posted on May, 2 2008 @ 10:24 AM
reply to post by mrimmense
Thats called a volcano
Such things are impossible to occur without catastrophic events, as mentioned earlier, a meteor strike for example.
The crust is massively thick (compared to humans I mean, on an earth scale, its thin). However, the supporting mantle is many times thicker. It is
impossible for enough mantle to be displaced by normal means to allow for large regions to fall in that far. It is possible however, to have
supporting caves, hollowed out regions, and the stress of an event to cause regional sink-holes on a large scale. However for it to be, say, even
city-sized sink hole, special circumstances need to exist.
As for how ocean floors are formed... those plates on the ocean floor are somewhat newer (not in all regions) and thinner. Theres two directions for
crust. Up or Down. The subduction zones, the ocean crust is slowly pushed under the continental crust, and turned back into magma. Elsewhere, crust is
pushed upwards, forming new lands and mountain ranges. Ocean floors are simply a lower-area of Earth, not where sink holes have occurred to create