Stalactites, Stalagmites, and Cave Formations

 

A special sight in any cave are the strange and one-of-a-kind formations known as speleothems!

Some places within the Mammoth Cave abound in wonderful formations not to be missed. In wetter areas these may be calcite formations like stalactites and stalagmites. In drier areas the cave formations may display as gypsum flowers and “snowballs”.

Learn about many of our formations, as well as where in the cave you can see them below.

 

These broken cave formations, near the Frozen Niagara section of Mammoth Cave, may take centuries to regrow.

NPS Photo/ Rachel Kem

Fragile and Slow

Both the calcite and gypsum formations in Mammoth Cave took thousands of years to form. In addition, many formations are incredibly fragile and can break or be forever damaged by a simple touch of the hand. Some of the park caves have been looted of their formations by past visitors looking to sell them for a profit. This destruction has forever robbed us of seeing these sections of cave in their full beauty as the damage cannot be reversed within our lifetimes.

We encourage all people who visit the park to be respectful of the caves irreplaceable treasures and remember to not touch cave walls or formations. They may break very easily and even the oil from your hands can cause them to stop growing.

 

Stalagmites, stalagmites and columns inside Violet City of Mammoth Cave.

NPS Photo/ Jackie Wheet

Stalagmites, Stalactites and Columns

Stalagmites and stalactites are some of the best known cave formations. They are icicle-shaped deposits that form when water dissolves overlying limestone then re-deposits calcium carbonate along the ceilings or floors of underlying caves.

Stalactites form along ceilings and hang downward. You can remember this with the phrase “Stalactites hang TIGHT to the ceiling.”

When stalactites are actively forming, they drip water. Where that water hits the floor, a mound-shaped stalagmite will form. You can remember this with the phrase “Stalagmites push up with all of their MIGHT.”

If stalactites and stalagmites continue to form and eventually meet, a column will form. This creates a decorative post that reaches from floor to ceiling. This looks just like a “column” you might see on a building.

Popular places to see stalactites, stalagmites, and columns in Mammoth Cave include: the Frozen Niagara room as seen on the Frozen Niagara tour and the Domes and Dripstones tour; the entrance room of the Great Onyx lantern tour; on the Wondering Woods cave tour; and along the Gothic Avenue tour, where visitors see formations that once captivated Mammoth Cave’s first tourists in the early 1800s.

 

Other Calcite Formations

Depending on how water flows in a cave, many unique shapes and formations are possible.

 

The Frozen Niagara is one of the most popular examples of flowstone in Mammoth Cave.

NPS Photo/ Deb Spillman

Flowstone

Flowstone refers to sheets of calcium carbonate that form along cave walls. Flowstone hangs downward and may create curtain-like sheaves along ledges, better known as draperies. The most notable flowstone formation in Mammoth Cave is the Frozen Niagara.

 

Helictites can form odd shaped formations pointing in many directions.

NPS Photo/ Deb Spillman

Helictites

Helictites form in cave areas with minimal water seepage. Because water does not drip off of the helictite, as would happen with a stalactite, the water coats its surface creating strange, branch-like shapes. Helictites can be seen along the Great Onyx Lantern Tour.

 

The oddly shaped bumps on the cave surface can sometimes resemble popcorn, leading to its name.

NPS Photo/ Rachel Kem

Cave Popcorn

Cave Popcorn refers to knobs of calcite that form where water seeps through pores in limestone, creating clusters that resemble popcorn, peas, or grapes. Cave Popcorn can be seen along the Grand Avenue and Domes and Dripstone Tour.

 

The rimstone dams seen on the Frozen Niagara section transition between dry basins and overflowing dams.

NPS Photo/ Thomas DiGiovannangelo

Rimstone Dams

Rimstone dams form along floors where calcite rich water pool. These dams grow larger as more calcite is deposited and water continues to flow over the edge of the dam. Rimstone dams can be seen in the Frozen Niagara section.

 

Cave Minerals

Prehistoric American Indians utilized minerals from Mammoth Cave about 2000-3000 years ago. They came in and collected gypsum, epsomite, and mirabilite from the walls and sediments of the cave.

 

Delicate gypsum flowers decorate the New Discovery section of Mammoth Cave.

NPS Photo/ Thomas DiGiovannangelo

Gypsum

Gypsum is a mineral that forms in the dry areas of the cave. It is a calcium sulfate mineral that is soluble in water. It is most commonly seen as delicate white crystal found along tour routes such as Cleveland Avenue and Kentucky Avenue. Along Broadway in historic section of Mammoth Cave you can also see gypsum, but it is covered with a dark coating (so it looks dark brown instead of white).The coating on this gypsum is from smoke from the torches that people used in the cave 2000 – 3000 years ago. This discoloration can be seen particularly well near Giant’s Coffin and the historic Tuberculosis Huts. Gypsum will also grow as crystals in the dirt along some cave passages.

Types of Gypsum Formations

Crusts — Crusts are where gypsum lines the walls as thin (or sometimes thick) plate covering (actually extruding from) the limestone. Crusts are common along the Historic Tour, Grand Avenue, and Great Onyx routes.

Flowers — Gypsum may also grow outwards in shapes that resemble flowers. This occurs in areas such as Cleveland Avenue and Kentucky Avenue. Flowers, like crusts, form as the gypsum extrudes from the rock (like toothpaste from a tube). In a crust all the crystal grow at about the same speed, but to form a flower, some of the crystals grow faster than others.

Snowballs —This formation is the one that gives the Snowball Room its name. They are globular white gypsum balls that cover the ceiling.

 

Minerals like mirabilite can be found only in the driest of cave passages.

NPS Photo/ Mary Schubert

Mirabilite and Epsomite

Mirabilite and Epsomite are two other minerals that occur in dry sections of the cave. They can form in areas in the winter (when the air is drier) and dissolve away when more humid air comes in. They form a sprinkling on the floor that gives the Snow Room on the Lantern Tour its name.