A Geological Phenomenon
National Park Service Mission
...to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations.
Black Canyon of the Gunnison National Park and Curecanti National Recreation Area Outreach Education is committed to: Creating an awareness and fostering an appreciation for the mission of the National Park Service and the natural, cultural, and historic resources of Curecanti National Recreation Area and Black Canyon of the Gunnison National Park.
EDUCATION LESSON PLAN
Title: A Geological Phenomenon
Colorado Content Standards:Science: (2.1) Students know that matter has characteristic properties, which are related to its composition and structure. (4.1) Students know and understand the composition of Earth, its history, and the natural processes that shape it. (5) Students know and understand interrelationships among science, technology, and human activity and how they can affect the world.
III. TEACHING PROCEDURE/METHODOLOGY
At The Visitor Center (or At North Rim Campground)
Discuss safety/rules. A Ranger should lead the students to and from each of the overlooks, to avoid anyone getting lost as there are multiple paths at some of the overlooks. Walk, do not run. Treat the field trip as if in an "outdoor classroom". Take turns listening, raise hands to answer questions and keep talking to a minimum so that all the other visitors can enjoy the overlooks. Do not throw ANYTHING over the edge. A small pebble will reach speeds like a bullet from a gun as it nears the bottom of the canyon. A small rock could trigger larger rocks to slide, potentially injuring hikers and rock-climbers below. Make sure sunglasses, hats, water bottles, etc. are secure because if they accidentally drop over the edge no one will be retrieving them. Do not climb on any of the fences or barriers at the overlooks. Do not take any rocks, flowers, etc., from the park. Not only are there fines for this but others will not be able to enjoy the same things that you will be seeing today.
Let students know that at each overlook they will be given some time to look around and take pictures and a discussion will follow (approximately 15 minutes long).
Divide the students into two equal groups. One group will walk down to Gunnison Point overlook, and the other group should ride the bus to Warner Point. After dropping the students off at Warner Point, the bus driver will return to the visitor center to transport Group 1 to the Pulpit Rock overlook. Bus driver will wait there until the activity finishes, at which point he’ll drive Group 1 to Warner Point. Both groups will eat lunch at the Warner Point picnic area and then flip-flop activities.
Gunnison Point (depth from rim 1,840 ft.)*** (or at Balanced Rock, on North Rim)
Give students a couple of minutes to look at the canyon.
What is Geology? The study of rocks and the earth (its composition and how it changes over time). What do you call a person who studies rocks and the earth? A geologist. How old do Geologists believe the earth to be? 4.6 billion years. Geologists break rocks down into three major categories. Can anyone name one of them? Sedimentary, Igneous and Metamorphic. Does anyone have an idea of how one of these types of rock is formed? Sedimentary rocks are formed from the intense pressure of many layers of sediments (e.g. sand, mud, or silt) piled on top of one another." Have four students stack their hands on top of each other. One student's hands represent sand, the next represents mud, another silt, and the last student represents clay. When compressed over time, they form a solid rock. Have the students gently push their hands together to represent a solid rock. "Examples of sedimentary rocks include sandstone and mudstone. In the Precambrian Era, much of the rock that makes up the canyon walls was sedimentary. However, due to extreme pressure and heat applied to the sedimentary rock underground about 1.7 billion years ago, it became metamorphic rock. Metamorphic rock forms when other rocks (sedimentary or igneous) undergo extreme heat and pressure. An example of a sedimentary rock is limestone. If it undergoes heat and pressure, it will turn into marble, a metamorphic rock. All of the dark-colored parts of the canyon walls are metamorphic rock, mostly consisting of schist and gneiss (nice). Igneous rock also forms a large part of the canyon walls. These rocks are formed from molten or volcanic rock (magma - if it's inside the earth; or lava - when it's expelled from the earth). Can everyone show me how igneous rock is formed?" Demonstrate the sound an action of a volcano and everyone says together, 'IGNEOUS!'