Death Valley lies just to the east of the high peaks of the Sierra Nevada Mountains of central California. At 282 feet below sea level, it is the lowest point in the United States. It is also both the hottest and driest place in the United States. Death Valley is an example of a “rain shadow desert,” one of many such deserts located in the lee of high mountain ranges around the world. This lesson will help students to evaluate how the interactions of air, moisture, wind, and topography combine to create an environment of such extremes.
Utilizing a directed inquiry approach, students will discover precipitation patterns in the southwestUnited States. Using segments from the Nature episode “Life in Death Valley,” precipitation maps and GoogleMaps satellite images (or an optional Google Earth tour) students will describe the differences in precipitation on the west and east flanks of the Sierra Nevada.Through classroom discussion, students will then explore the reasons for those differences.
Students will be able to:
- Read and interpret a Planetary Winds diagram
- Describe the precipitation patterns on the windward and leeward sides of mountains
- Explain the reasons for the precipitation patterns on the windward and leeward sides of mountains
- Relate knowledge about temperature and pressure to meteorological effects
Two 45-minute classperiods
For each student:
- A copy of the Planetary Winds diagram from page14 of the Earth Science Reference Tables (ESRT)
- Rainshadow Student Organizer
- Precipitation Student Organizer
For each group of 3-4 students:
For the classroom:
- One computer with broadband internet access, connected to a LCD projector and screen
- One overhead projector or similar digitalprojection device
- Rainshadow Student Organizer - Rainshadow Student Organizer Answer Key
- Precipitation Student Organizer - Precipitation Student Organizer Answer Key
- Optional Google Earth tour to accompany thisclassroom exercise: rainshadow.kmz
- Google Earth Instructions
A diagram from the New York State Education Department’s Earth Science Reference Tables (ESRT).
A color-coded map from the United States Geological Survey showing terrain elevations in California.
A color-coded map from Oregon State University showing average annual rainfall in California.
Before The Lesson
Prior to teaching this lesson, you will need to:
Preview all of the video segments and Web sitesused in the lesson.
Download the video segments used in the lesson toyour classroom computer, or prepare to watch them using your classroom's Internetconnection.
Bookmark the Web sites used in the lesson oneach computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo(or an online bookmarking utility such as portaportal)will allow you to organize all the links in a central location.
Make copies of all print materials as outlinedin the materials section. Make sure you can quickly and reliably switch thescreen from the computer display to the overhead or digital projection display.If using the optional Google Earth Instructions followadditional instructions.
Part I: Introductory Activity
1. Introduce students to Death Valley by explaining that it is located to the east of the high peaks of the Sierra Nevada Mountains of central California. Provide students with a focus for media interaction by asking students to share what they already know about Death Valley and how the characteristics of the landscape effect the climatic conditions of the area. Display the Google Map (or from the satellite view on http://maps.google.com, search for “Death Valley, CA” and zoom out until the Sierra Nevada Mts. are visible on the left side of the screen). Be sure to explain that it is 282 feet below sealevel--the lowest, hottest, and driest place in the United States.
2. Provide students with a focus for media interaction by asking them to describe the climate, weather conditions, and landscape portrayed in the segment. Play You Can Die Here. Lead students in a discussion of the climate, weather conditions and landscape (Possible answers: This is the hottest and driest place in the western hemisphere; there are large salt flats, vast deserts,and deep craters.)
Part II: Learning Activity #1
1. Distribute the Precipitation Student Organizer to each student. Open and display the Google Map (OR from the satellite view on http://maps.google.com,search for “Orange Cove, CA” and zoom in and out in order to be able to see the surrounding landscape). Point out the central valley of California, the Sierra Nevada Mountain range, and the Basin and Range region in nearby Nevada. Provide students with a focus for media interaction by asking them to describe the landscape conditions of each area as seen on the Google map. Be sure to point out the differences between the landscapes on either side of the mountain (see teacher key for answers).
2. Zoom into and browse around the Orange Cove areaon your Google map until you can see the existence of orchards. Provide students with a focus for mediainteraction by asking them to a) describe the type of human activity going on here, and b) describe the surrounding landscape (Section 1 on the Precipitation Student Organizer). Lead adiscussion with the students about their answers and ask them to share how they reached their conclusions (see teacher key for answers).
3. Open and display Google Map (OR from the satellite view on http://maps.google.com,search for “Badger, CA” and zoom in and navigate west in order to be able to see the surrounding landscape). Provide students with a focus for media interaction by asking them to describe the vegetation covering these mountains. What does the presence of this vegetation suggest about the amount of rainfall here? (Section 2 on the Precipitation Student Organizer.) Lead a discussion with the students about their answers (see teacher key for answers).
4. Using the same map used in Step 3, scrollfurther east over the top of the Sierras into the arid basins east of the mountains, and zoom in slightly on the landscape. Provide students with a focus for mediainteraction by asking them how the vegetation here compares to the vegetation at the foothills of the Sierras? What does the landscape suggest about the rainfall (Section3 on the Precipitation Student Organizer)? Lead a discussion with the students about their answers (see teacher key for answers).
