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DISCOVERING THE MYSTERIES OFBRYCE CANYON NATIONAL PARK

Objectives:

methOd:

backgrOund:

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.

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.

How do you make a Hoodoo?

Grade Level: 4th-8th grades

Subject Area: Earth Science

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.

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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

DISCOVERING THE MYSTERIES OFBRYCE CANYON NATIONAL PARK

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.

How do you make a Hoodoo?

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DISCOVERING THE MYSTERIES OFBRYCE CANYON NATIONAL PARK

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

Part 1: Identification of limestoneProcedure:

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

activity:

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 wedgingProcedure:

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.

How do you make a Hoodoo?

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DISCOVERING THE MYSTERIES OFBRYCE CANYON NATIONAL PARK

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.

extensiOn activities:

references:

Bryce Canyon National Park – website:http://www.nps.gov/brca/nature-science/hoodoos.htm

Frost wedging simulation:Judy Breckenridge, Muriel Mandell, An-thony D. Fredricks, and Louis V. Loeschnig: 365 Super Science Experiments With Everyday Materials (2001).

Part 3: Simulating hoodoo formationProcedure:

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.

How do you make a Hoodoo?

The National Park Foundation is the national charitable partner of the National Park Service.