. Igneous rocks can be broken down into two sub-categories: intrusive (magma has hardened inside of the earth) and extrusive (lava has hardened outside of the earth). Examples of extrusive igneous rock that are commonly found on the tops of mesas in this area are: Welded Tuff (ash from the San Juans to the South) and Breccia (mudflows from the West Elks to the North). An example of intrusive igneous rock is the pink colored rock underneath our feet right now. We can also see examples of this pink rock, called pegmatite, on the canyon wall across from us. Approximately 1 billion years ago, molten rock squeezed its way between cracks in the metamorphic rock and eventually hardened there." Show example of goo being squeezed into the crevices of a rock, wood, plastic object, etc. "Pegmatite is composed of the minerals feldspar, mica and quartz. Across from where you're standing you can also see pegmatite "dikes" which look like fins sticking out of the canyon walls. The reason these formations exist is because pegmatite is more resistant to erosion than the schist and gneiss surrounding it and therefore remains after the other rock is eroded away." Cover the plastic funnel with wet sand. Have one student blow on it and another student spray water on it to demonstrate erosion. Compare the hard plastic funnel to the pegmatite dikes. Let students know that you will discuss erosion in more detail at the next overlook. "Keep in mind that rocks are continually being altered, in a cyclic pattern. In other words, under the right conditions, sedimentary rock could be changed into metamorphic rock (heat and pressure), metamorphic to igneous (volcanic action), igneous to sedimentary (erosion producing layers of sediment). We call this process the rock cycle.”
Have students get into two lines to get on the bus. The Ranger can then quiz each pair of students with questions while they get on the bus.
Pulpit Rock Overlook (depth from rim 1,770 ft.) (or at Kneeling Camel overlook on North Rim)
Give the students a couple of minutes to look at the canyon. Point out the South Rim VC/Gunnison Point Overlook, etc.
Let’s go WAY back in time and discuss how the Black Canyon was formed. You’re all actually going to get the chance to act out the geologic history of the area, so I’m going to need 10 volunteers to come up and help me. (Have 8 students come up and stand in front of the class. This is for a class of 20. If there are more or less, the number of volunteers being the basement rock is variable).
The rock that you see forming the walls of the canyon is considered by geologists to be some of the oldest rock in the world and is called basement rock. Now, my 10 volunteers are going to be the basement rock in this canyon. It used to be buried underground, far below sea level, in the form of a sedimentary rock (have students crouch down). What do we know about sedimentary rocks? That’s right! They have layers. I need all of my basement rock to show me their layers (Have students place arms horizontally in front of themselves like layers). Approximately 1.7 billion years ago extreme heat and pressure metamorphosed the basement rock into metamorphic rock (Have students “deform” their layers by bending their arms). Who can remember what causes a sedimentary rock to become a metamorphic rock? That’s right, heat and pressure.
From approximately 1.7 – 1.4 billion years ago, magma intruded into the basement rock and cooled to form intrusive igneous rocks. I’m going to need 2 volunteers who can come up and be our igneous intrusions. (One volunteer will be a massive granitic intrusion, so they can form a hoop with their arms and “push” some of the basement rock out of the way. The other can be the pegmatites and snake their way into the middle.)
Around 60 million years ago there was movement along some fault lines in this area that pushed a block of ancient, hard rock upward (Have basement rock students stand up). This 65 mile stretch of land that was uplifted is called the Gunnison Uplift, 14 miles of which is located within the boundaries of this National Park. After this area was uplifted, it was leveled out by the forces of erosion. Can I have two volunteers to be my forces of erosion? (Have one student be wind and blow on the Uplift and have the other squirt them with a water bottle.) The sediment created by the erosion buried part of the uplift under a river plain. Now I need volunteers to be the San Juan and West Elk Mountains. About 30 million years ago, the San Juan and West Elk Mountains erupted, spreading ash and volcanic material all over this area (have 4 volunteers pretend to be erupting volcanoes, 2 standing to the north as the West Elks and 2 standing to the south as the San Juans). These eruptions determined the present-day course of the Gunnison River. The ancient river was able to cut easily through the soft volcanic rocks, carving a deep channel. So by the time the Gunnison River had reached the hard metamorphic rocks below (2 Mya), it had become trapped in its present day course and was forced to continue to cut away at the hard basement rock. (Have remaining students form a line and hold hands to carve a canyon through the middle of the basement rock.) Up until the damming of the Gunnison River, it was carving the canyon at the rate of 1 inch per century, or the width of a hair per year. The canyon walls were formed by the friction of water on the rock and also the rocks and sediments that scraped the rock walls as they were pushed down-river by the fast flowing water.
