Last updated: July 28, 2015
- Grade Level:
- Middle School: Sixth Grade through Eighth Grade
- Lesson Duration:
- 60 Minutes
- Common Core Standards:
- 6-8.RST.1, 6-8.RST.2, 6-8.RST.4, 6-8.RST.8
- State Standards:
- Washington State Science Standard EALR 4 Earth and Space Science - Grades 6-8 Cycles in Earth Systems
- Thinking Skills:
- Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words. Applying: Apply an abstract idea in a concrete situation to solve a problem or relate it to a prior experience. Analyzing: Break down a concept or idea into parts and show the relationships among the parts. Evaluating: Make informed judgements about the value of ideas or materials. Use standards and criteria to support opinions and views.
Students view distribution patterns of tephra layers found around Mount Rainier on an isopach map and discover their source. After this lesson, students will be able to answer the questions:
How was tephra dispersed in the Cascade string of Volcanoes and specifically at Mount Rainier?
Tephra is a general term for fragments of rock and lava regardless of size that are blasted into the air by explosive eruptions. Tephra includes large rocks and small fragments, such as scoria, pumice, and volcanic ash. At Mount Rainier, tephra is conspicuous as a sandy material in colorful shades of orange, tan, yellow, gray, brown, and white. Each tephra layer represents an eruptive event.
During an eruption, large pieces of dense rock, pumice and scoria drop on the slopes of the volcano while volcanic ash often remains aloft and is transported laterally. When volcanic ash and surrounding air cools, and air speed is insufficient to support it, the ash drops to the ground and forms a layer often in the shape of an elongated oval.
While Mount Rainier is the source for at least 40 recognizable tephra layers, not all of the tephra found within Mount Rainier National Park originated there. Wind carried volcanic ash from eruptions at Mount St. Helens to the slopes of Mount Rainier on at least two occasions, once between 3,700 and 3,800 years ago and in A.D. 1480 (layers Yn and W respectively), and from Mount Mazama (Crater Lake) in Oregon to broad regions of the Pacific Northwest around 7,700 years ago (layer O).
These rogue layers puzzled early researchers who found the ash in unexpected locations and who recognized that their chemical composition differed from rocks at Mount Rainier. By carefully mapping the thickness of each ash layer, geologists were able to see that the ash layer thickened away from Mount Rainier and thereby were able to trace the ash and pumice to its source. They confirmed their hypothesis, thereby matching the chemical composition of the tephra layers with their volcanic origin.
Far-traveled tephra from Mount St. Helens and Mazama have a silica content that typically ranges between 62 and 67 percent. Tephra from these two volcanoes appears white, gray, tan, or orange in color. Mount Rainier rocks and tephra contain 55 to 64 percent silica. Its tephra typically darker in color than tephra from Mount St. Helens and Mount Mazama.
*Make one copy of the following for each student: Student Page "Make Your Own Tephra Isopach Map", "Map of Cascade Volcanoes" and "Letter to the Geologists" assessment.
*Before class begins, determine whether you wish to project maps for all-class viewing or distribute a set of maps to each student or student group, and then make preparations. The maps that you must either make copies or project are "Exploring Tephra Layers at Mount Rainier (Tephra Maps 1-6)".
Print off for use during lesson.
Print off for use during lesson.
Either project for class viewing or copy one per student for investigation.
Make one copy per student.
Make one copy per student.
- Tell students that today they are going to solve a mystery. Geologists began studying tephra, or rock fragments ejected from a volcano, on the side of Mount Rainier. Mount Rainier is the highest mountain of the Cascade Range of the Pacific Northwest, and a volcano. However, they discovered a mystery: Some tephra layers on the flanks of Mount Rainier were not from the Mount Rainier volcano. The geologists wondered: How did tephra from other volcanoes in the Cascade Mountain Range end up on Mount Rainier?
- Explain to students that they will observe maps of tephra layers at Mount Rainier to solve this mystery.
- Think-Pair-Share: As students think on their own for one minute about what could be the answer to this mystery. Then, ask students to share their hypothesis with a partner. Lastly, make a list of class hypotheses on the board.
- Hand out the student page "Make Your Own Tephra Isopach Map" to each student.
- Ask students to write down the hypothesis they most agree with and read about the air flow around the Cascade volcanoes. They are instructed to draw a hypothetical tephra layer–a partly teardrop shape that delineates the outermost limit of a recognized tephra layer. This tephra layer originates at the summit crater and extends away from the volcano, as blown by prevailing winds. Be sure that students recognize this as a vertical view, with the observer looking down upon a tephra layer on the ground. This step should advance students' understanding of the general pattern of tephra fallout at volcanoes, and help them to interpret tephra maps 1 and 2.
- Instruct the students to draw circles (contours) to separate the zeros from the ones, the ones from the twos, the twos from the threes, and the threes from the fours (see example on teacher page, 10). These contours indicate areas of equal tephra thickness, known as isopachs. Explain that a tephra isopach map is a standard tool used by geologists who study volcanic eruptions.
