![](media/image1.png){width="0.5834645669291338in"
height="0.75in"}Caves, Canyons, Cactus & Critters

*Middle School Geology*

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height="7.227777777777778in"}

Caves, Canyons, Cactus & Critters

Geology Curriculum

> **Hangy Downys, Sticky Upys, and Other Pretty Cave Decorations**\
> Activities that explore the origin of various cave formations. 65

1.  **Hangy Downys and Sticky Upys** An activity to grow stalactites\
    and stalagmites. 66

2.  **Not Just Your Average Decoration** A look at other special cave
    decorations (cave pearls, popcorn, corrosion features, etc.) 70

3.  **It's a Small World** A look at microclimates 73

4.  **Drip, Drip, Drip** A study of infiltration and water chemistry 78

5.  **A River Runs Through It\... Literally!** A look at another manner
    in\
    which caves can form. 82

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**Hangy Downys, Sticky Upys and Other Pretty Cave Decorations**

If you were to ask most people to describe a cave formation, they would
probably describe "hangy downys and sticky upys", more properly known as
stalactites and stalagmites. While these are probably the best-known
cave formations, caves contain many other fascinating formations as
well. Cave pearls, popcorn, hydromagnesite balloons, and selenite
crystals are just a few examples of other features that grow in caves.

Other features found in caves result from the corrosion of bedrock and
formations. These corrosion features are usually the result of the same
compound, carbonic acid, which resulted in the formation of the large
stalactites and stalagmites. However, the processes involved in
corrosion features are quite different. A key player in the development
of corrosion features is rising warm air.

A cave is a climate unto itself, and within a cave are many small
variations in that climate. These "microclimates" often result in
beautiful formations that can only occur in just the right set of
conditions. Typically, the microclimates are a result of air movement,
or the lack of it, within a cave system.

Water is another key player in the development of cave decorations.
Without it, the Carlsbad Cavern would be a rather barren hole in the
ground. Mildly acidic groundwater, migrating down through the limestone
bedrock, carried dissolved calcite to the cavernous voids where it was
deposited in the form of stalactites, stalagmites, and draperies. The
migration of water from the surface to the cave has been the topic of
many studies. A topic of concern recently has been the transportation of
pollutants from the visitor center and office area into the cave by
groundwater. Several studies have focused on determining the rate of
groundwater infiltration into the cave in many areas.

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**Hangy Downys and Sticky Upys**

***How do stalactites and stalagmites grow?***

**Summary:** Students will describe and model the formation of
stalagmites and stalactites.

**Duration:** Initial lesson and lab -- one class period with formation
growth going several days.

**Setting:** Classroom or lab

**Vocabulary:** flowstone, rimstone, speleothem, stalactite, stalagmite

**Standards/Benchmarks Addressed:** SC2-E3, SC4-E3, SC5-E2, SC6-E6

**Objectives**

Students will:

-   describe how stalactites and stalagmites form.

-   model stalactite and stalagmite formation.

**Background**

![](media/image4.wmf){width="1.4270833333333333in"
height="1.0416666666666667in"}The speleothems found in caves are formed
from many different minerals. In the book *Cave Minerals of the World*,
Carol Hill and Paolo Forti describe 255 different minerals that have
been identified in caves. Additionally, they describe 38 different types
of speleothems. Obviously, there is a lot more to cave minerals and
speleothems than just stalactites and stalagmites. This exercise is
designed to introduce students to the idea of minerals being carried in
solution from one location to another, where they are precipitated in
the form of a *speleothem*.

Rain or other precipitation falling in the Guadalupe Mountains absorbs
carbon dioxide from the air and from the soil as it seeps into the
ground. This causes the water to become slightly acidic. This water
infiltrates downward, first through pores in the soil and then through
cracks, or joints, in the bedrock. As the water encounters limestone, it
begins to slowly dissolve very small amounts of the calcite contained
there and carries it downward.

On reaching the cave, it can hang on the ceiling, run down the side of
the passage, or splash to the floor. Some of the carbon dioxide
contained in the water is released into the cave air. With this change
in the water chemistry, the calcite is no longer able to remain in
solution and begins to precipitate out as a solid. As the calcite
precipitates, the new crystals being formed attach themselves to
existing calcite crystals and the speleothems on which they are
deposited grow larger.

Sometimes the water will run, in a sheet, across the floor or down the
wall of the cave. As this water flows, carbon dioxide is lost to the
cave atmosphere and calcite will begin to precipitate onto the surface
the water is flowing over. Eventually, this will result in a smooth
calcite layer covering the original cave floor or wall. This layer is
called *flowstone* and is seen throughout the Carlsbad Cavern.

![](media/image5.wmf)

Often, water flowing across the floor of the cave will collect in pools.
As water flows over the edge of these pools to continue downstream, it
becomes turbulent. This causes carbon dioxide in the water to be
released to the cave atmosphere. As a result, calcite begins to
precipitate and attach to the edge of the pool. Over a period of time,
the buildup of calcite at the edge of the pool can build a dam, actually
deepening the pool. These *rimstone* dams, or gours, are found in many
of the caves of Carlsbad Caverns National Park. Possibly the most
spectacular of these is the Chinese Wall in Slaughter Canyon Cave.