Do you think that the Gunnison River flowed faster or slower before the Blue Mesa, Morrow Point, and Crystal dams were built on it? Faster. Before being dammed, the river could reach a peak flow almost 30 times faster than its current average flow (450 cfs vs. 12000 cfs). Therefore, do you think that the river water is cutting through the rock faster or slower than before? Slower, because less water is flowing and causing erosion. However, there are still many other forces besides the river that continue to erode the canyon walls- can anyone think of any? Wind and water often carry sediments which help to wear away rock. Another process that can cause erosion is mechanical. If a seed gets deposited into a crack, eventually its roots may develop. What happens as the plant grows? The roots get bigger and force the crack to open wider. Rocks can also be weathered chemically. Chemicals excreted by lichens (lichens = a close association of algae and fungi) dissolve nutrients in the rock's surface. This, too, causes erosion, on a smaller and slower scale. Another erosional force is called freeze-thaw. We can visualize freeze-thaw if we compare it to a glass of water in the freezer. Has anyone ever put a glass of water in the freezer? What happens? The cold temperature causes the glass to crack, and the same thing happens to rock when it gets cold and moist. This freeze thaw cycle happens over and over, causing more cracks in the rocks.
Take a look at the north and south rims (you're standing on the north one). What is the difference? The north one is almost a vertical drop, while the south side is a more gradual slope down toward the river. Does anyone know why it is this way? What happens to snow, ice and rain when the sun strikes it? It evaporates. The north rim receives more winter sunlight than the south rim (because of the sun's position). Therefore, the precipitation evaporates quickly, causing little freeze-thaw erosion in these rocks. Due to the fact that the south rim receives considerably less sun in the winter, it has been eroded by freeze-thaw action for millions of years. Since there is less direct sunlight and less evaporation, this means that there is more moisture left on the south side. Where do plants grow better, in a wet area, or in a dry area? Right, plants need plenty of water to grow. The moisture provides better conditions for plant growth. Therefore, erosion caused by the growth of the plants' roots further contributes to the more gradual slope of the canyon walls seen on the south rim."
Walking Guide for Ranger (for the South Rim…North Rim has a different worksheet)
At beginning of trail, bend over and “pick up” a folded paper (the top secret riddle) that says, “Top Secret” on it in red writing. Hold it up for all the kids to see, and ask them if they think we should open it. (They’ll all say yes!) Read it out loud in a dramatic tone of voice, and ask the kids if they are ready to tackle the riddle of the rock breaker. (They’ll all be very excited). Let them know that we’ll stop 6 times along the ½ mile trail, where we’ll look for clues to help us solve the riddle. The ranger should always be the leader. Hand out a worksheet for each student to work on along the way. Bring pencils for the kids to use or share.
Stop 1, just after post 2
Geology-look around, be observant, what do you see?
Sagebrush-12x the fat content of alfalfa (deer rely on it during the winter)
Juniper-tolerate drought by isolating a limb
Pinyon evolved 30 million years ago
But look underneath your feet, too. (Rocks and soil!) Could the plants live without the soil? No. Could the animals live without the plants? No. Therefore, Everything depends on the rocks beneath our feet, the geology.
Stop 2, at post #4
Igneous-Single out the San Juan Mountains-they are volcanic. How did they get there? Tie in igneous rock, and explosive volcanoes. There are two kinds of volcanoes: those that are active that go glub, glub, glub and lava slowly pours out; explosive volcanoes, where rock and ash explode out. Where does the ash go? It falls like snow all over the place. The lava and rocks become igneous rock. All igneous rock was once liquid.
