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

*Middle School Geology*

![](media/image2.jpeg){width="5.220138888888889in"
height="7.227777777777778in"}

Caves, Canyons, Cactus & Critters

Geology Curriculum

> **Mother Nature's Gravel Company** Activities designed to introduce\
> the topics of weathering and erosion. 52

1.  **Ice Wedgies!** An activity designed to study the effect of\
    freeze/thaw cycles on rock. 53

2.  **Huff 'n' Puff** A lab designed to study the effect of obstacles\
    on sand dune migration. 55

3.  **Flash Flood Fantasy** A lab that demonstrates the effects\
    of erosion and deposition in the Basin and Range region of the\
    US southwest. 59

4.  **Nature's Acids** A look at how natural acids contribute to cave\
    formation. 62

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

**Mother Nature's Gravel Company**

Anyone hiking the backcountry of Carlsbad Caverns National Park will
immediately notice that it's very rocky. Big angular rocks breaking off
cliffs on the hillsides, round, bowling ball size rocks, and sand and
gravel bars in the canyon bottoms all make up a major part of the
landscape. The processes that take the limestone, sandstone, and shale
bedrock of the Guadalupe Mountains and turn them into smaller sediments
are called weathering and erosion.

The processes that break rocks into smaller pieces are referred to as
weathering. Mechanical weathering breaks the rocks into smaller pieces
without changing their chemical composition. Examples of mechanical
weathering are root pry, ice wedging, abrasion, and differential
heating. With chemical weathering, the chemical composition of the rock
is changed. Examples are reactions with water, acids, and oxygen. The
smaller pieces of rock that result from weathering are called sediment.
In Carlsbad Caverns National Park, all of these processes are active.

The processes that move sediments are referred to as erosion. The
primary agents of erosion are wind, water, gravity and ice (glaciation).
In Carlsbad Caverns National Park, all of these, except ice, are active
processes.

In this unit, activities will explore weathering by ice wedging and by
acids, two of the most active processes in the park. Erosion by wind and
water will be the subjects of activities as well.

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

**Ice Wedgies!**

***What breaks rocks apart in the mountains?***

**Summary:** Students will model the effect of freeze/thaw cycles on the
weathering of rocks.

**Duration:** Part of two 50-minute class periods with overnight
activity.

**Setting:** Classroom

**Vocabulary:** abrasion, differential heating, ice wedging, mechanical
weathering, root pry

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

**Objectives**

Students will:

-   describe the four major types of mechanical weathering.

-   model ice wedging.

**Background**

![](media/image4.wmf){width="0.9166666666666666in"
height="1.0416666666666667in"}The processes by which a rock is broken
into smaller pieces without being changed chemically are called
*mechanical weathering.* The most common of these processes are *root
pry*, abrasion, differential heating, and ice wedging. When a plant's
root grows through a crack in a rock, it begins to exert a gradual
pressure on the sides of that crack. Slowly, over time, the pressure
increases and the crack widens until, eventually, the rock is broken.

*Abrasion* is the wearing away of rocks by solid particles carried by
wind, water, or other forces. Classic examples of weathering can be
found at Arches National Park, Zion National Park, and Bryce Canyon
National Park. In all of these Utah parks, sand carried on the wind has
carved unusual shapes and spectacular windows. Along the bottoms of the
canyons in the Guadalupe Mountains in Texas and New Mexico are places
where the bedrock has been scoured smooth by abrasives carried in
floodwater.

*Differential heating* is the stress created within a rock when the
outer part of the rock expands and contracts with daily heating while
the interior of the rock remains stable. The stresses generated by this
flexing eventually cause layers or sheets to break loose and peel away
from the surface of the rock. Another form of differential heating
called intergranular disintegration occurs in rocks composed of a mix of
light and dark colored minerals. When exposed to sunlight, dark colored
minerals absorb more of the energy than the light minerals and heat at a
different rate. This difference in heating rates, combined with
differences in thermal expansion rates, causes stress between the
mineral crystals. With the cycle repeated daily over several years, the
crystals eventually break apart from one another. Running your hand
across granite or diorite weathered this way will yield a handful of
crystals resembling salt and pepper.

