The terrain in Icelandic Fissures and the rock arch in Further Down the Coast use Voronoi patterns to mimic cracks far more realistically than Vue's built-in crack patterns (eg Sparse Cracks).
To experiment with this you need a version of Vue that gives you access to the Function Editor (eg any version above Esprit... or Pioneer + the appropriate upgrade package).
Take a Simple Fractal and change the Noise Type from default Perlin to Cellular -> Voronoi (not Voronoi Altitude or Generalised).
Edit the noise parameters and set Profile to "Spike" and Neighbour to one of the "x - y" types. "1st - 2nd" produces cracks less busy and complex than "3rd - 4th" with "2nd - 3rd" in-between.
Add an Opposite filter to the output.
Add a Smooth Clip filter to that and edit the Brightness and Contrast parameters (with the Function Node Preview window open so you can see what you're doing) such that just fissures show through the clipping threshold in V shapes. Brightness and Contrast should be