Subject

• Identify the course of the Firehole River on a map of Yellowstone National Park and list, in writing, at least two locations through which the river passes.
• List, in writing, at least two ways in which the river might be affected when it flows through the park’s geyser basins.
• Participate in a demonstration of a geyser eruption.
• Examine and measure changes in the temperature and acidity of a water sample when infusions of water and baking soda are added.
• Calculate with 100% accuracy the conversion of at least 2 temperatures from Fahrenheit to Celsius, or vice versa.

Materials
Attachment A - Map of Yellowstone National Park (1.4MB pdf)
Attachment B - Firehole in the Classroom Worksheet (13KB pdf)

Glass container able to tolerate hot water
1 cup and ¼ cup measuring cups
Cold water (for best results, refrigerate night before)
Hot water (may be heated in an electric teapot or hot plate or previously
warmed and stored in a thermos)
Baking soda
Spoon
Thermometer (preferably one in which temperature can be measured in both
Fahrenheit and Celsius)
Film canister with small hole punched in the canister’s lid
Antacid tablet such as Alka Seltzer
Litmus paper with pH chart


Background
During this lesson plan, students should practice converting temperature readings from Fahrenheit to Celsius or vice versa.
To convert a Fahrenheit temperature into Celsius:
      A) Subtract 32 from the Fahrenheit temperature
      B) Divide the answer of Step A by 9
      C) Multiply the answer of Step B by 5
Or: TempC=(TempF-32) x 5/9

To convert a Celsius temperature into Fahrenheit:
      A) Multiply the Celsius temperature by 9
      B) Divide the answer of Step A by 5
      C) Add 32 to the answer of Step B
Or: TempF=(9/5 x TempC)+32

The Firehole River begins at tiny Madison Lake in the southwestern corner of Yellowstone National Park, and flows down the north-facing slopes of the continental divide. During the first ten miles of its course, the Firehole River has a temperature of approximately 54°F (12°C) and a pH of 7.4, readings which are consistent with the temperature and pH of many other natural Rocky Mountain streams.

The character of the river changes dramatically when it passes through 3 major geyser basins: the Upper Geyser Basin, Midway Geyser Basin, and the Lower Geyser Basin. By the time the river has completed the 16 mile stretch between the Upper Geyser Basin and Madison Junction, nearly a quarter of its water comes from hydrothermal sources. The river’s temperature increases to a maximum of 79°F (26°C). Its pH increases to 8.3, mainly because of the large amounts of bicarbonate received from hydrothermal runoff.

Much of the water in Yellowstone’s hydrothermal features begins as rain or snow. Precipitation seeps into the ground and then rises back up as it flows through the plumbing system of the feature—a round trip which may take hundreds, or even thousands, of years. In the case of a geyser, the water encounters volcanic rocks underlying the geyser basin, and becomes superheated. An eruption is triggered when this water fills the geyser’s plumbing system and the geyser begins to act like a pressure cooker. Within a geyser’s plumbing system, much of the water can reach temperatures greater than 400°F (205°C) and still remain in a liquid state due to the great pressure exerted by overlying surface water and rock.

As more hot water continues to enter the geyser’s plumbing at depth, the water temperature climbs high enough to overcome the pressure. Some of the water converts to steam. As the steam bubbles become larger and more plentiful, they can no longer rise freely past constrictions or narrow places in the geyser’s plumbing system. Temperatures build and the boiling becomes more turbulent. Eventually the violent bubbling forces some water through the constriction. This release creates an instant reduction in pressure. Much of the water in the system flashes instantly into steam and forcibly ejects the remaining water.

The hydrothermal water carries chemicals, elements, minerals, and bits of dissolved rock which drop out of solution to coat the surrounding landscape or to be carried into streams, such as the Firehole River, by the thermal runoff.


Procedure
The instructor will:

1. Refrigerate at least one quart of water the evening before the lesson.
2. Heat water to boiling using an electric teapot, hot plate, or prepare earlier and store in a thermos.
3. Review the course of the Firehole River with students, using Attachment A or another map of Yellowstone National Park.
4. Hand out copies of Attachment B to students.
5. Instruct students to fill out Attachment B during the course of this lesson.
6. Remind students that the Firehole River passes through 3 major geyser basins in Yellowstone National Park.
7. Review the workings of a geyser with students, as discussed in the Background section.
8. Demonstrate an eruption using a film canister.

      a. Punch a hole into the lid of the canister with a ball point pen and tell students that the hole represents the constriction or narrow place in the geyser’s pluming system.
      b. Fill the canister almost (more than ¾ full) to the top with room temperature water.
      c. Drop 1/2 of an antacid tablet into the water and seal with the punctured lid.
      d. Cover the puncture with thumb and shake once, then uncover.

9. When the “geyser” erupts, ask students to observe where the water lands and to extrapolate where the water might spread when expelled from a real thermal feature in Yellowstone.
10. Ask students how the Firehole River might be affected by thermal infusions.
11. Write the formulas for converting temperatures from Fahrenheit to Celsius, and vice versa, on a blackboard and review with students.
12. Select a student to measure ¾ cup cold water and pour it into the heat- tolerant glass container.
13. Select a student to take a temperature reading of the cold water and announce the result to the class.
14. Instruct students to convert the water’s temperature from degrees Fahrenheit to degrees Celsius on their worksheets.
15. Remind students that by the end of its run through the geyser basins, nearly a quarter of the water in the Firehole River comes from the runoff of geysers and hot springs
16. Select a student to measure ¼ cup hot water and pour it into the cold water in the heat-tolerant glass container.
17. Select a student to take another temperature reading of the water and announce the result to the class.
18. Instruct students to convert the water’s temperature from Celsius to Fahrenheit on their worksheets.
19. Remind students that thermal water also contains chemicals, minerals, and elements from its passage through an underground plumbing system. When thermal runoff enters a stream, the pH and water chemistry of the stream may change, depending on the character of the thermal features that supply water. In the case of the Firehole River, added bicarbonates make the river’s water more alkaline (basic), though other thermally influenced streams in Yellowstone become more acidic.
20. Select a student to use litmus paper to take a pH reading of the water and announce the result to the class.
21. Select a student to add ¼ cup baking soda (an alkaline substance) into the water and stir with spoon until it is thoroughly mixed.*
22. Select a student to take another pH reading and announce the result to the class.
    
    * The instructor may want to repeat the experiment using an acidic substance such as vinegar or lemon juice for comparison.