The growth rate for speleothems varies from cave to cave and also varies
between locations within the same cave. According to Hill and Forti,
speleothem growth rates are affected by such factors as climate and
water infiltration patterns. They cite studies in which wide ranges of
growth rates were obtained for speleothems from several locations. In
one study, growth rates ranged from 0.22 to 9.29 cm/100 years. They
point out a study by Derek Ford in which he concludes that most cave
travertine (calcite) grew during the last half of the Pleistocene
Period, making it less than one million years old. However, in spite of
the variability of calcite growth rates, it is still a very slow process
on a human scale, with little growth being seen in the span of a human
lifetime.

Students often ask how to remember which formation is a *stalactite* and
which is a *stalagmite*. Stalactite has the letter 'c' in it like the
word ceiling. Stalactites hang from the ceiling. Stalagmite has the
letter 'g' in it like the word ground. Stalagmites grow from the ground.
Stalactites must hang on 'tite' or they will fall. If they keep growing,
stalagmites someday 'mite' reach the top of the cave. Most students will
be able to use one of these methods to help them remember the difference
in the two types of speleothem.

**Materials**

-   Epsom salts

-   small jars (two per set)

-   cotton yarn

-   washers or other items to be used as small weights

-   scissors

-   food coloring

-   spoon

-   aluminum foil

-   paper

**Procedure**

***Warm up:*** Show students photos of decorated cave passages. Have
them describe the speleothems that they see. Ask them to write a summary
of how they think the speleothems they see were formed.

Describe and discuss, as a class, the mechanisms by which the most
common calcite speleothems are formed. Discuss the slow rate of
speleothem growth and the factors influencing it.

***Activity***

1.  Prepare a saturated Epsom salt solution. This can be done by filling
    each jar 2/3 full with Epsom salt and adding water to the same
    height. Stir.

2.  Cut pieces of yarn 50 cm in length. Tie a weight to each end.

3.  Place each end of the yarn in different jars and press the weight to
    the bottom of the jar.

4.  Make a tray at least 60 cm long by folding and crimping the ends of
    a piece of aluminum foil.

5.  Place the jars on the tray. The string should hang between them with
    the lowest part of the loop 2-3 cm above the tray.

6.  Allow the jars to remain undisturbed for one week. Have the students
    check the speleothem growth daily. Have students draw the changes in
    the speleothems daily or plot the growth on a graph.

7.  If desired, food coloring can be added to the Epsom salt solutions.

***Wrap Up:*** Briefly, review the mechanisms of speleothem growth with
the students. Discuss the strong and weak points of the Epsom salt model
they have been observing for the past week. Tell the students that some
cave formations are formed from the same mineral as that contained in
Epsom salts. The mineral is called epsomite and has the chemical formula
MgSO~4~^.^7H~2~O. Epsomite speleothems grow much faster than calcite
speleothems. According to Hill and Forti, some epsomite speleothems have
been known to grow 25-35 cm in a matter of a few weeks.

**Assessment**

Have students

-   submit drawing or graphs demonstrating the growth rate of the
    epsomite speleothems made in class.

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-   describe how calcite speleothems like stalactites and stalagmites
    form.

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-   describe three factors that affect the growth rate of speleothems.

**Extensions**

Use the procedure described above to create Epsom salt speleothems, but
create them in a cave diorama. Several solutions with different colors
can be used. Place the jars on top of the box in which the diorama will
be built. Place the box on an aluminum foil tray or a shallow cookie
sheet. Make hole in the top of the box that the yarn will pass through
easily. Drape some pieces of yarn down through the box and back up to
another jar. Other shorter pieces of yarn can be suspended with one end
in a jar and the other hanging into the "cave." Encourage students to be
creative in attempting to replicate several varieties of speleothems.

**Resources**

Ambrose, Janet, et.al. *eds.* 1999. *About Bats, Caves and Deserts.*
Carlsbad, NM: Carlsbad Caverns National Park.

Hill, Carol and Forti, Paolo, 1997, *Cave Minerals of the World, 2nd
ed.* Huntsville, AL: National Speleological Society, Inc.

Jagnow, David and Jagnow, Rebecca. 1992. *Stories from Stones: The
Geology of the Guadalupe Mountains.* Carlsbad, NM: Carlsbad Caverns
Guadalupe Mountains Association.

Van Cleave, Janice. 1991. *Earth Science For Every Kid.* New York, NY:
John Wiley & Sons, Inc.

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**Not Just Your Average Decoration**

***Are there other types of formations that can be found in caves?***

**Summary:** Students will use information learned in class discussion
to model the formation of other cave decorations such as cave pearls,
popcorn, and corrosion features.

**Duration:** One 50-minute class for initial lesson. Five to ten
minutes daily for one to two weeks thereafter.

**Setting:** Classroom

**Vocabulary:** cave pearl, cave popcorn, condensation/corrosion,
frostwork, saturated

**Standards/Benchmarks Addressed:** SC2-E3, SC4-E3, SC5-E2, SC6-E6

**Objectives**

Students will:

-   describe how three other types of cave formations are formed.

