LoansumLdy, ScubaLdy, Amanda: RE Sinkholes
Ambergris Caye in underlain by Pleistocene limestone just like most of Florida. The limestone is the remnants of reef that was deposited when sea level was much higher than today. During the last glaciation (ended about 15,000 years ago)sea level was much lower than today (all the water went to making ice in Canada). Rainfall at that time percolated thru the limestone to make significant caves (including the Blue hole). When the glaciation ended and sea level rose, the caves were flooded. When a cave roof collapses it creates a sinkhole. Earthquakes help with the collapse process. The whole process is very common whereever you have limestone, rain and construction. Places like Florida have geophysical surveys which will tell you if you have potential problems before you build. If you go to google earth on the mainland, sinkholes are black dots of water about 50-100m wide.
Hope this helps