4 ms·

If it's rift due to plate separation, wouldn't the crack go down all the way to the mantle? Not the 20-30 feet seen in the video.

• lisper 9y ago
  It does, but in general when a rupture opens up at the surface, the side walls fail quickly and fill it in with loose material. It is only when a surface rupture is "fresh" that it looks as dramatic as this.
  • hyperpallium 9y ago
    Sure, the side walls fall in... but wouldn't that happen more easily near the surface, with loose topsoil, than for deeper rock? Meaning, that if the top part hadn't fallen in yet, the lower parts wouldn't have either. Perhaps pressure with depth is a factor, tending to press the sides together. Amd the deeper material might not be rock, but e.g. sand or other loose material.
    • lisper 9y ago
      There isn't just one well-defined crack. Where the plates are separating there is a whole zone of material that is being pulled apart and cracking open. The current crack is just one of many many fissures in the rift zone. And the individual fissures are jagged and ziggy-zaggy, so even if they had clean sidewalls you still couldn't see straight down to the bottom. Also, the crack is not filled in all the way to (near) the top. There are gaps and voids all the way down. The "bottom" that you see is just the first filled-in part. If you dug down you'd probably find more gaps. (I'm not 100% sure about this. I know about the mechanics of slip-strike faults because I live in California within walking distance of the San Andreas, but the African rift is different so I could be wrong about some of these details.)