-   build a model showing how cave popcorn is formed.

**Background**

![](media/image6.wmf){width="1.1666666666666667in"
height="1.3125in"}Caves contain many more speleothems than the
stalagmites and stalactites most people are familiar with. Three of the
other more common speleothems or features found in the caverns are cave
pearls, directional frostwork and popcorn (a form of coralloid), and
condensation/corrosion features.

Cave *pearls* grow in shallow pools of water saturated with the mineral
calcite. Sand grains, bat bones, rock, shell, wood fragments, or other
small pieces of calcite can form the nuclei around which the pearls will
grow. As carbon dioxide is lost to the air, calcite is deposited on the
object, as well as along the floor and edges of the pool. As more and
more calcite is added, the pearls will become rounded. Agitation,
typically from dripping water, is believed to keep the pearls from
adhering to the bottom of the shallow pool.

Directional *frostwork*, directional *popcorn*, and
*condensation/corrosion* features owe their existence to air circulation
within a cave. Directional frostwork and popcorn form as cool, drier air
descends into a cave during the winter months. For a detailed drawing
and discussion of seasonal air circulation in caves, see the lesson
*It's a Small World.* This drier air causes water to evaporate faster on
the side of formations facing the entrance of a cave. As the water
evaporates, calcite will precipitate and form the delicate frostwork
forms or the coral-like popcorn. Several good examples of directional
popcorn can be seen along the main passage in the Carlsbad Cavern
between the natural entrance and the Iceberg Rock. In this area, popcorn
grows on the entrance facing side of many stalactites and stalagmites.
Some passages in the Left-Hand Tunnel, between the Lunchroom and Lake of
the Clouds have excellent examples of directional frostwork.

Condensation/corrosion features are formed when carbon dioxide gas,
released from water in the cave, is absorbed by water condensed on the
cave wall or ceiling. According to Hill, three atmospheric conditions
must be present for this to occur: a high carbon dioxide level in the
air, high humidity in the air, and a temperature gradient, or
difference, between the air in different passages. The carbon dioxide is
released from pools in the cave, such as the Lake of the Clouds in
Carlsbad Cavern. If the air near the pool is warmer than air in another
upper passage, density driven air currents (see *It's a Small World*)
will cause the warmer, moisture and carbon dioxide laden air to rise up
to and along the ceiling. On reaching the ceiling and ceiling
formations, the water will begin to condense onto these cooler surfaces.
The carbon dioxide will dissolve into this fresh water, causing it to
become acidic and aggressive to the calcite bedrock and formations. Over
a period of time, the bedrock will become "punky," or soft and marked by
corrosion. Speleothems will be etched by acidic water along the side
facing into the rising airflow. The water (now saturated with calcium
carbonate, or calcite) can then be moved to the edge of the corroded
area by the gentle airflow. There, the carbon dioxide might again degas,
causing the calcite to precipitate and causing rims to grow along the
edge of the corroded area. This type of condensation/corrosion is very
evident on the Creeping Ear, located in the Lake of the Clouds Passage,
Carlsbad Cavern.

**Materials**

-   Carbonated soda in a transparent plastic bottle

-   Tap water

-   Carbonated water

-   White vinegar

-   Three small spray bottles

-   White chalk

-   Clay

-   Aluminum foil or small foil pans (about 10 cm diameter)

**Procedure**

This activity is designed to simulate condensation/corrosion processes
in caves.

***Warm up:*** While standing in the middle of the classroom, rapidly
shake the soda and act like you are going to open it. When students seem
to be concerned about this, ask why you shouldn't open the bottle.
Discuss the carbonation of sodas and how it causes soda to fizz. Ask
what happens if you leave the soda open overnight. Have students
hypothesize what happens to the fizz. Lead them to an understanding of
degassing, in which most of the carbon dioxide leaves the liquid and
returns to the air. Ask students what would they think would happen if
the degassed carbon dioxide encountered a drop of pure water with no
carbon dioxide in it. During the discussion, lead them to understand
that carbon dioxide will leave a soda where it is found in excess. It
will also reenter, or dissolve into, pure water.

Describe and discuss the carbon dioxide degassing that occurs from pools
in caves. Discuss the background material with students, being sure to
cover the manner in which the less dense, warmer air rises and carries
the carbon dioxide upward. Be sure to discuss the manner in which the
carbon dioxide dissolves into condensed water along the cave wall,
causing that water to become mildly acidic.

***Activity***

1.  Place three balls of clay (about 1\" diameter) in the bottom of
    separate aluminum pans. If using aluminum foil, fold the edges and
    tuck the corners to make trays about 10 cm long. Mark one of the
    pans "tap water," one of the pans "carbonated water," and the last
    "vinegar."

2.  Stick one piece of chalk upright in each of the balls of clay.

3.  In one spray bottle place tap water, in another place carbonated
    water, and in the third place vinegar. The carbonated water should
    be refreshed each day.

4.  Using the spray bottles, *lightly mist* each piece of chalk with the
    liquid for which it is labeled. Do not drench the chalk! Take care
    not to spray the other pieces of chalk.

