Lesson Plan

Tephra Explorer

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Grade Level:
Sixth Grade-Ninth Grade
Earth Science, Geography, Geology, Landscapes, Volcanoes
50 minutes or one class session
Group Size:
Up to 36
isopach, pumice, scoria, silica, tephra, volcanic ash, mount rainier, Mount Rainier National Park, Cascade Volcano Observatory, Cascade Range


Students view distribution patterns of tephra layers found around Mount Rainier and discover their source. 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.


Students will:
  • Understand general distribution patterns of tephra dispersal by wind at Mount Rainier.
  • Understand how to interpret an isopach map.
  • Recognize that some tephra at Mount Rainier originated at other Cascade volcanoes.



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.


Teacher and Student pages for the Tephra Explorer lesson plan; and supplemental graphics.



Look for students' understanding of the following concepts:

  1. That wind disperses tephra.
  2. Tephra particle sizes are greatest near the volcano.
  3. 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. Students might indicate that this knowledge helps scientists determine the kinds of eruptions that happen at a given volcano, and ultimately the most likely eruption types for the future. Understanding what types of eruptions that can happen in the future ultimately saves lives and property and improves the well being of nearby communities.

Park Connections

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. This activity demonstrates how wind has the ability to carry volcanic ash from surrounding eruptions.


  • 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."  

Additional Resources

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.


Last updated: February 28, 2015