posted on Mar, 23 2011 @ 10:55 PM
reply to post by stirling
Could be one of many things Stirling.
*Limestone errosion (Most comin) basically water erodes limestone very quickly which is how 80% of the worlds caves are formed.
*Underground River taking the soil away,
*Airpocket that after thousands of years has lost its stability due to recent environmental factors be it Bulldozing, Earthquakes, Drilling even and
espeacially drifting of the techtonic plates
*Oil being taken out of the ground leaving and empty hole
*An old lava tunnel colapsing kilometers underground
Pritty much anything can cause this.
Oh and let us not forget ALIENS... they could have done it too