5.  Place the pans where they will not be disturbed.

6.  Once per day, examine the chalk. Have the students record their
    observations using written descriptions, drawings, or photographs.

7.  Continue for one week, or until substantial differences can be seen.

***Wrap Up:*** Have the class summarize what they observed with the
chalk. Use class discussion or written work. Ask students to describe
the ways in which the demonstration they have done in class is similar
to the processes that occur in cave environments.

**Assessment**

Have students

-   describe condensation/corrosion features found in caves.

-   explain why popcorn is often found on the side of stalagmites facing
    the entrance of a cave.

**Extensions**

Using the Epsom salt speleothem model from the lesson *Hangy Downys and
Sticky Upys*, have students design and build a model of directional
popcorn. Remember that air currents used in the model must be very
light.

**Resources**

Hill, Carol, 1987, *Geology of Carlsbad Cavern and Other Caves in the
Guadalupe Mountains, New Mexico and Texas*. Socorro, NM: New Mexico
Bureau of Mines & Mineral Resources Bulletin 117.

Hill, Carol and Forti, Paolo, 1997, *Cave Minerals of the World, 2nd
ed.* Huntsville, AL: National Speleological Society, Inc.

Jagnow, David and Jagnow, Rebecca. 1992. *Stories from Stones: The
Geology of the Guadalupe Mountains.* Carlsbad, NM: Carlsbad Caverns
Guadalupe Mountains Association.

![](media/image3.png){width="0.6in" height="0.8346456692913385in"}

**It's a Small World**

***Why is the cave so cold and damp?***

**Summary:** Students will observe and describe microclimates around
their school.

**Duration:** One 50-minute class period

**Setting:** Classroom and around school

**Vocabulary:** circulation, dense, microclimate

**Standards/Benchmarks Addressed:** SC5-E2, SC6-E1, SC12-E7

**Objectives**

Students will:

-   describe various natural microclimates.

-   explain why caves are microclimates.

-   search for and describe microclimates found around their school
    building.

![](media/image7.wmf){width="1.0451388888888888in"
height="1.1875in"}**Background**

All caves have their own unique climates. These *microclimates*, as they
are called, are determined by many factors such as entrance elevation,
available moisture in the cave, shape and size of the passages, and mean
annual temperature. Seasonal variations in the airflow of Carlsbad
Cavern have resulted in a number of interesting directional speleothems
(see *Not Just Your Average Decoration* lesson). When air on the surface
cools during the fall and winter months, it becomes more *dense*. As the
air near a cave entrance becomes denser, it begins to flow into the cave
and down. It will continue to flow deeper into the cave until it reaches
the lowest level of the cave or meets a layer of air with the same
density. Meanwhile, the air in the cave is heated by the surrounding
rock, causing it to become less dense and rise. In this way, convective
cells of air circulation are set up in a cave system. Cool, drier
surface air sinks in along the lower portion of cave passages, while
warmer, more humid air from the cave rises along the ceiling toward high
points in the cave. A *circulation* cell like this is responsible for
the corrosion features found near Lake of the Clouds, Carlsbad Cavern.

This seasonal inflow causes seasonal fluctuations in temperature and
humidity along the main pathways leading to the depths of the cave.
However, along some passages, such as blind passages that have an
entrance, but no outlet, there is very little air circulation. In these
areas, the annual temperature and humidity variations are minimal.

Local tectonics and stratigraphy play a major role in the availability
of moisture in a cave. Perched aquifers can intercept infiltrating water
above one section of a cave and divert it to another. Additionally,
cracks in the bedrock, or joints, provide preferential pathways for
groundwater flow. Frequently these joints will cut across a perched
aquifer, providing a pathway for water to descend toward the cave. As
the groundwater flowing along joints intercepts a cave passage, a wetter
section of the cave will be formed. In that region, flowstone,
stalagmites, stalactites, draperies, columns, pools, and rimstone dams
may be abundant.

The entrance area of a cave is a special climate zone. The cooler
temperatures, increased humidity, availability of water, and shelter of
the rock make this zone a haven for desert wildlife. Cave swallows
frequently build nests along the cliffs found around cave entrances such
as Carlsbad Cavern. These birds can be seen returning from a day of
feeding just as the bats that live in the cave are leaving for a night
foraging in the desert skies. Ringtail cats, skunks, porcupines,
squirrels, and snakes are just a few of the other animals that enjoy the
special ecosystem that exists in a cave entrance. Insects, arachnids,
arthropods, and many smaller creatures thrive in the entrance as well.
Guano deposits usually mark the path leading from the bat roost area to
the entrance. Within these deposits, a microscopic world of living
organisms is found.

**Materials**

-   sling psychrometer (Celsius) NOTE: Alcohol thermometers are strongly
    recommended, rather than mercury!

-   thermometer (Celsius)

**Procedure**

***Warm up:*** Ask students to estimate the temperature outside. Ask
them to estimate the temperature inside the classroom. Ask them to
estimate the temperature in the principal's office. Ask if they believe
the air outside is more or less humid than the air inside.

