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THEME: Fires will not burn unless specific conditions exist.
SUBJECTS: General Science, Chemistry, Physics
WHEN: Before your Expedition
OBJECTIVE: Students will learn to recognize and identify the conditions necessary for burning.
METHOD: In small groups, students will attempt to burn a variety of fuel types.
BACKGROUND: Fires need heat, fuel, and oxygen to burn. Remove any of these elements, and a fire will go out. In the northern Rockies, lightning provides a ready source of ignition. Fuels in the form of dead and down trees accumulate at a steady rate because the process of decay is slow in this region. However, conditions in Yellowstone are usually much too cold and wet to achieve large-scale, sustained burning. The drought of 1988 (conditions unprecedented in the park's 112-year written record) was the key event which turned the tide in favor of burning. Severe drought, accompanied by unusually high winds, fanned the fires to their humbling proportions. In 1988, we witnessed a convergence of conditions which may occur once every 300-400 years. Forest fires burn in a mosaic pattern which is reflective of varying fuel types. Wet meadows and stands of young trees do not burn as readily as old forests with large accumulations of litter.
MATERIALS: Matches (enough for five per group), five buckets or boxes containing varying fuel types (keep the amount of fuel in each bucket small).
Bucket #1: A good assortment of sizes of fuels, some with needles, all green.
Bucket #2: Same as #1, but fuels should be dead and dry.
Bucket #3: Same as #2, but fuels should be damp.
Bucket #4: A good assortment of fuels, all partially burned.
Bucket #5: An assortment of fuels, all of a large diameter (small surface area to volume ratio–i.e., no kindling).
Plastic one-gallon containers filled with water, one for each fire.
PROCEDURE: Begin with a discussion of how a fire gets started and whether it is easy or difficult to start one. Instruct the students that they will be trying to start fires in small groups. It may not be easy! The groups must plan their strategies carefully. They will then try to get as much of their fuel to burn as possible in the allotted time. Read them the following rules:
After all groups have had ample time (10 minutes should be adequate), call it quits and assemble groups for discussion. Which groups were successful? Why or why not? Visit each fire site and examine differences in fuel types and success of burning. Do these differences in fuel type occur naturally? Where and under what conditions can each be found? Discuss the extreme fire conditions of 1988, and ask kids to hypothesize as to whether or not it could happen again. What other factors besides fuel type come into play? Point out strategies observed, such as blowing on fires. Introduce a fire triangle model. Demonstrate that if any part is removed, the triangle will collapse and the fire will go out.
EXTENSION: Demonstrate burning in a bell jar:
After having kids hypothesize how it will burn, burn a glass-encased soil profile. Measure the depth of soil charring. Have them tell you why it didn't burn deeper. Discuss the likely vegetative response. On your expedition, hike to see the vegetative response in a burned area.
Hike to observe a mosaic burn. Hypothesize as to why certain areas did not burn (differing fuel types, moisture content, age of trees, etc.). Point out the value of maintaining a vegetative mosaic.
EVALUATION: Have the kids draw and label a fire triangle.
Grades: 4-8
Duration: 30-50 minutes
Group Size: any
Setting: outdoors, preferably in an open area away from buildings or other flammable
objects
Key Vocabulary: hypothesize, litter, mosiac