in fact many cities are said to be built over huge empty
caverns.
supposedly, there are huge extensive underground tunnels deep
under New York City !
in any case, i don't buy the sewage fluid dissolving the rock
story because then the whole city block would have collapsed too
and not just a single house !
It is possible as you might not experience here in SG....but the
soil acidity level can be quite high especially on
Volcano land.
But a 30 stories sinkhole is by far the biggerest
and typically the Sinkhole in N.A doesn't cut this
straight it look like a dent that looks like a crater slop inward.
But the picture here is a Vertical Nicely smooth Cut.