Describe the concept of microclimates to the students. Point out that
around a school, several microclimates can exist. On a hot, summer day,
there can be a difference of several degrees between the hot, sunny,
south side of the building and the comparatively cooler, shady, north
side. Additionally, the humidity can vary in those areas as well. In
this lab, students will look for several different microclimate zones
in, and around, their school building. They will then compare those to
the microclimates found in caves.

***Activity***

1.  Have the student's list several places around the school building
    where they believe differences in temperature and humidity may be
    found. As a class, or in groups, select three or four of those
    locations to study.

2.  At each of those locations, record the temperature and the wet and
    dry bulb readings from the psychrometer. Remember, the fabric sock
    on the wet bulb of the psychrometer must be moistened prior to use,
    preferably with distilled water. The psychrometer must then be spun
    gently for several minutes and checked periodically. This continues
    until the wet bulb temperature stabilizes.

3.  Inexpensive sling psychrometers are available from several science
    supply houses. Some thermometers have a small eye at the top to
    which a string could be attached. However, this is not recommended,
    as these eyes tend to break fairly easily under these conditions.
    Simple student psychrometers can be built by taping, or gluing,
    small, inexpensive thermometers to a support, such as a thin piece
    of wood, and attaching a sock made of gauze to the bulb. The dry
    bulb temperature can be obtained from the regular thermometer being
    used to determine air temperature. Once the students have obtained
    their data, they can determine the relative humidity of their
    microclimate zones by using the data table provided with the
    psychrometer, or the data table provided at the end of this session.
    On the data table, they will need to find the dry bulb temperature
    along the vertical axis. They will need to calculate the difference
    in the wet and dry bulb temperatures and find this value on the
    horizontal axis of the table. Once both numbers have been found, the
    relative humidity can be determined.

![](media/image8.wmf)

***Wrap Up***

Discuss any difference in temperature and relative humidity that the
students observed.

Have the students attempt to explain why those differences were found.
They should consider such things as shading, protection from wind,
proximity to a source of moisture (leaky faucet, condensation dripping
from evaporative cooler, evaporative coolers, etc.).

Have students list any factors they can think of that would be
responsible for the existence of microclimates in a cave. Have them list
and describe the consequences of several possible microclimates. As an
example, a high amount of water and drier, inflowing air will result in
increased evaporation and more speleothems.

End with a discussion of the various organisms that utilize the unique
ecosystem and microclimate found in and near the entrance of a cave.

**Assessment**

Have students:

-   describe several factors that contribute to the development of
    microclimates in caves.

-   describe procedures and equipment that might be used by
    speleologists when studying microclimates in caves.

**Extensions**

Have students:

-   Use the equipment from this lab to study microclimates around their
    community and to evaluate the impact these microclimates have. As an
    example, the Bataan Bridge crosses the Pecos River in Carlsbad, New
    Mexico and underneath a very interesting microclimate is found. The
    area under the bridge is slightly more humid, cooler, and darker. As
    a result, it is home to a healthy population of swallows and bats.
    It the water of the Pecos, the bridge also modifies the climate by
    creating shaded, cooler zones in the water. Fish are frequently
    found in these shaded areas during the hot, sunny summer months.

**Resources**

Feather, Ralph, et al. 1999. *Glencoe Earth Science.* Westerville, OH:
Glencoe/McGraw-Hill. (Contains a lab activity for using a sling
psychrometer on pp. 428-429, 719.)

Hill, Carol, 1987, *Geology of Carlsbad Cavern and Other Caves in the
Guadalupe Mountains, New Mexico and Texas*. Socorro, NM: New Mexico
Bureau of Mines & Mineral Resources Bulletin 117.

**Relative Humidity in Percent**

**It's a Small World**

  ------------------- -------------- ------- ------- ------- ------- ------- ------- ------- ------- -------- -------- -------- -------- -------- --------
  ***T~db\ ~*(°C)**   **Dry Bulb -                                                                                                                
                      Wet Bulb                                                                                                                    
                      Temperatures                                                                                                                
                      (°C)**                                                                                                                      

                      **1**          **2**   **3**   **4**   **5**   **6**   **7**   **8**   **9**   **10**   **12**   **14**   **16**   **18**   **20**

  **2**               84             68      52      37      22      8                                                                            

  **4**               85             70      56      42      29      26      3                                                                    

  **6**               86             73      60      47      34      22      11                                                                   

  **8**               87             75      63      51      39      28      18      7                                                            

  **10**              88             76      65      54      44      33      23      14      4                                                    

  **12**              89             78      67      57      47      38      29      20      11      3                                            

  **14**              89             79      69      60      51      42      33      25      17      9                                            

  **15**              90             80      71      62      54      45      37      29      22      14                                           

  **18**              91             81      73      64      56      48      41      33      26      19       6                                   

  **20**              91             82      74      66      58      51      44      37      30      24       11                                  

  **22**              91             83      75      68      60      53      46      40      34      27       16       5                          

  **24**              92             84      76      69      62      55      49      43      37      31       20       9                          

  **26**              92             85      77      70      64      57      51      45      39      34       23       14       4                 

  **28**              92             85      78      72      65      59      53      47      42      37       26       17       8                 