2. Use overhead projection or handouts to project tephra maps 1 through 6 or provide paper copies to each student or student group. For each map, students should identify the wind direction at the time of the tephra eruption and a probable source volcano. Students should make note of the location of their community relative to the probable volcanic source and assess whether tephra from each eruption has fallen there. Use the "Map of Cascade Volcanoes" as a guide to this investigation.
3. Promote further discussion about what happens when the wind direction changes during the course of an eruption or when rising tephra reaches atmospheric levels where winds blow in opposing directions. Tephra fallout patterns can become complex, such as during the eruptions of Mount St. Helens in the 1980s, when complex atmospheric conditions resulted in complicated small-scale patterns of tephra fall across Washington State.
4. Return to the student page "Make Your Own Tephra Isopach Map". Instruct students to use a different color marker or pen to add to their student page maps, by drawing 3 to 5 hypothetical isopachs for a potential future tephra fall on Mount Rainier from a large eruption at Crater Lake. (Isopachs should appear as curved lines from the south, with decreasing thickness towards the north.) Provide additional scenarios for students' drawing of isopachs, such as the pattern of a tephra layer that results from easterly winds (which would result with a teardrop shape facing west).
5. Invite discussion about how this information can assist geologists who investigate a volcano's history and hazards. Explore the types of information that geologists can obtain from these maps, such as the volcanic source, area and volume of tephra erupted, and wind direction at the time of eruption.
6. Lead a discussion of energy transformation, where rising tephra gains potential energy as it rises and looses energy as it falls.
Optional: Provide students with information about some Pacific Northwest tephra layers by distributing the information on the teacher pages.
- Isopach - a line on a map or diagram connecting points beneath which a particular stratum or group of strata has the same thickness.
- Pumice - a very light and porous volcanic rock formed when a gas-rich froth of glassy lava solidifies rapidly.
- Scoria - a cindery, vesicular basaltic lava, typically having a frothy texture.
- Silica - a hard, unreactive, colorless compound that occurs as the mineral quartz and as a principal constituent of sandstone and other rocks.
- Tephra - rock fragments and particles ejected by a volcanic eruption.
- Volcanic Ash - very small solid particles ejected from a volcano during an eruption.
- Mount Rainier - Mount Rainier is the highest mountain of the Cascade Range of the Pacific Northwest, and the highest mountain in the state of Washington.
- Cascade Range - The Cascade Range or Cascades is a major mountain range of western North America, extending from Southern Canada through Washington and Oregon to Northern California.
Assessment MaterialsLetter to the Geologists
Students will write a letter to the Geologists of Mount Rainier with the answers to the mystery of the Tephra Layers.
Look for students' understanding of the following concepts:
*That wind disperses tephra.
*Tephra particle sizes are greatest near the volcano.
*Some tephra on the slopes of one volcano might have erupted from a different volcano.
*Students should understand that tephra layers provide a valuable record of previous eruptions.
Letter to the Geologists
Supports for Struggling Learners
*Provide students with information about some Pacific Northwest tephra layers by distributing the information on the teacher pages.
*Provide copies of maps to students.
*Use small blocks to build 3D version of tephra maps on the "Make Your Own Tephra Isopach Map" page. Put 2 small blocks on each number 2, 1 small block on each number 1, and no blocks where it says 0. This will help students visualize the 3D version of the volcano.
*Students research the tephra layers discussed in this activity. Students conduct a library or Internet search for information about the tephra layers discussed in this activity.
*Use kitchen ingredients to make a cross-sectional representation of tephra layers stacked one upon the other. Assemble cornmeal, cinnamon, oatmeal, flour, decorative sprinkles, and different colors of sugar, paper and glue sticks. Students draw a rectangle across one-half of a piece of construction paper. They take a pinch of each ingredient, and glue it on the paper from the bottom of the rectangle to the top. Each ingredient represents a layer of tephra. Students should label each layer, and then while observing the width of each layer on the paper and its relative particle size, add a few words about the eruptive event, such as "large eruption," "short eruption," "tephra from nearby eruption" and "tephra from far away."
*Use protractors with your study of tephra layers. Provide students with protractors and instruct them to determine precise compass directions of tephra fall for the "Tephra Maps," 1 through 6. For the student page "Make Your Own Tephra Isopach Map," choose some compass directions in degrees and instruct students to produce a tephra layer on the axis of the compass directions provided. Explore together what regions or communities would be affected by these hypothetical tephra eruptions
Mullineaux, D.R., 1974, Pumice and other pyroclastics in deposits at Mount Rainier National Park: U.S. Geological Survey Bulletin 1326, 83 p.
Crandell, D.R., 1969, Surficial geology of Mount Rainier National Park Washington: U.S. Geological Survey Bulletin 1288, 41 p.
Related Lessons or Education Materials
This lesson plan is part of the "Living with a Volcano in Your Backyard" curriculum, created through a partnership between Mount Rainier National Park and the US Geological Survey Cascades Volcano Observatory.