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Geosciences: Forged in flames, but not always fireproof

Munich, 05/08/2012

Volcanic tuff has long been a popular building material, and is found not only in the many buildings in Rome, Naples and environs, but also in Cologne Cathedral. LMU researchers have now shown that, although formed in volcanic eruptions, some tuffs actually become unstable at high temperatures.

Tuffs are born in explosive volcanic eruptions, when large amounts of ash and fragments of molten rock are blown high into the air. As they cool, these components solidify to form a type of rock that is soft and is easy to work with, and has been used extensively in building construction for centuries. However, despite their fiery origins, some types of tuff react to heat in adverse ways, as volcanologists at LMU have recently shown.  Specifically, it turns out that zeolite-containing tuffs effectively represent a fire hazard. This is because zeolites, which are silicate minerals, lose water and become unstable when exposed to high temperatures.

Structures with a built-in plasticizer
Such instability can have a drastic effect on the strength of a tuff. In large-scale fires, temperatures can routinely reach values of around 1000°C. At such temperatures, zeolite-containing tuffs may lose up to 80% of their strength, enough to compromise the structural stability of entire buildings. Given that tuffs are frequently used for the construction of buildings in tectonically active regions, where earthquakes and volcanic eruptions are often accompanied by catastrophic fires, the new finding has obvious implications for tuff-based structures - and their inhabitants - in these areas. The authors of the new study therefore recommend that zeolite levels should be routinely determined before tuffs are approved for construction purposes. Given its potential repercussions, it is not surprising that the new work has occasioned much comment in scientific journals, including Nature. (Geology, April 2012)

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