  **30**              93             86      79      73      67      61      55      49      44      39       29       20       12       4        

  **32**              93             86      80      74      68      62      56      51      46      41       32       23       15       8        1

  **34**              93             87      81      75      69      63      58      53      48      43       34       26       18       11       5

  **36**              93             87      81      75      70      64      59      54      50      45       36       28       21       14       8

  **38**              94             88      82      76      71      65      60      56      51      47       38       31       23       17       11

  **40**              94             88      82      77      72      66      62      57      52      48       40       33       26       19       13

  **42**              94             88      83      77      72      67      63      58      54      50       42       34       28       21       16

  **44**              94             89      82      78      73      68      64      59      55      51       43       36       29       23       18
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![](media/image3.png){width="0.6in" height="0.8346456692913385in"}

**Drip, Drip, Drip**

***How long does it take water to get from the surface into the cave?***

**Summary:** Students will explore infiltration rates and the factors
that affect it.

**Duration:** Two 50-minute class periods

**Setting:** Classroom or lab

**Vocabulary:** infiltration, groundwater, porosity, permeability,
aquifer, aquiclude, water table, zone of aeration, zone of saturation

**Standards/Benchmarks Addressed:** SC2-E3, SC5-E2, SC6-E1, SC12-E7

**Objectives**

Students will:

-   describe factors influencing infiltration rates.

-   build a model demonstrating the effect of different soil and rock
    types on infiltration.

![](media/image9.wmf){width="0.6555555555555556in"
height="1.4145833333333333in"}**Background**

Much of the material in this lesson will duplicate that from *It's More
Than Just Dead Dinosaurs!* That is because the ideas of porosity,
permeability, and the flow of fluids through rock reservoirs are
basically the same. The activity involves the use of the same bottles to
model fluid flow underground.

As precipitation falls to the ground, one of three things can happen to
it. It can evaporate and return to the atmosphere as water vapor.
Sometimes this happens after the water has been intercepted and held on
vegetation for a period of time. It can also happen as water evaporates
from puddles left by a rainstorm or as the water held in muddy soil is
drawn out and given the energy to evaporate by the sun. Other water can
infiltrate into the ground, percolating downward to become
*groundwater*. That which does not evaporate or infiltrate begins to
seek low spots and, in the process of moving across the ground, becomes
what is called runoff. Runoff can range from large rivers, such as the
Mississippi River, to small rills along the edge of a mud puddle in a
student's backyard.

This lesson will focus on *infiltration*. The principle factor affecting
the rate of infiltration is the composition of the soil. As water begins
to infiltrate it fills the openings, or pores, in the soil as it moves
downward. Some soils contain gravel or sand. In these soils, the pores
will be larger and the soil will be more *permeable*. This means that
the water can move through the soil faster. The openings are smaller in
soils with silt or clay sized particles. Water will move slower through
these soils. Additionally, molecular attraction between water molecules
and clay particles further slows the rate of infiltration. If the rate
of precipitation exceeds the rate of infiltration, the ground becomes
saturated with water. That is, all of the pore spaces in the soil fill
with water. When this happens, any excess water begins to flow down
gradient across the surface as runoff.

As water infiltrates downward, it will eventually reach a permeable
layer in which groundwater is stored. This layer is called an *aquifer*.
In the aquifer, the region in which most spaces are filled with air is
called the *zone of aeration*. The region in which most spaces are water
filled is called the *zone of saturation.* The top of the zone of
saturation is referred to as a *water table*. The aquifer is bordered on
the bottom, and sometimes on the top, by an impermeable layer called an
*aquiclude*. Sometimes, a small aquiclude will be found higher than the
main water table for a region and a small aquifer will form. These small
aquifers found higher than the main regional water table are called
perched aquifers. The area from which an aquifer receives water in the
form of infiltrating precipitation is called the recharge zone.

![](media/image10.wmf)

Joints, or cracks, in the rock provide the main form of *porosity* along
which groundwater infiltrates into the Carlsbad Cavern and other caves
of the park. Evidence of this can be found by observing the long lines
of stalactites, stalagmites, and columns formed along some of the major
joint systems that cross the caves. However, recent research has shown
that the infiltration rates are not uniform throughout the cave. A
recent study seemed to indicate that some of the deeper sections of the
cave actually see meteoric waters that infiltrate at a faster rate than
some of the shallower sections of the cave. At this time, these studies
are ongoing.

The location of the visitor center and offices over the Carlsbad Cavern
has been a cause for concern for several years. Due to the location of
these facilities, many sources of potential pollution exist directly
above the cave. Runoff from the parking concentrates oil, anti-freeze,
and other pollutants into areas where the water leaves the parking lot
and infiltrates into the surrounding desert soils. Septic systems and
leaking sewer lines have also been found to be potential sources of
pollutants on the surface. Studies have shown that some of these
pollutants are reaching the cave as infiltrating waters carry them down.
As a result, proposals have been made to move some, or all, of the
facilities to the bottom of the escarpment where they would no longer
pose a threat to the water entering the Carlsbad Cavern.

