Pozzo del Merro is a flooded

sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water ...

in the countryside northeast of

Rome Rome (Italian language, Italian and , ) is the capital city and most populated (municipality) of Italy. It is also the administrative centre of the Lazio Regions of Italy, region and of the Metropolitan City of Rome. A special named with 2, ...

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

. Situated at the bottom of an 80 m conical pit, at it is the second deepest underwater vertical cave in the world. In 2000 two ROVs were sent to explore its depths; the first, the "Mercurio (Mercury)" reached its maximum operative depth of without reaching the bottom. The second ROV, "Hyball 300", reached without touching down either. A third dive in 2002 with the more advanced "Prometeo" robot reached the bottom at , but discovered a narrow passage continuing horizontally. The sinkhole, similar to the Zacatón cenote, was formed by volcanic activity eroding the

carbonate rock Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and Dolomite (rock), dolomite rock (also kn ...

. The sinkhole is part of the natural reserve Macchia di Gattaceca e Macchia del Barco (created in 1997).

References

Sinkholes of Italy Metropolitan City of Rome Capital {{geology-stub