Spelunking: Exploring Caves and Caverns Michele Lomano Hedgesville Elementary School A cave or cavern is a natural opening in the ground that extends beyond the zone of light. Caves can occur in various rock types, but one rock type forms the most numerous caves—limestone. Limestone is composed of the mineral calcite (CakCO3). Most caves are formed by moving acidic water. Carbonic acid (H2CO3), produced when carbon dioxide (CO2) combines with water, dissolves limestones. This acid begins to move slowly in small fractures in the limestone. This process may continue for thousands of years as the cracks become holes, and the holes become rooms, forming caves. While this dissolving process continues, another process may occur—deposition. Stalagmites, stalactites, columns, and flowstone are formed in the reverse way of that by which the cave itself forms. The formations occur when the mineral calcite, which dissolves from the rock as the cave is forming, is deposited. The dripping or seeping of the calcite-rich water determines the shape of the formation. When the water evaporates, the CO2 leaves and only the calcite is deposited. Most formations are estimated to grow only one cubic inch per 120 years. A cave or cavern is a natural opening in the ground that extends beyond the zone of light. Caves can occur in various rock types, but one rock type forms the most numerous caves—limestone. Limestone is composed of the mineral calcite (CakCO3). Most caves are formed by moving acidic water. Carbonic acid (H2CO3), produced when carbon dioxide (CO2) combines with water, dissolves limestones. This acid begins to move slowly in small fractures in the limestone. This process may continue for thousands of years as the cracks become holes, and the holes become rooms, forming caves. While this dissolving process continues, another process may occur—deposition. Stalagmites, stalactites, columns, and flowstone are formed in the reverse way of that by which the cave itself forms. The formations occur when the mineral calcite, which dissolves from the rock as the cave is forming, is deposited. The dripping or seeping of the calcite-rich water determines the shape of the formation. When the water evaporates, the CO2 leaves and only the calcite is deposited. Most formations are estimated to grow only one cubic inch per 120 years. 1.Hypothesize which rock type best forms caves. Record hypothesis. 2.Label each beaker with the following: a.Sandstone w/water b.Shale w/water c.Limestone w/water d.Sandstone w/acid e.Shale w/acid f.Limestone w/acid 3.Using the triple-beam balance, measure the mass of each rock piece and record the data. Place each piece in the beaker labeled with its rock type. 4.Pour 50 ml (or enough to cover rock sample) of water in beakers a, b, and c. Pour 50 ml of diluted hydrochloric acid (or enough to cover rock sample) in beaker d, e, and f. 5.Let the beaker stand undisturbed for 20 minutes. Starting with the rock in beaker a, CAREFULLY and THOROUGHLY rinse the rock, being careful to avoid contact with the skin. Remove the rock, dry, then measure the mass of the rock. Record the results. Repeat this process for rocks b-f. 1.Hypothesize which rock type best forms caves. Record hypothesis. 2.Label each beaker with the following: a.Sandstone w/water b.Shale w/water c.Limestone w/water d.Sandstone w/acid e.Shale w/acid f.Limestone w/acid 3.Using the triple-beam balance, measure the mass of each rock piece and record the data. Place each piece in the beaker labeled with its rock type. 4.Pour 50 ml (or enough to cover rock sample) of water in beakers a, b, and c. Pour 50 ml of diluted hydrochloric acid (or enough to cover rock sample) in beaker d, e, and f. 5.Let the beaker stand undisturbed for 20 minutes. Starting with the rock in beaker a, CAREFULLY and THOROUGHLY rinse the rock, being careful to avoid contact with the skin. Remove the rock, dry, then measure the mass of the rock. Record the results. Repeat this process for rocks b-f. Determine which rock type best forms caves. One 40-minute class period or one prior day setup and next day activity 1.In which beakers did change occur in the rock mass? In which beakers did no change occur? 2.Which rock type lost the most mass? 3.Why do you feel change occurred in some rock but not in others? 4.At the rate at which the rock in question 3 was dissolving, how long would it take to completely dissolve? 5.Compare and contrast the cave forming abilities of the rock types you have tested. 1.In which beakers did change occur in the rock mass? In which beakers did no change occur? 2.Which rock type lost the most mass? 3.Why do you feel change occurred in some rock but not in others? 4.At the rate at which the rock in question 3 was dissolving, how long would it take to completely dissolve? 5.Compare and contrast the cave forming abilities of the rock types you have tested. Student data is clear and reasonable Students properly relate the formation of a cave in limestone to chemical weathering Students use observed results to successfully determine the effects of acid on various rock types and devise a way of positively identifying limestones in the field Student data is clear and reasonable Students properly relate the formation of a cave in limestone to chemical weathering Students use observed results to successfully determine the effects of acid on various rock types and devise a way of positively identifying limestones in the field For each group of students: 6 small beakers or baby food jars Diluted hydrocloric acid (5%-10%) Triple-beam balance Grease pencil or masking tape 2 similar-sized pieces (hand specimen size) each of sandstone, shale, and limestone Paper towels For each group of students: 6 small beakers or baby food jars Diluted hydrocloric acid (5%-10%) Triple-beam balance Grease pencil or masking tape 2 similar-sized pieces (hand specimen size) each of sandstone, shale, and limestone Paper towels SAFETY NOTE: When using hydrochloric acid, follow all lab safety measures. None listed Objective Materials and Equipment Materials and Equipment Time Procedures Assessment Overview Questions Teaching Suggestions Safety Note