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7.10: Landforms from Groundwater Erosion and Deposition

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How would you find an undiscovered cave?

Caves may be beneath your feet, especially if your feet are on limestone. In 1974 two amateur cavers found warm, moist air coming out of a crack in the ground in southern Arizona. They managed to find a way in and discovered the amazing Kartchner Caverns, 2.5 miles of pristine caves. You can see these spectacular caverns on a guided tour.

Groundwater Erosion

Rainwater absorbs carbon dioxide (CO 2 ) as it falls. The CO 2 combines with water to form carbonic acid. The slightly acidic water sinks into the ground and moves through pore spaces in soil and cracks and fractures in rock. The flow of water underground is groundwater . Groundwater is described further in "Concept Water on Earth."

When water sinks into the ground, it becomes groundwater.

Groundwater is a strong erosional force, as it works to dissolve away solid rock ( Figure above ). Carbonic acid is especially good at dissolving the rock limestone.

Cave Formation

Working slowly over many years, groundwater travels along small cracks. The water dissolves and carries away the solid rock, gradually enlarging the cracks. Eventually, a cave may form ( Figure below ).

Water flows through Russell Cave National Monument in Alabama.

You can explore a fantastic cave, Kartchner Caverns, in Arizona, by watching this video: http://video.nationalgeographic.com/video/player/science/earth-sci/exploring-kartchner-sci.html .

Sinkholes

If the roof of a cave collapses, a sinkhole could form. Some sinkholes are large enough to swallow up a home or several homes in a neighborhood ( Figure below ).

A relatively small sinkhole in the United Kingdom.

Groundwater Deposition

Groundwater carries dissolved minerals in solution. The minerals may then be deposited, for example, as stalagmites or stalactites ( Figure below ). Stalactites form as calcium carbonate drips from the ceiling of a cave, forming beautiful icicle-like formations. The word stalactite has a c, and it forms from the ceiling. Stalagmites form as calcium carbonate drips from the ceiling to the floor of a cave and then grow upwards. The g in stalagmite means it forms on the ground.

Stalactites hang from the ceiling and stalagmites rise from the floor of Carlsbad Caverns in New Mexico. The large stalagmite on the right is almost tall enough to reach the ceiling (or a stalactite) and form a column.

If a stalactite and stalagmite join together, they form a column . One of the wonders of visiting a cave is to witness the beauty of these amazing and strangely captivating structures. Some of the largest, and most beautiful, natural crystals can be found in the Naica mine, in Mexico. These gypsum crystals were formed over thousands of years as groundwater, rich in calcium and sulfur flowed through an underground cave. Check it out:

Summary

  • Groundwater dissolves minerals, carries the ions in solution, and then deposits them.
  • Groundwater erodes rock beneath the ground surface, especially carbonate rock.
  • Groundwater deposits material in caves to create stalactites, stalagmites, and columns.

Practice

Use this resource to answer the questions that follow.

Kartchner Caverns State Park, Arizona

http://www.youtube.com/watch?v=uF75q4vzbAY

1. What is under Arizona?

2. When were they discovered?

3. When did this area become a state park?

4. How long did it take the caverns to form?

5. What makes caves interesting?

Review

1. How does groundwater erode rock material?

2. Describe how groundwater deposits stalactites and stalagmites.

3. Why is groundwater acidic?

Vocabulary

column

column

A cave deposit formed by the merging of a stalactite and a stalagmite.
groundwater

groundwater

Fresh water that moves through pore spaces and fractures in soil and rock beneath the land surface.
sinkhole

sinkhole

Circular hole in the ground that forms as the roof of a cave collapses.
stalactite

stalactite

Icicle-like formation of calcium carbonate from water dripping from the ceiling of a cave.
stalagmite

stalagmite

Deposit of calcium carbonate that grows upward in caves as water drips onto the floor.

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Date Created:

Feb 24, 2012

Last Modified:

Sep 23, 2014
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