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This is a massive sinkhole that was created when a gypsum stack collapsed in Florida. Gypsum stacks are byproducts of phosphate mining processes. Say the researchers:
This massive sinkhole formed on top of a gypsum stack in Florida, and contributed to contamination of the aquifer below. Grouting work by Hayward Baker to seal the aquifer from the gypsum stack was recognized with a national award.
