The grikes of Tsingy de Bemaraha

This is a very cool graphic from National Geographic showing how these most unusual rock formations of western Madagascar formed (carved by groundwater erosion, not by precipitation).

I've embedded a smaller gif to save my bandwidth; those interested in the process can read the details in this larger version.

(I'll bet when you woke up this morning you didn't even know what a grike was.  Neither did I.)

Via Geology Rocks.

A tip of the hat to Randomscrub, who notes that Titan also has karst topography!