Chapter – 10 Section 10.2 – Groundwater Weathering & Deposition

1. Chapter – 10Section 10.2 – Groundwater Weathering & Deposition

2. Section 10.2 Section – 10.2 Objectives • Explain how groundwater dissolves and deposits rocks and minerals. • Illustratehow caves form. • Describehow the features of karst topography shape the landscape.

3. Section 10.2 Chemical weathering of limestone by water causes the characteristic topography of karst areas. Review Vocabulary hydrolysis: chemical reaction of water with other substances

4. New Vocabulary Cave Sinkhole Karst Topography Stalacite Stalagmite

5. Section 10.2 Carbonic Acid Most groundwater is slightly acidic due to carbonic acid. Carbonic acid forms when carbon dioxide gas dissolves in water and combines with water molecules.

6. Section 10.2 Dissolution by Groundwater The process by which carbonic acid forms and dissolves calcite can be described by three simple chemical reactions. In the first reaction, carbon dioxide (CO2) and water (H2O) combine to form carbonic acid (H2 CO3 )

7. Section 10.2 Dissolution by Groundwater In the second reaction, carbonic acid splits (decomposes) into hydrogen ions (H+) and bicarbonate ions (HCO3–)

8. Section 10.2 Dissolution by Groundwater In the third reaction, the hydrogen ions (H+) react with calcite (CaCO3) and form calcium ions (Ca2+) and bicarbonate ions (HCO3–).

9. Section 10.2 Dissolution by Groundwater - Caves The processes of dissolving, called dissolution, and precipitation of calcite both play a major role in the formation of limestone caves. Caves - A natural underground opening with a connection to Earth’s surface is called a cave or cavern.

10. Section 10.2 Dissolution by Groundwater Caves As groundwater infiltrates the cracks and joints of limestone formations, it gradually dissolves the adjacent rock and enlarges these passages to form an interconnected network of openings.

11. Section 10.2 Dissolution by Groundwater Karst topography A sinkhole is a depression in the ground caused by the collapse of a cave or by the direct dissolution of limestone by acidic water. Limestone regions that have sinkholes and disappearing streams are said to have karst topography.

12. Section 10.2 Groundwater Deposits Dripstones Dripstones are rock formations that are built over time as water drips through caves. Each drop of water hanging on the ceiling of a cave loses some carbon dioxide and precipitates some calcite.

13. Section 10.2 Groundwater Deposits Groundwater Weathering and Deposition Dripstones A form of dripstone, called a stalactite, hangs from the cave’s ceiling like icicles and forms gradually. As the water drips to the floor of the cave, it may also slowly build mound-shaped dripstones called stalagmites.

14. Section 10.2 Groundwater Deposits Hard water Water that contains high concentrations of calcium, magnesium, or iron is called hard water. Hard water is common in areas where the subsurface rock is limestone. Calcite present in limestone can be precipitated in water pipes, which in turn can cause problems on the heating elements of the household appliances.

15. Summary Chemical weathering of limestone by water causes the characteristic topography of karst areas. Groundwater dissolves limestone and forms underground caves. Sinkholes form at Earth’s surface when bedrock is dissolved or when caves collapse. Irregular topography caused by groundwater dissolution is called karst topography. The precipitation of dissolved calcite forms stalacite and stalagmites in caves. Deposits of calcite in hard water can clog water pipes and render electrical appliances useless.