes in elevation that is unique. Indeed the heatmap is generated dynamically for every change to the zoom and viewport.