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? Background 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 o Duration: 60 Minutes.