Red Rock Canyon — Tuff

Tuff is an igneous rock that forms from the compaction of volcanic ash. The soft, porous rock may range in age from Precambrian to recent. The chemical composition and thickness may vary within an area with extensive deposits. The only requirement for tuff is that the materials are air fall from the eruption of a volcano.

Tuff is classified on the basis of what it contains and the size of the embedded particles. Tuff can contain dust-size to boulder-size particles, and many have small crystalline fragments which have formed by the compression of sediment. Since different volcanoes have different types of magma, tuff may form from magma with rhyolite, andesitic, basaltic, and other types of magma.

Often, the particles that are ejected are soft and sticky and upon landing on earth they "weld" together. This type of rock often has large chunks of material interspersed with smaller particles. Welded tuff may be found near the vent of the volcano.

This rock has been used in construction for walls, especially in the Mediterranean where tuff is abundant. Throughout history, it has been used in sculpture. Due to its porous nature, it may not be capable of supporting a great deal of weight. Care must be taken when building a structure on a tuff field since it may collapse during an earthquake.

Discussion Questions:

  • Why is there different colored tuff?
  • How does tuff differ from pumice?
  • Why is some of the red tuff layer on top of the white while some of the red tuff is below the white layer?

"What Is Tuff?"


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