Grotto Guide Orientaton Course

What is the Grotto?

Your students and customers will want you to be able to answer their questions about the Grotto. Is it a rock quarry? Did it occur naturally? How long has it been here? You will need to be able to tell them.

4 In geologic terms, what exactly is 40 Fathom Grotto?.

The Grotto is what geologists refer to as an in-line sinkhole. It formed centuries ago when the earth collapsed above an underground river.


North-central Florida has surprisingly few surface rivers and streams. Most water flows under ground, through a series of natural underground caves.

When these caves pass beneath an area of geologic instability, it is not unusual for the rock above them to collapse, forming domes on the cave ceiling, and debris cones on the floor beneath them.

In time, many of these domes collapse completely, forming open sinkholes. In areas where high populations cause rapid drops in the water table, sinkholes can form rapidly, with little warning. In general, however, sinkhole formation is a process that takes hundreds — or even thousands — of years.

No one is certain when the Grotto first opened a window to the Floridan Aquifer. There is no record of it having formed after Europeans first came to Florida.

Today, the underground river originally responsible for the formation of the Grotto no longer flows. This is why there is little or no detectable current in the Grotto,

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