5. Project the following two maps:
Optionally, also distribute color copies of each map to the students. Provide students with a focus for media interaction by asking them to compare the areas of high andlow precipitation with the areas of high and low elevation and fill in Section 4 on the Precipitation Student Organizer. Lead a discussion with the students about their answers. Be sure to point out the increase in precipitation that corresponds to an increase in altitude.
6. Project the planetary winds diagram on page 14 of the ESRT. Tell students that the contiguous United States is located between 30 and 45 degrees north latitude. Provide students with a focus for media interaction by asking them to determine which way the wind moves at that latitude and to write their answers in Section 5 of the Precipitation Student Organizer. Lead students in a discussion about their answers (see teacher key for answers).
Part III: Learning Activity #2
1. Display the Rainshadow Student Organizer on an overhead projector. Distribute copies of the organizer to the students. Point out the different areas of the diagram and provide students with a focus for media interaction by asking them to describe the types of landscapes found in each area as previously discussed. Tell students that the main movement and direction of wind over the United States is from west to east, and that these are called prevailing winds. The winds that approach the Sierra Nevada Mountains are called the prevailing southwesterlies due to the fact that they aretraveling from the south west. Draw a few arrows indicating wind direction and label the “Prevailing Southwesterlies” on the Rainshadow Student Organizer. Ask students to duplicate your drawing on their worksheets. Ask students if anyone can define windward (facing into the wind) and leeward (eastern facing slopes). Label area B on the diagram, windward (see figure 1). Label area D on the diagram: leeward (see figure 1).
2. Ask students to speculate what happens to air near the surface of the earth as it is encounters the Sierra Nevada Mountains. Be sure to discuss how it rises up over the windward side of the mountains and sinks back down on the leeward side. Ask students to add a few arrows to indicate the movement of air their worksheet (Figure 2).
3. Ask students to think about and discuss the nature of the air mass at point A, particularly with respect to temperature and moisture content, as it comes from over the Pacific Ocean. Explain how this maritime tropical air mass is warm and moist due to the fact that it is coming from the subtropics and travels a long distance over the water. Askstudents to write “warm moist air” next to point A on the diagram (Figure 3).
4. Ask students to predict what topographical features might influence cloud formation. Discuss these predictions. Provide students with a focus for media interaction, asking them over what topographic features do the clouds form, and where do they seem to dissipate? (Section 6 on thePrecipitation Student Organizer.) Play Clouds and Currents. Explain how storm clouds from the south west are formed over the mountain peaks due to the warm air that cools and expands as it rises over the mountain. This cooling and expanding causes the condensationof water vapor in the air. Ask the students to draw a rain cloud in area C on their diagram (Figure 4). Lead a discussion with the students about their answers in Section 6 of the student organizer, making sure to incorporate the definition of a rainshadow (the dry area on the leeward side of a mountain).
5. Explain to the students that the condensation that occurs over the mountain peak releases latent heat (energy stored in the water vapor) at evaporation. This releases measurable, sensible heat back into theenvironment, keeping the rising air warmer than dry air that has risen to the same altitude. This process adds to the warming effect on the leeward side of the mountains. The air then continues down the leeward side of the mountain. The pressure increases as the air descends and results in further warming. The end result is the extremely hot, dry air found in Death Valley. Ask students to add the label “Hot Dry Air” to their diagram (figure 5).
6. Below the rainshadow desert diagram, there are fivestatements referencing the different areas in the diagram. Ask the students to match the appropriate description with its corresponding area (area A, area B, area C, area D or Death Valley) as it appears on the bottom of their rainshadow desert diagram. Lead students in a discussion about their answers (see Rainshadow Student Organizer Answer Key for answers).
7. Provide students with a focus for media interaction, asking them to describe the conditions in Death Valley, especially in terms of moisture evaporation rates andtemperature and record their answers on Section 7 of the Precipitation Student Organizer. Play Runnin' with the Devil. Lead students in a discussion about their answers (see teacher key for answers). Ask the students if they’d like to visit Death Valley and why .
Using the USGS website listed in the CulminatingActivity, guide students to the information pertaining to desertification. Provide students with a focus for media interaction – Ask students to read the information regarding desertification. Lead a discussion with the students about the dangers of desertification (the “degradation of formerly productive land”) and some potential remedies.
Using a CO2 fire extinguisher, demonstrate the cooling thatoccurs when gas expands. Explain to studentsthat the CO2 inside the fire extinguisher is under great pressure. Ask students to predict what they think willhappen to CO2 gas as it exits the container. Spray a piece of fabric with the fire extinguisher. The escaping CO2 will solidify and form iceyresidue on the material demonstrating the cooling that occurs as the escapinggas expands.
Have students research how different cultures haveadapted to life in deserts. Possible subjects could include nomadic Bedouins and southwestern Native Americans.
Ask students to research and report on the meteorologicalconditions of their local area, and how they are affected by geographical features.
Invite a local nursery to make a classroom presentation about the needs of desert-habitat plants. Ask any students who have such plants at home to bring them in to share with the class.
Invite a local pet store to make a classroom presentationabout the needs of desert-habitat animals. Ask any students who have such pets at home to bring them in to share with the class.