*Ice wedging* begins when water seeps into cracks in a rock. It is
dependent on cycles of nightly freezing and daily thawing of that water.
As the water freezes at night and changes state from a liquid to a
solid, the molecules of H~2~O align into a repeating pattern known as an
ice crystal. This orderly arrangement of molecules takes up more space
than the same molecules in a liquid state. Due to this, the ice expands
approximately 9% and exerts great pressure on the sides of the crack.
During the day, the water melts, possibly more water seeps into the
crack, and the cycle begins again. As these freeze/thaw cycles continue
over a span of years, the crack continues to widen until the rock is
broken. This method is most effective in regions that have a maximum
number of freeze/thaw cycles throughout the course of a year. During the
late fall to early spring months, this would be an active process in the
high Guadalupe Mountains.

**Materials**

-   plastic one-liter soda bottles (one per three or four person group)

-   marker that will mark on plastic bottle

**Procedure**

***Warm up:*** Ask students to describe any processes they can think of
that would turn big rocks into small rocks in nature. List and discuss
these ideas.

Describe and discuss root pry, abrasion, and differential heating.

Discuss the concept of ice wedging.

***Activity:*** This activity will involve leaving items in a freezer
overnight.

1.  Pour about 800 ml water in one-liter soda bottles and put cap on.

2.  Mark the water level on the side of the bottle.

3.  Place all bottles in a freezer overnight. Set them in a pan or
    container that can hold the volume of water used, just in case.

4.  Remove bottles from freezer immediately prior to use in class.

5.  Have students mark level of ice in the bottle and make note of any
    deformations they see on the bottle.

***Wrap Up:*** Discuss what was observed. Have the students hypothesize
why the volume of water increases when it becomes ice.

Ask if any student has ever had pipes freeze and burst during winter.
Discuss the effect that freezing would have on anything containing
water.

Review ice wedging and incorporate observations from the lab into the
discussion.

**Assessment**

Have students:

-   list the forms of mechanical weathering.

-   describe the processes by which the forms of mechanical weathering
    work.

**Extensions**

Have students design and perform experiments or demonstrations modeling
one of the three other forms of mechanical weathering mentioned in the
background material.

Have students make a list of any examples of mechanical weathering they
observe over the course of one week.

**Resources**

Coble, Charles, et al. 1993. *Prentice Hall Earth Science.* Englewood
Cliffs, NJ. Prentice Hall.

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

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

**Huff 'n' Puff**

***Why and how do sand dunes form?***

**Summary:** Students will use information learned in class discussion
to model sand dune migration.

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

**Setting:** Classroom

**Vocabulary:** abrasion, deflation, deposition, desert pavement, slip
face

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

**Objectives**

Students will:

-   describe how sand dunes form.

-   describe the effect of obstacles on sand dune migration.

**Background**

![](media/image5.wmf){width="2.1770833333333335in"
height="1.3645833333333333in"}Energy is defined as the ability to do
work or to move a mass a distance. Anyone who has been around the
Carlsbad area during spring knows that, by this definition, wind has
energy. Wind regularly fills the air with dirt and debris it has picked
up and moves the debris to new locations.

Two words used to describe erosion by wind are deflation and abrasion.
When the wind blows across loose particles and picks up or moves the
smaller ones, it is referred to as *deflation.* When wind-borne objects
strike stationary objects or sediment and loosen them so that they too
are eroded, it is referred to as *abrasion*. *Deposition* occurs when
the wind slows and loses energy. Without the energy it once had, the
wind can no longer carry the sediments it once did and they begin to
settle to the ground.

Several factors can make it difficult for wind to pick up sediments.
Sediment size is one such factor. As the wind blows across an area
containing several sizes of loose sediment, it begins to carry away the
smaller particles, leaving the larger ones behind. Over time, these
larger sediments will form a protective coating on the ground,
preventing the wind from further deflating the smaller sediments. This
protective layer is called *desert pavement* and is seen in the Carlsbad
Caverns National Park area.

