What is Tuff?

Mary McMahon
Mary McMahon

Tuff is a type of rock which is formed from compacted volcanic ash and fragments of material associated with volcanic eruptions. There are a number of different types, with the rock being classified on the basis of what it contains, how large the particles embedded in the rock are, and how it formed. Tuff has limited commercial uses, although it was once used extensively in building and sculpture in some regions because it was so readily available.

Tuff is compacted ash and material from volcanic eruptions.
Tuff is compacted ash and material from volcanic eruptions.

When volcanoes erupt, they spew massive amounts of ash, fragments of rock, and other materials into the air. As these materials settle and cool, they form into an assortment of rock varieties, including tuff. This rock commonly forms when volcanic magma is very stiff, allowing air bubbles and pockets to form, and it tends to be extremely porous and very soft; depending on the prevailing conditions, it may have several layers of material, reflecting multiple eruptions.

In some cases, tuff actually welds together, because the components of the rock are so hot. In this case, it is classified as a pyroclastic rock, and it is called “welded tuff.” This type of rock is often very easy to identify, because it typically has large chunks of material interspersed with smaller ones, all welded together by the heat of the ash and other components.

Tuff may also be classified on the basis of the composition of its fragments. Basaltic, ultramafic, rhyolite, and andesitic tuff are some examples of various types. Many of these forms have small crystalline fragments, which can sometimes cause the rock to sparkle or glitter. They are classified as sedimentary rocks, because they are formed by the deposition and compression of sediment.

In construction, this rock can be useful, especially for things like walls, and numerous examples of tuff walls can be seen in places like the Mediterranean, where it is abundant. Tuff has also historically been used in sculpture. In areas where it is common, people have to be careful when they are building homes and other structures, as tuff is not always capable of supporting a great deal of weight. A house built over a tuff field may collapse during an earthquake, and cuttings in railway embankments and along roads are also subject to crumbling and damage.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


How long does it take for tuff to form?


@anon138117 - In addition to the tuff found in Rome and San Salvador, welded tuffs cover large areas in Peru, New Zealand, Yellowstone National Park, and Guatemala.


@anon138117 - Rome and San Salvador both have tuff. Builders in Rome have used tuff to construct buildings, both in ancient times and modern times. This tuff needs to be compacted carefully before construction, or washouts and landslides can wipe the buildings away from their foundations. This occurred in San Salvador during the earthquake of 2001, when multiple buildings constructed upon tuff collapsed.


You are a great help but i would put where in the earth it is located.

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