Cavern Geology Lesson Plan 3: Types of Speleothems


Students will learn to identify several types of speleothems that are commonly found in limestone caverns.

Background Information

Continuing with the limestone cavern example, the terminology used in this lesson will reflect this cavern type. However, the names of speleothems are defined by their shape regardless of the material they are created from.

As mentioned in Lesson 2, formations begin when calcium bicarbonate enters the cavern and the chemical balance of the solution alters, forcing the calcium carbonate to deposit on the surface of the cavern ceiling or wall it entered through. The path of the watery solution from there is what determines the shape of the eventual speleothem as it deposits calcite along the way.

Listed below are some of the most common forms of speleothems and a brief description of how each is created. There are several other speleothem formations found in caverns around the world. Some are very rare, found only in unusual conditions.

Soda Straw – Formed when the solution first enters the cave from the ceiling and the calcite crystallizes around the drop forming a ring before the drop falls. As drop after drop continues to enter the cave at the same point, the water will then travel through the rings deposited before them, building ring upon ring at the end of the last one. Over time, the result is a thin, hollow tube that resembles a straw.

Stalactite – When a soda straw is forming, the solution will also deposit calcite along the inside of the tube as it travels through it. Eventually, the straw will become solid. At that point, as the solution continues to want to enter the cave at the same point, it is forced to the side of the tube, then runs down the outside. Over time, the result looks like an icicle.
Stalagmite – As the watery solution falls from the ceiling, it lands on the floor or a ledge where it splashes or runs over an area, leaving the remaining calcite in its wake. The continued deposits build into a mound.

Note: while a stalactite and a stalagmite are formed from the same drops of water, the nature of their growth means that a stalactite may possibly grow in length faster than a stalagmite will grow in height. However, the stalagmite will most likely be wider than the stalactite. There are two easy ways to help your students remember the difference between a stalactite and stalagmite:
Stalactite is spelled with a C for ceiling
Stalagmite is spelled with a G for ground

A stalactite holds “tite” to the ceiling
A stalagmite “mite” reach the ceiling someday
Column – Usually a stalagmite is directly below a stalactite. Over much time they may finally meet. As calcite continues to run down the length of the stalactite, it now continues to run down the connected stalagmite smoothing the connection point. Some columns have been together for so long it is hard to tell where the two formations first joined.

Flowstone – Similar to the formation of a stalagmite. However, the area receiving the deposit has a slope to it, so the water runs down the slope in a wide spread. A flowstone can cover a large area.

Drapery/ bacon strip – When a water drop emerges on a vertical wall, gravity drags it down the side of the wall depositing calcite in a line. Each additional deposit builds up this fine line until it looks like hanging material. Draperies with red hues, caused by iron and other minerals in the calcite solution, look like bacon strips.

Rimstone Dam – (also known as Gours in Europe) Depressions in the cave floor may collect saturated water. The calcium in the solution will deposit around the edge of the pool. Eventually the deposits build up so high that more and more water can be held. The calcite deposits act as a dam.

Cave Pearl – (also known as Oolites) If a pebble is in a rimstone pool, the saturated water will coat it. As water drops continue to fall in the pool, they cause ripples which gently roll the pebble, giving it a smooth coating.

Experiments & Activities

Grades K – 4 “Create a Cavern”

Build a cavern bulletin board or diorama. Students can cut and paste, draw pictures, or create three dimensional artwork.

Students may also create a classroom cavern. (This is done by draping three sides of a table with a dark cloth or using a large box) Suggestions include: narrow tubes (paper towel holders) for soda straws, cones for stalactites and stalagmites, crumpled balls of paper to “build” flowstone. Glue or tape the formations into the display.

Grades K – 4 “Memory Game”

Make two copies of the speleothem pictures form (included with the worksheets).

Paste onto construction paper or cardboard and cut into cards.
Play the memory game – lay the cards upside down on a table in no particular order.

Students take turns turning over two cards. When they match two identical cards, they remove them. They player with the most matches wins.

Grades K – 4 “Flash Cards”

Make one copy of the speleothem pictures form (included with the worksheets).

Paste onto construction paper or cardboard and cut into cards.
Write name of formation on back of cards.
Use as flashcards.

Grades 5 – 8 “Speleothem Identification Activity 1”

Match drawings of formations with their names using the “Speleothem Match” worksheet included.

Grades 5 – 8 “Speleothem Identification Activity 2”

Draw a cave using at least 5 of the formations using the “Draw a Cavern” worksheet included.

Grades 9 – 12 “Speleothem Research”

Besides the speleothems covered in this lesson plan, there are several other varieties, including helictites, cave coral/popcorn, shields, aragonite flowers and false floors. Students can research these different types and how they grow.