Two other factors affecting the ability of wind to deflate sediments are
vegetative cover and moisture. Vegetative cover protects the soil under
it from wind and helps to keep the soil moist. When sediments are moist,
they will remain packed and resistant to deflation. When vegetation is
removed, the soil is exposed to the sun. As the soil begins to dry, it
can be deflated easier by the wind. In a time of drought, this is a
natural process. A lack of rainfall will cause vegetation to die. As it
dies, the soil underneath will be exposed to the wind and eroded. Any
human activity that disrupts vegetative cover can also accelerate wind
erosion. Such activities are surface mining, farming, and construction.
During the 1930s, in the central part of the United States, farmland was
left in an unvegetated state due to drought. Wind moving across these
fields deflated great quantities of topsoil and carried it as far as New
England and the North Atlantic Ocean. Today, in an effort to prevent or
slow these "dust bowl" type storms, windbreaks are often planted along
fields. Windbreaks are typically rows of trees planted between fields.
These rows of trees disrupt and slow the flow of air at ground level and
inhibit its ability to deflate soil in fields.

The wind deposit with which most people are familiar is sand dunes. Sand
dunes are mounds of sand that migrate in directions dictated by the
prevailing winds in an area. As the wind moves across the windward side
of the dune, the side with the more gradual slope, it deflates, the
sediments on that side of the dune and carries or bounces them up the
dune to the top. As the wind moves across to the back, or leeward, side
of the dune, its speed slows and it looses energy. This steeper side
where sediments are deposited is referred to as the *slip face.* Near
the dune, the wind will form eddies, or backward rotating areas. In
these lower energy areas, sand carried from the front of the dune will
be deposited. In this way, the dune migrates in the direction the wind
is blowing.

![](media/image6.wmf)

**Materials**

-   sand

-   flour

-   gravel

-   rocks 1\" - 2\" diameter

-   9\" x 13\" baking pans or similar size tubs

-   soda straws

-   cardboard sheets

-   tape

-   paper for sketching

**Procedure**

***Warm up:*** Define energy for the class. Ask for examples of things
in nature that have energy. For each example, ask for proof.

If students do not suggest it, ask, "Does wind have energy?" Answers may
vary. If some students say no, you may want to ask about such things as
sailboats, tornadoes, and springtime in the southwest.

Once it has been established that wind does have energy, discuss
deflation, abrasion and deposition. Ask students for examples of ways to
keep the wind from eroding soils. Discuss the dust bowl conditions of
the 1930s. Describe desert pavement and ask where students think it
might be found.

Ask students if anyone has ever visited sand dunes anywhere, including
White Sands National Monument, Great Sand Dunes National Monument, or
the sand dunes east of Carlsbad, New Mexico. Ask about the shape of the
dunes. Describe and discuss sand dune movement.

***Activity***

1.  Mix the sand, gravel, and flour thoroughly.

2.  Cover the bottom of a pan or washbasin with 1/2 inch of the mixture.
    Put one or two of the rocks in the pan near the middle. Use one
    setup per group of two to four students. Allow the students to
    "sculpt" the landscape in any form they choose but establish the
    guideline that once the wind starts blowing, they cannot touch the
    sediments in the pan again.

3.  Have students use three or four pieces of cardboard and tape to
    construct a barrier around their "dune field."

4.  Using the straw, students will ***GENTLY*** blow the sand from one
    side of the pan. *The wind must always come from the same side
    throughout the activity*. Tell students that if the sediments are
    not moving, they need to make more wind. If their table looks like a
    field during the dust bowl days, they do not need as much wind.

5.  Have students sketch their dune field four or five times during the
    activity at an interval of about three or four minutes between
    sketches. The first sketch should be drawn before beginning. In
    particular, have them sketch dunes and how they change, areas of
    deflation and deposition, what happens to sediments around the
    larger rocks, formation of desert pavement, and any place they see
    the sediments being sorted by size.

***Wrap Up:*** After cleaning sand and flour off of tables or desks, ask
students who have been to sand dunes if the features they saw in their
pan looked familiar to what they have seen at areas with sand dunes. Ask
students for examples of other areas where they've seen sediments pile
up along the side of an object like the rock in their pan. Some examples
might be along a street curb during a dust storm, and around the side of
a house or fence during a sand storm or during a snowstorm.

Ask the students what can be done to prevent wind erosion. Suggestions
should include planting vegetation and windbreaks.

**Assessment**

Collect sketches. Have students:

-   define and explain *deflation, abrasion* and *deposition.*

-   list three factors affecting wind erosion.

-   describe two ways to prevent or slow wind erosion.

-   describe how a sand dune moves.

