Stalactites and stalagmites in Gruta da Lapinha, near Belo Horizonte, MG Brazil
Unless you are unfortunate enough to suffer from claustrophobia, you will be severely tempted by the idea of exploring cave systems, especially big ones, because they can contain some of the most spectacular rock formations you could ever wish to see. Stalactites and stalagmites are two types of such formations typically found in caves. Stalactites hang from the ceiling, much like icicles. Stalagmites, on the other hand, grow from the floor.
Image: Val Vannet
The Sword of Damocles, Ingleborough, UK, the largest stalactite in Britain
Stalactites and stalagmites are formed when minerals precipitate out of dripping water. The time frame for the formation of stalactites and stalagmites is a subject of dispute. Some believe they both take tens of thousands to millions of years to form. According to the creationist model, however, they are able to form much more quickly, and often do.
Image: Daniel Maver
Hall of Giants, Carlsbad Caves, New Mexico
In Sequoia Caverns, stalactites protected from tourists from 1977-1987 grew 10 inches, or 1 inch per year. At this rate they could have grown 300 ft in just 3600 years.