This volcano was built by Brandon Griffith and I for the Sarah Connor Chronicles. The core is a click hinge octagon. Then we made cascading triangles using (4) sides as "active" and the other (4) as "passive". Next we reversed the active and passive sides. If you look at a mountain you can see the same type of pattern. Last we mucked it up a bit to make a more organic texture.
Here's the video clip (Thanks Remi): www.youtube.com/watch?v=XaFLU_FItM4
As an aside, we were told to make a "Gilligan's Island" volcano. We needed it to read as Lego while on camera. It is on screen for about 2 min right at the start of Season 2, Episode 20(I hope). I couldn't find the clip on Hulu.