Stop 3, down the steps, under the pinyon trees
Mancos- Focus on the mancos Shale. Ask the kids what they know about the ‘dobes. Describe sedimentary rock again for them, and why this layer is different. What is all that grey/brown rock down there? Review how each type of rock is formed. This is sedimentary rock. Why is Flattop flat? Flattop has a layer of hard rock on top. What is it called when rocks break down? Erosion. What causes erosion? Rain, wind, water, etc. The hard rock on top of Flattop does not erode very easily, so it protects the softer rock beneath it.
Stop 4, after post #5
Hardness-rocks are made of different minerals cemented together. Draw analogies between mineral formations, and things they understand. Sometimes minerals=gemstones. How do we identify minerals? Hold up several different mineral examples. Ask them what differences they see between the minerals. Geologists perform certain tests, to determine the luster (shininess), color, weight, magnetism, and hardness to tell one mineral from another. We measure the hardness of minerals by scratching them against various items. For instance, if we can scratch our fingernail with the mineral, we say it’s harder than 2.5 on the hardness scale. If we can scratch glass, then it’s harder then 5. If a steel file doesn’t scratch it, then it’s harder than 7.5. A diamond has a score of 10 on the hardness scale. What’s the hardest mineral? Diamond.
What’s the mineral that looks like gold, but really isn’t? It’s called pyrite, or fool’s gold! Can you look around and find a shiny mineral called muscovite mica?
Stop 5, at post #6
Metamorphic- You’ll have a great view of the canyon and the valley from here. You can address erosional geology, including river cutting (contrasting the Gunnison River with the Uncompahgre River), and including erosional remnants like the mesas across the canyon and Flat Top Mesa near Montrose.
You can address how magma moves below the surface and contrast the Vernal Mesa Quartz Monzonite that is abundant at this stop with the pegmatite that you saw at the last stop.
You can also address the concept of the Gunnison Uplift and of geologic time through uplift, erosion, rock formation and so on.
Stop 6, just after post #6, or up the hill
Warner - reverend from Montrose, worked with Congress to get the area recognized and protected. Who was the president who designated it a national park? Bill Clinton, in 1999.
After stop #6, ask the kids if they’ve solved the riddle. When they say lichen, ask them if they know what lichen is, and if they can find an example. Explain that lichen is a symbiotic relationship between an algae and a fungus (lichen is not a plant!). The algae is green (as you may have noticed if you haven’t cleaned your fishtank in awhile) and can use sunlight to photosynthesize, or produce its own food. The fungus can’t produce its food, so it relies on the algae for food, but it can provide shelter and hold the algae onto the rock. They benefit each other. Hold up the example and ask if this tiny organism can climb walls. Yes, because it clings to the rocks and grows in any direction. Is this tiny organism strong enough to break rock down into soil? Yes, because the symbiotic relationship between the algae and the fungus causes an acid to be secreted, which breaks down the rock very, very slowly and turns it into soil. And explain that it’s very sensitive to air pollution. Based on the fact that we found it here, do you think we have clean air at the Black Canyon? Yes! Congratulations on becoming a Geologic Detective!
IV. CHECK FOR STUDENT UNDERSTANDING
IX. REFERENCES CITED
Prather, Thomas. (1982). Geology of the Gunnison Country. Gunnison, Colorado: B & B Printers, Gunnison, Inc.
Houk, Rose. (1991). Black Canyon of the Gunnison. Tucson, Arizona: Southwest Parks & Monuments Association.
Parker, Troy Scott. (1993). South Rim Driving Tour Guide: Black Canyon of the Gunnison National Monument. Tucson, Arizona: Southwest Parks & Monuments.
Did You Know?
To get to the Morrow Point Boat Tour in Curecanti National Recreation Area, visitors must walk down (and back up) 232 stairs on the Pine Creek Trail. More...