bryce canyon national park

DISCOVERING THE MYSTERIES OF
BRYCE CANYON NATIONAL PARK
How do you make a Hoodoo?
Grade Level: 4th-8th grades
Subject Area: Earth Science
Objectives:
Introduce and describe limestone
Offer an overall explanation to the question of
how hoodoos are formed.
Illustrate the stages that rocks go through during
hoodoo formation (plateau, fin, window, hoodoo).
Show that the rock formations at Bryce Canyon
erode rapidly because of frost wedging.
method:
Students will learn how to identify limestone in
a hands-on experiment. Students will make observations of a
demonstration simulating frost wedging.
Students will simulate hoodoo formation by
coating sugar cubes with a salt clay slurry (or
plaster of Paris).
Students will compare their hoodoos to images of
Bryce Canyon hoodoos and name their hoodoos.
background:
Rocks are composed of one or more minerals.
Minerals are naturally occurring elements (gold) or
inorganic compounds (quartz). Each mineral is a
naturally occurring, inorganic solid with a specific
crystal structure and chemical composition. There are three major categories of rocks: igneous,
sedimentary, and metamorphic. Igneous rocks
form from molten rock (magma) that has cooled.
Examples are granite, basalt and pumice. Igneous
rocks that cool slowly beneath the Earth’s surface
usually contain large interlocking crystals. Igneous
rocks that are created in volcanic eruptions have
smaller crystals or may be glassy in texture. Detrital
or clastic sedimentary rocks form when sediments
are deposited by water or wind on the surface of
the earth, they are lithified over time, as the
sediment grains are cemented together to form
rock. Other sedimentary rocks form by chemical
processes. Sedimentary rocks are commonly layered,
a result of the way their sediments that make them
up are deposited. Metamorphic rocks can begin
as any rock type but they are altered (not melted) by
heat, pressure and/or chemically active fluids. Some
examples are: sandstone which metamorphoses
into quartzite, limestone with metamorphoses into
marble, and granite which metamorphoses into
gneiss. Crystals commonly seen in metamorphic
rocks are usually oriented in lines or sheets called
foliation.
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DISCOVERING THE MYSTERIES OF
BRYCE CANYON NATIONAL PARK
How do you make a Hoodoo?
introduction:
Most visitors that come to Bryce Canyon National
Park become quite familiar with the Claron
Formation. The pink cliffs and thousands of rock
spires or hoodoos found down to 800 feet
beneath the plateau rim are carved from rocks in
the Claron Formation. Sediments that make up the
Claron Formation were deposited beginning about
60 million years ago when fresh water lakes filled
shallow basins in what is now Southern Utah. A
hoodoo is a rock feature that is created by water,
weather and wind over a long period of time.
What makes the HOODOOS? A process called frost
wedging, where the water freezing (expanding)
and thawing (contracting) in pores and cracks,
causes the rocks to break apart. Beneath the
plateau rim over 200 freeze-thaw days occur in
any given year. At night, as the temperatures dip
below freezing the water that has seeped into
cracks and fractures in the rock freezes. As the
water freezes it expands, by as much as 10%, this
expansion forces the cracks and fractures in the
rock to open wider. As the morning sun warms
the rock layers the water in cracks and fractures in
the rocks melts. This causes the rock to begin to
crumble and erode away. Many hoodoos appear
to be coated in a stucco-like coating of minerals.
This coating forms as a result of the slightly acidic
snow and rain that fall on the rocks of the Claron
Formation. After many years of frost wedging and
acidic precipitation the striking features we know
as hoodoos are formed. Hoodoos that form on
south facing slopes tend to be the most striking.
The hoodoos in Bryce Canyon have different colors
as a result of the different minerals found in the
layers of rock that make them up.
There are four main stages in hoodoo formation
(pictured below).
Just as hoodoos are formed by environmental
conditions of frost wedging and acidic
precipitation, they are quickly eroded away. On
average, hoodoos erode away at a rate of about
2-4 feet per hundred years.
