Student Activities

Creating a Cave Part 3: Dissolution

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Grade Level:
Upper Elementary: Third Grade through Fifth Grade
Subject:
Science

Background

Students will learn how caves are formed, the geologic processes involved, and the major types of caves. They will experience how the geologic process of dissolution, combines with infiltration by making a cave or karst model.

Teacher Information

Living in an area with soluble bedrock presents a number of unique problems. As caves form near the surface, the ceiling often collapses into them, creating sinkholes. A region in which the landscape contains cave entrances, sinkholes, sinking streams, and springs flowing from holes in the ground is called karst Roadways and houses have been swallowed by sinkholes in Kentucky and Florida. In these areas, caves are usually the primary storm drain system. If rainfall amounts exceed the amount of water the cave can process, or if a collapse has blocked some of a cave passage, water can back up in the system, causing flooding in sinkholes. Houses and buildings near these sinkholes can be flooded, even if they are miles from the nearest river. An even bigger problem is that of groundwater pollution. It is estimated that 25% of the world's population obtains its water from karst aquifers. Typically, in non-karst aquifers, impurities are filtered out as water infiltrates and makes its way down to the aquifer. In a karst aquifer, the routes from the surface to the aquifer are quite direct, allowing for very little filtration.

Runoff from parking lots, feedlots, and dumps often feeds directly into cave systems. Most of the karst aquifers in the US are threatened due to pollution and development on the surface.

Caves are formed in various ways:

  • Solutional caves are formed by weak, natural acid dissolving soluble rocks such as limestone, dolomite, gypsum and marble. Timpanogos is a solutional cave made mostly of limestone, as are 95% of caves.
  • Lava tubes form during the cooling of lava flows. First, a crust forms on the lava as it begins to cool. Molten lava that is under the crust continues to move with the volumes of hot lava slowly receding, making tunnel-like passages.
  • Sea caves form from wave action. The waves force water into the cracks in rock, breaking off the rock.
  • Wind caves form from wind erosion or cliffs or hills. They are almost always small caves that seldom penetrate into total darkness.
  • Talus caves form from huge rocks that have fallen from cliffs.
  • Glacier caves form by melting ice  water moving through glaciers.
  • Soil caves form when flash floods move through the soils and transport earth with them. They are found in desert areas.
  • Tectonic caves form by the action of earthquakes.

Materials

square or rectangular baking pan, sugar cubes (enough to cover at least one layer in the bottom of the pan), warm water, food coloring, eye dropper, thin layer of plastic or plastic wrap, photos of various types of caves

Procedure

1. Discuss the various processes of cave formation with the students (see Teacher Information) Have the students compare and contrast the various types of caves shown in the photos.

2. Make a cave or karst model:

a)     Place the sugar cubes in at least one layer in the bottom of the baking pan. These represent the more permeable rock, like limestone. 

b)     Lift one edge of the pan to give it a gentle slope. The pan represents an impermeable lower layer of rock.

c)      Mix warm water with a few drops of food coloring for contrast. Select a point near the upper end of the sugar cubes to begin dripping the water mixture. The colored water represents the carbonic acid in the ground water. Observe how the "limestone" begins to dissolve and form caves. 

d)     Now cover the sugar cubes completely with the plastic, placing about a quarter inch hole in the center near the lower end of the baking pan. This represents an impermeable layer of rock over the limestone with a small crack or fault in it. 

e)     Begin dripping the water mixture in the same place as before. Observe how the water travels over the surface until it reaches the hole or crack, then begins dissolving a cave underneath it. Lift the plastic to view the new cave formed under the surface.  The results are best observed immediately following the experiment. As the water sets, all the sugar cubes eventually dissolve.

3. Discuss what could happen to the earth's surface if the cave below became big enough. Introduce the idea of sinkholes and karst valleys. Ask students what problems face those who live in areas where there are active caves. Introduce the danger of cave-ins when exploring caves.

Extensions

·        Students could make their own cave or karst model in small groups.

·        Students could make a pre and post experiment chart with hypotheses and observations.

·        Powerpoints on Timpanogos Cave at https://www.nps.gov/tica/forteachers/classroom-packet.htm

·        http://www.pbs.org/wgbh/nova/earth/how-caves-form.html animated story of different types of caves.

Additional Resources

https://www.nps.gov/cave/forteachers/ms_geology.htm Carlsbad Caverns National Park, Hangy Downys, Sticky Upys and Other Pretty Cave Decorations, A River Runs Through it…Literally!

http://www.kidsdiscover.com/blog/spotlight/caves-for-kids/ photo of a lava cave, sea cave, and Mammoth (Solutional) cave.

http://www.adventure-caves-usa.com/cave_types.html photos and descriptions of various types of caves including glacier/ice caves.

Last updated: October 23, 2015