**Extensions**

Have students:

-   do internet or library research and gather photos of sand dunes from
    around the world.

-   study the photos and attempt to determine the prevailing wind
    direction.

-   identify any features in the photo designed to stop or slow wind
    erosion.

-   compare and contrast the dunes to determine if dunes can have
    several different basic shapes. Have them research the various dune
    shapes (barchan dunes, transverse dunes, parabolic dunes, seif
    dunes, star dunes, dome-shaped dunes, and reversing dunes) and
    attempt to determine what types are found in each of the photos.
    (Barchan and seif are the most common)

**Resources**

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

VanCleave, Janice. 1991. *Janice VanCleave's Earth Science For Every
Kid.* New York, NY, John Wiley & Sons, Inc.

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

**Flash Flood Fantasy**

***Why is water the primary agent of erosion in the arid southwest?***

**Summary:** Students will observe and describe gully and canyon erosion
in the desert southwest using stream trays they have made.

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

**Setting:** Classroom and outside

**Vocabulary:** alluvial fan, arroyo, bar, canyon, meander, undercut
bank, waterfall

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

**Objectives**

Students will:

-   name features formed by moving surface water.

-   describe erosion features formed in stream trays or canyon models.

**Background**

![](media/image7.wmf){width="1.4375in" height="1.84375in"}The four
primary agents of erosion are wind, water, gravity, and ice. Of these,
the most active on the earth's surface is water. Even in the semi-arid
southwestern United States, water does more to sculpt the land than
wind, ice, or gravity. Most of the precipitation in the area around
Carlsbad Caverns National Park comes in the form of brief, heavy
rainfall associated with thunderstorms. From a small, obscure mudflow
along the flanks of North Slaughter Canyon to a road-blocking flash
flood in Walnut Canyon, the effects of these periodic, intense rains can
be seen throughout the park.

Most of the deposits and landforms seen along valleys where rivers flow
year-round are similar to or identical to those formed by periodic
flooding in the desert southwest. Among these are *canyons, arroyos*,
*waterfalls*, meanders, bar deposits, undercut banks, and, at the mouths
of canyons, alluvial fans. Canyons, arroyos, and falls are features
familiar to anyone who has spent time in the mountains near a river that
meanders its way past, flowing downhill. In fact, a bend in a river is
called a *meander.* The deposits of rocks, gravel, and sand, rounded by
the abrasive action of fast moving floodwater, are called *bars*. A
close examination of bar deposits will reveal that the sediments in a
bar deposit are sorted by size. As the water in a river or a flooding
canyon flows around, over, and through obstacles, its velocity changes.
These changes in velocity and energy result in sediments being sorted,
or deposited in different places along a stream or canyon bottom. Often,
the fast moving water along the outer edge of a meander will cut into
the bank, leaving soil and plants or trees above. When this happens, it
is referred to as an *undercut bank*.

As a flash flood roars down a canyon in the Guadalupe Mountains, or in
similar fault-block mountains, it has a great deal of energy and moves
sediment that is large in volume and large in size. Mountains like the
Guadalupes are typified by deep canyons that cut suddenly through the
face of an escarpment and open abruptly into flat plains or a flat
valley floor paralleling the escarpment. As the highly energetic flood
waters rush from the confines of the canyon and spread onto the flats
beyond the canyon mouth, they slow and suddenly lose energy. As a result
of this lost energy, the sediments carried by the flood begin to be
deposited rapidly. A large, cone-shaped pile of flood debris and
sediment called an *alluvial fan* is found at the mouth of canyons like
those seen in the Guadalupe Mountains. Often, inactive areas of the fan
will be overgrown with vegetation typical of the desert and canyon
bottoms. However, arroyos leading from the canyon mouth will cut through
these areas leading floodwaters and sediments to the areas of the fan
where active deposition occurs.

**Materials**

-   vinyl rain gutter cut in 2-foot sections

-   endcaps for rain gutter -- one per rain gutter section

-   sand or dirt

-   rocks -- 1 or 2 inch diameter

-   water source -- 1-liter bottles with sport top and a refill source
    works great!

**Procedure**

***Warm up:*** Ask students if any have ever seen a flash flood. Have
students describe the effects of the flood that they observed during and
after. Have them describe changes made in the landscape and on roadways
and any sediment deposits they noticed.