**Materials**

-   graduated 250 ml beakers -- 3

-   100 ml beakers -- 3

-   several 2- or 3-liter soda bottles

-   sand (several colors, if possible)

-   gravel (several colors, if possible)

-   scoria (holy lava rock, batman!)

-   clay

**Procedure**

***Warm up:*** This activity is almost identical to *It's More Than Just
Dead Dinosaurs!* However, it focuses on groundwater, rather than oil and
gas migration.

Discuss the concept of groundwater, infiltration, and the movement of
groundwater with the class. If possible, secure a groundwater model to
use with the class discussion or bring in a speaker with groundwater
experience. Your local Soil and Water Conservation offices, county
extension office, National Park Service personnel, Forest Service
Personnel, or Bureau of Land Management personnel may have the expertise
and materials to help with this.

Discuss the role of infiltrating water in cave development and potential
hazards posed by the infiltration of polluted water.

***Activity***

1.  Set up three bottles as shown in the activity *It's More Than Just
    Dead Dinosaurs!*

![](media/image11.wmf)

a.  Cut the bottom 3 or 4 inches from three 3-liter bottles and turn
    them over.

b.  Glue a single layer of cloth into the bottom of each to keep the
    sand and gravel from coming out.

c.  Fill the bottles as shown.

    1.  Turn all three bottles upside-down with a graduated 250 ml
        beaker under each. Ask the students, "If I pour 100 ml of water
        into each of these at the same time, which will it travel
        through fastest?" Be open to all suggestions. Have the students
        justify their guesses. Have students assist you and pour 100 ml
        into each bottle at the same time. Monitor the 250 ml beakers to
        see which bottle the water passes through fastest. Discuss the
        results with the class. Solicit their hypothesis regarding the
        different rates of infiltration through the bottles.

    2.  Define porosity for the students. Show students a piece of
        scoria (lava rock with holes in it), a piece of sandstone, and a
        piece of conglomerate or a handful of gravel. Ask which of the
        samples exhibit porosity. Students should answer "all three."
        Ask which would form a rock through which fluids would move the
        easiest. Some students may select the scoria, due to the size of
        the pores. Point out to students that even though all three
        samples have porosity, the holes are not connected in the
        scoria, so fluid would not move through it as easily. The pores
        in the gravel are bigger than the pores in the sand or
        sandstone, so fluid would move through the gravel easier.
        Discuss the differences in porosity and permeability.

    3.  Ask the students what happen if the water reached an opening,
        like a cave. Have them describe what might happen to the
        dissolved minerals in the water as it hangs from the ceiling of
        a cave passage. Have them explain where those minerals come
        from.

    4.  Ask the students, "If the water is moving through the ground in
        a permeable layer of rock, what could stop it?" Entertain all
        suggestions. Describe aquifers and aquicludes to the students.
        Using overhead or board drawings, demonstrate and discuss zone
        of aeration, zone of saturation, aquifer and aquiclude.

***Wrap Up:*** Review the role of groundwater in cave formation.

Ask the students where they get the water they drink. Lead to a
discussion of how the water must come from a surface reservoir or from a
well before it makes it to them. Discuss potential sources of pollution
along that pathway and what should be done to protect their drinking
water.

**Assessment**

Have students:

-   describe the conditions necessary for an aquifer to form and for
    groundwater to move through it.

-   explain how pollution could get into a cave system that has no
    entrance.

**Extensions**

-   Build several bottle models and test other materials to see which is
    the most permeable.

-   Conduct research on the local drinking water system. Have students
    find out where it comes from, how it is treated, etc.

-   Study the local wastewater treatment system. Where does it go after
    you flush? How is it treated? What eventually happens to the water?
    Try to fit this in to a very large-scale discussion of the water
    cycle (There is no new water, just used water).

**Resources**

Chernicoff, S., Fos, H.A., and Venkatakrishnan, R. 1997. *Essentials of
Geology.* New York, NY: Worth Publishers.

Feather, Ralph, et al. 1999. *Glencoe Earth Science.* Westerville, OH:
Glencoe/McGraw-Hill.

Murck, B.W., Skinner, B.J., and Porter, S.C. 1996. *Environmental
Geology.* New York, NY: John Wiley & Sons, Inc.

![](media/image3.png){width="0.6in" height="0.8346456692913385in"}

**A River Runs Through it\... Literally!**

***How do some other caves form?***

**Summary:** Students will describe the processes in which caves are
formed as moving water dissolves bedrock.

**Duration:** Initial lesson will take one 50-minute class with 5-10
minutes per day for several days after.

**Setting:** Classroom or lab

**Vocabulary:** karst, dissolve, soluble

**Standards/Benchmarks Addressed:** SC2-E3, SC5-E2, SC6-E1

**Objectives**

Students will:

-   build a model of a cave or karst valley formed in bedrock dissolved
    by moving water.

-   describe the processes by which moving water forms karst valleys or
    caves.