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DISCOVERING THE MYSTERIES OF
BRYCE CANYON NATIONAL PARK
How do you make a Hoodoo?
materials:
Limestone hand samples – one for each
small group of students
Sandstone (or other rock samples – not
limestone) – one for each small group of
students
2 ounces (60 mL) of lemon juice, vinegar
or dilute HCl (10%).
Hand samples of sandstone – small
enough to fit into a zip lock plastic bag
Zip lock plastic bag
Water
Sugar cubes
Salt clay slurry (or slurry of plaster of
Paris)
Food coloring
Images of hoodoos from Bryce Canyon
Plastic cups
Plastic spoons
activity:
Part 1: Identification of limestone
Procedure:
reacts with the alkaline limestone to produce carbon
dioxide, resulting in the appearance of bubbles of
escaping gas. Marble is a rock formed from limestone
and will react with the acid the same way as the
limestone. Similar results will also occur if lemon
juice, vinegar or HCl is poured on chalk, as it is also
made of limestone.
Part 2: Simulating frost wedging
Procedure:
1. Soak small pieces of sandstone in water at least
overnight.
2. Place the pieces of sandstone into zip lock plastic
bags and seal tightly.
3. Place in a freezer at least overnight.
4. Remove from the freezer.
5. Observe and discuss.
Discussion: The sandstone absorbs water into the
pore spaces between the grains of sand that make
up the rock. When the rock is placed in the freezer,
the water freezes and expands. As this happens it
causes the sandstone to crumble because the water
expands wedging apart the sand grains. It may also
be a good idea to experiment with various rock types
in this demonstration in order to learn about the
susceptibility of different rock types to frost wedging.
1. Pour a few drops of the lemon juice, vinegar or
HCl over each of the rock samples.
2. Observe and discuss.
Discussion: Limestone reacts to the acid in lemon
juice, vinegar or HCl by effervescing. Students will
be able observe the limestone being dissolved by the
weak acidic solution as it gives off carbon dioxide
in the form of a gas. Limestone effervesces because
it is composed of calcium carbonate, an alkaline
substance. When the acidic lemon juice, vinegar
or HCl is poured on the surface of the limestone, it
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DISCOVERING THE MYSTERIES OF
BRYCE CANYON NATIONAL PARK
How do you make a Hoodoo?
Part 3: Simulating hoodoo formation
Procedure:
1. Provide students with a set number of sugar cubes
(minimum of 20 per group). Ask students to stack the
sugar cubes into the basic structure they would like
for their hoodoo. (This simulates the fin and window
stages of hoodoo formation.)
2. Using the plastic spoon, drip the colored slurry
over the hoodoo structure so that it runs down the
sides and coats the sugar cubes. (Try leaving streaks
of food coloring in the slurry for a more authentic
effect.)
3. Allow to dry overnight.
4. (You may want to use a drop of Elmer’s glue
between sugar cubes to hold the structure firmly in
place prior to applying the slurry coating.)
5. Observe and discuss.
6. Show student images of Bryce Canyon hoodoos
along with the names given them. Ask students to
name their hoodoos.
Extension activities:
Collect data and calculate the dissolution rate
of limestone. Determine the mass of a piece
of chalk using a balance. Place the chalk into a
beaker containing dilute HCl for a set period of
time, 10 minutes minimum. Remove the chalk
from the acidic solution and dry overnight.
Measure the mass a second time. Use the
decrease in mass and amount of time the chalk
was in the acidic solution to calculate a rate of
dissolution.
Have students research cave formation and
speleothem deposition. Students could collect
images of speleothems and caves and compare /
contrast them to hoodoo images.
references:
Bryce Canyon National Park – website:
http://www.nps.gov/brca/naturescience/hoodoos.htm
Frost wedging simulation:
Judy Breckenridge, Muriel Mandell, Anthony D. Fredricks, and Louis V. Loeschnig:
365 Super Science Experiments With
Everyday Materials (2001).
The National Park Foundation is the national charitable
partner of the National Park Service.
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