Discuss the role that periodic flash flooding plays in shaping the
landscape in and near Carlsbad Caverns National Park. Describe the
various features associated with moving water.

***Activity***

1.  Using 2-foot sections of vinyl rain gutter, prepare stream/canyon
    models as shown.

![](media/image8.wmf)

2.  Fill each gutter with dirt approximately 2/3 full at the gutter end
    and slope to where dirt ends about 2/3 of the distance to the end
    (see drawing). The dirt can be packed some and sculpted so that the
    middle section is [slightly]{.underline} lower than the edges. Place
    a rock on the dirt at the upper end. Water will be poured on this
    rock. If they wish, allow students to build small villages with
    "Monopoly" houses.

3.  Be sure to do this part of the activity in an outside location where
    water and mud will not create a problem for others. Set the canyon
    model at a slope with the capped end three to four inches higher
    than the lower end. After this point, students should be instructed
    that they are ***[not]{.underline}*** to touch or manipulate the
    dirt any further. From this point on, only the water will be allowed
    to do that work.

4.  Instruct (and model) students to [gently]{.underline} pour water on
    the rock and let it flow out the mouth of the canyon. This may take
    a few minutes since the dirt will absorb much of the water
    initially.

5.  Once a stream begins to flow the length of the canyon, students are
    to stop and sketch the canyon, being sure to show where various
    features such as arroyos, falls, and bar deposits are forming.

6.  Instruct students to continue gently pouring water to simulate
    periodic flash floods and stopping every three or four minutes to
    draw a new sketch, paying close attention to changes along the
    canyon.

7.  Tell students to pay particular attention to deposits in, or near,
    the canyon mouth. Point out the alluvial fans that begin to develop
    just outside the canyon mouth. Instruct students to include these in
    their sketches.

8.  Clean up the mess.

***Wrap Up:*** Discuss the features students saw develop in their
canyons. Ask if any have seen similar features in real life.

**Assessment**

Collect sketches. Have students:

-   describe the various landforms and deposits associated with moving
    water.

**Extensions**

Have students:

-   study the effect of slope on runoff and erosion by tilting the
    canyon models at several different heights.

-   study the effect of vegetation on erosion by mixing grass in with
    the dirt.

-   vary the intensity of water flow as a study on the effect of water
    speed on erosion.

**Resources**

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

VanCleave, Janice. 1991. *Janice VanCleave's Earth Science For Every
Kid.* New York, NY, John Wiley & Sons, Inc.

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

**Natural Acids**

***What makes those big holes in the ground?***

**Summary:** Students will describe the source of various acids that
form caves and will model the effect of acids on carbonate rocks.

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

**Setting:** Classroom or lab

**Vocabulary:** acid, infiltration, karst, resurging streams, sinkholes,
sinking streams

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

**Objectives**

Students will:

-   describe the sources of two cave forming acids.

-   model the effect of acids on carbonate rocks.

**Background**

![](media/image9.wmf){width="1.0729166666666667in"
height="1.4895833333333333in"}Natural formed acids weather rocks. The
lesson *Stinky Gas and Alabaster* described the processes by which
sulfuric acid from below can form caves like those in Carlsbad Caverns
National Park. However, a different process forms most caves in
carbonate rocks. Groundwater contains carbonic acid, the same weak
*acid* that gives sodas their fizz, and can dissolve carbonate rocks
like limestone. In arid regions, such as those in the desert southwest,
insufficient rainfall prevents this from becoming a dominant cave
forming process. However, in the eastern United States this process
forms most caves. The longest cave system in the world, the Mammoth Cave
-- Flint Ridge system, was formed as mildly acidic groundwater dissolved
a series of large, underground river passages beneath the sinkhole plain
of southwestern Kentucky.