**Background**

![](media/image12.png){width="1.3645833333333333in"
height="2.0416666666666665in"}Most of the caves in Carlsbad Caverns
National Park were formed when rising H~2~S gas from the Delaware Basin
oxidized to form sulfuric acid near the water table (see the lesson
*Stinky Gas and Alabaster*). This acid *dissolved* the limestone rock of
the ancient Capitan Reef and the caves were created. However, most caves
are not formed that way. Many of the gypsum caves on the Eastern Plains
of New Mexico were formed as water, moving through joints in the gypsum
bedrock, dissolved the rock, forming passages. Most of these gypsum
caves only see water during the monsoon season when heavy rainfall from
thunderstorms or prolonged rain floods them. However, some of the caves
actually contain water year-round in the form of streams and pools. As
the water makes its way through the cave system, it will eventually join
a deep aquifer or resurface at a karst spring. Many of the big pools on
the Delaware River near Carlsbad Caverns National Park are fed by these
karst springs.

The longest cave in the world, Mammoth Cave, is found near Bowling
Green, Kentucky. Much of Mammoth Cave lies within the borders of Mammoth
Cave National Park. The bedrock in which the Mammoth Cave system was
formed is limestone. As the meteoric waters infiltrated into the ground,
they began to absorb carbon dioxide and became mildly acidic. This
acidic water then began to dissolve the rock through which it was
passing. Eventually, traversable passages were formed. With a total
surveyed length of well over 300 miles, Mammoth Cave was formed from the
interconnecting passages of many underground streams and rivers. These
streams eventually fed into the Green River, the base level river for
the area. Over the years, the Green River cut deeper and deeper into its
canyon bottom. As it cut deeper, the streams and rivers forming Mammoth
Cave also cut deeper. As a result, Mammoth Cave is formed on several
levels, all corresponding to the down cutting of the Green River. In
much of the United States, the caves that are found have been formed in
this manner. Large numbers of limestone caves are found in the eastern
US, on the Ozark Plateau, and in central Texas. Caves have not formed in
this manner in the limestone of the Guadalupe Mountains in New Mexico
and Texas. This is primarily due to the low amount of precipitation each
year.

The gypsum caves of New Mexico and Mammoth Cave of Kentucky were formed
by similar processes. However, they are formed on different time scales.
Gypsum is typically ten times more *soluble* in water containing CO~2~
than limestone is; depending on how much CO~2~ is in the water. This
means that gypsum caves will form at a faster rate than similar
limestone caves.

Lave tubes are another type of cave found in New Mexico and other areas
of the western US. Lava tubes are formed on the flanks of shield
volcanoes. As lava flows away from a volcanic vent, that which is near
the surface begins to cool and harden. Eventually, a seemingly solid
surface can form. However, under that solid crust, liquid lava can still
flow. As the eruption dies out, the level of the liquid lava will drop
and a tube, or lava cave, will be left behind. Access to these caves is
often gained through holes where the ceiling has collapsed.

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*. While the development of
sinkholes and other karst features may not be much of a problem in
southeastern New Mexico, it is a big problem in Florida and on the
Sinkhole Plain of Kentucky. Roadways and houses have been swallowed by
sinkholes in these states. 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. The Hidden River Cave system under Bowling
Green, Kentucky, was such a problem. Cleanup efforts have improved the
status of the cave, but pollution is still a constant threat. Most of
the karst aquifers in the US are threatened due to pollution and
development on the surface.

For more information on karst and cave development, refer to the lesson
*Natural Acids*.

**Materials**

-   sugar cubes

-   distilled water

-   cake pan

-   dropper or bottle with sports lid that can slowly drop water

-   photos of various types of caves

**Procedure**

***Warm up:*** Have the students compare and contrast the various types
of caves shown in the photos.

Describe the various processes of cave formation to the students.

***Activity***

1.  Very lightly moisten the edges of the sugar cubes and stick them
    together on a cake pan or cookie sheet in a block 10 cubes wide x 5
    cubes high x 20 cubes long (or whatever size you prefer).

2.  Lift one edge of the pan or sheet 1 to 2 inches to give it a gentle
    slope. The pan will represent an impermeable lower layer of rock.

3.  Select a point on top of the sugar block, near the upper end, on
    which you will slowly begin to drop water.

4.  Begin slowly dropping water on the pre-selected spot at a rate of
    about 5 ml per day.

5.  Over the course of several days, have students document the change
    in the block as the sugar is dissolved.

6.  If you schedule does not allow for several days of observation,
    increase the rate at which you apply the water.

***Wrap Up:*** Ask students what it would be like to live in an area
where caves are actively forming underneath you. Discuss problems faces
by those living in Florida and on the Sinkhole Plain near Bowling Green,
KY.

**Assessment**

Have students:

-   describe the processes that form caves like Mammoth Cave in
    Kentucky.

-   describe the problems associated with living in an area where caves
    are actively forming.

**Extensions**

Have students build several sugar blocks and apply water at different
rates. Have students monitor and document their observations. Lead
students to draw conclusions about the possible effects of annual
rainfall on the rate at which karst features form.

**Resources**

Moore, George, and Sullivan, Nicholas. 1978. *Speleology: The Study of
Caves.* Teaneck, NJ: Zephyrus Press, Inc.

Veni, George, et.al. 2001. *Living With Karst.* Alexandria, VA: American
Geological Institute Environmental Awareness Series, 4.