Interesting Facts

Growth Rate

The average growth is one cubic inch (per drip source) for every 100 years. This rate is influenced by several factors.

  • rainfall
  • weather patterns
  • ground acidity

Mystery Remains

Much is still unknown about the formation of cave speleothems. As scientific knowledge advances, present theories may need to be revised.

Cave Formations

Speleothems, commonly called formations, are mineral deposits formed by the evaporation of water that contains calcium carbonate. Marengo Cave exhibits a wide variety of formations.

Stalactites and soda stras

Stalactites, the most common of all cave formations, begin as soda straws. Soda straws form when slow seeping water enters through a cave's ceiling. The carbon dioxide gas in the water is released into the air and a tiny, circular ring of calcite (crystalized form of calcium carbonate) is left behind on the ceiling. Ring after ring of calcite is deposited until a hollow tube, the soda straw, is formed. These fragile formations can grow up to ten feet in length and sometimes break from their own weight. They can be seen in many sections of Marengo Cave.

If the central canal of a soda straw becomes plugged by deposition, the water begins to flow down its outside surface. This results in the calcite being deposited on the surface near the top. The soda straw gradually transforms into a cone shaped stalactite. These formations can become very large and are commonly found throughout Marengo Cave.

Stalagmites

Stalagmites are formed by water dripping from the cave ceiling or from a stalactite. If the water droplets retain some of their carbon dioxide, the gas will be released when the drops hit. The calcite is then deposited on the cave floor. Slowly a stalagmite begins to grow upward. They are usually larger in diameter than stalactites and are more rounded on top. Marengo Cave is noted for its slender Totem Pole stalagmites. Sometimes a stalactite and a stalagmite will meet and form a column.

Flowstone

Flowstone is formed when water entering the cave flows down walls or over floors and breakdown. This results in the deposition of successive layers or sheets of calcite. Mineral impurities in the water can add a variety of colors to flowstone formations. Flowstone is abundant in Marengo Cave.

Draperies

If the water entering a cave flows down a sloping ceiling, it will deposit calcite in thin, translucent sheets that hang in delicate folds like draperies.

Rim Stone Dams

Rimstone dams are formed as water flows and tumbles over an edge, like water overflowing a sink. The agitation causes carbon dioxide to be released. This, in turn, results in calcite being deposited out of solution around the tip of the dam. As the dam grows taller, it is capable of impounding more water. Rimstone dams are commonly found in many parts of Marengo Cave.

Helictites

Helictites are small, twisted formations that project from cave ceilings, walls, and even the floor. They appear to defy the laws of gravity. It is believed that they are formed when seeping water moves through a tiny central canal under hydrostatic pressure. Because of the small flow of water and other factors, the calcite is deposited irregularly. This causes the helictites to grow erratically--into weird, twisted shapes.

Cave popcorn

Another common cave formation is cave popcorn (also called cave coral). This formation can be found in many sizes, shapes, and colors. Most common, however, are the small, knobby clusters that resemble popcorn. Sometimes it forms knobs or branching stems which can extend several inches from the walls or floors. Cave Popcorn is unusual in that it can be deposited above or below water.