As rainwater falls, it absorbs some carbon dioxide from the surrounding
air. However, most of the carbon dioxide in the groundwater comes from
the soil the water passes through as it *infiltrates*, or sinks into the
ground. As the groundwater moves through cracks, or joints, in the
limestone bedrock it begins to slowly dissolve the rock. The chemical
reactions involved in this process are shown below.

carbon dioxide water

CO~2\ +~ H~2~O

> calcium bicarbonate
>
> carbonic acid calcite solution

H~2~CO~3~ + CaCO~3~ Ca^2+^ + 2HCO~3~^1-^

The rivers formed by this mildly acidic groundwater will flow gradually
downhill until reaching a base water table or reemerging onto the
surface as a spring. In Mammoth Cave National Park, the underground
river eventually flows into the Green River, the base level river for
the area. Cave passages in Mammoth Cave National Park have been formed
on several levels. Older cave passages are located higher, corresponding
to a time when they emerged into a shallower Green River Valley. As the
Green River cut deeper into the valley floor, the underground rivers
feeding into it cut deeper into the beds of limestone, creating newer,
lower passages.

The dissolution of soluble rocks results in a number of surface features
collectively classified as *karst*. Among these landforms are *sinking
streams, resurging streams, sinkholes,* and cave entrances*.* Kars*t*
terrains cover about 12% of the earth's dry, ice-free surfaces. It is
estimated that 25% of the world's population relies on karst aquifers to
supply their water needs. As the joints in the limestone bedrock are
enlarged, the rate of infiltration from above will increase. Eventually,
the flow of water will enlarge the joint to the point that it can be
considered a cave passage. Surface streams channeled into these caves
are called sinking streams. The point at which these streams eventually
resurface is called a karst spring or a resurging stream.

Bowling Green, Kentucky, is located on a plain dotted with so many
dimples that it resembles the surface of a golf ball. In fact, it is
referred to as the "sinkhole plain." A similar sinkhole marked plain
extends from near Santa Rosa, New Mexico into Culberson County, Texas.
Both of these plains are formed by a similar mechanism, the dissolution
of soluble rocks. In Kentucky, the rock type is limestone. In New
Mexico, the soluble rock is gypsum. As the rock dissolves and forms a
cave passage, it weakens the support for overlying rock and soil. If
enough rock is dissolved, the passage can begin to collapse. This
collapse can continue upward until it reaches the surface. The result
can be a collapsed cave entrance or just a closed depression in the
surface.

![](media/image10.wmf)

**Materials**

-   white chalk (broken into 1cm pieces)

-   100 ml beakers or 8 oz. plastic cups

-   water

-   white vinegar

-   safety goggles

-   piece of limestone

**Procedure**

***Warm up:*** Ask students what a large field or meadow would look like
if the bedrock underneath it began to dissolve. Discuss the ideas
presented.

Explain to students that the very thing they just discussed happens in
many parts of the world. Describe and discuss the weathering of
carbonate rocks by acidic groundwater.

Describe landforms that result from the dissolution of soluble rocks.

***Activity***

1.  Provide students with safety goggles.

2.  Place 100 ml water in one of the beakers or plastic cups.

3.  Place 100 ml vinegar in another beaker or cup.

4.  Give each group of students two pieces of chalk. Have them place one
    in the water and the other in the vinegar and record their
    observations.

***Wrap Up:*** Explain to the students that chalk is a type of limestone
made of the shells of tiny animals.

Show the class a piece of limestone. Have them list similarities and
differences between chalk and limestone. Be sure to point out that they
are chemically similar. Ask the students what they would expect to
happen if the limestone was exposed to a weak acid like vinegar.

Review the manner in which caves form as soluble rocks are dissolved by
mildly acidic groundwater.

**Assessment**

Have students

-   describe what happens to limestone when it is exposed to acidic
    groundwater.

-   describe surface features found in areas underlain by soluble
    bedrock.

**Extensions**

Have students research pollution problems found in karst aquifers.
Examples of aquifers include those found in the karst areas of the
eastern US (Kentucky, Tennessee, northwest Georgia, northeast Alabama,
Missouri and Florida would be good places to start). Also, the Edwards
Aquifer of central Texas would be a good topic of study. Have them
describe the most common sources of pollution, research methods, and
activities being done to slow or prevent pollution.

Have the students study the effects of temperature, chalk size, and
concentration of acid on the rate at which the chalk dissolves.

Conduct the same experiment using chips of limestone.

**Resources**

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

Moore, G.W., and Sullivan, G.N. 1978. *Speleology: The Study of Caves.*
Teaneck, NJ: Zephyrus Press, Inc.

VanCleave, Janice. 1991. *Janice VanCleave's Earth Science For Every
Kid.* New York, NY, John Wiley & Sons, Inc.