What is tuff rock formed from volcanic ash?

Tuff is a type of rock created when volcanic ash is ejected from a vent during an eruption and later lithifies into solid rock. Rock that is made of more than 75% ash is classified specifically as tuff. Because it is relatively soft, tuff has historically been used for construction and carving, including by the Romans and the Rapa Nui people for moai statues.

What we know

• Tuff is a rock type formed from volcanic ash ejected during eruptions that subsequently lithifies into solid rock. [3]
• Rock containing greater than 75% volcanic ash is categorized as tuff. [3]
• Despite being classified in igneous petrology, tuff can sometimes be described using sedimentological terms and is soft enough for ancient construction. [3]
• The Lava Creek Tuff is a voluminous ash-flow sheet covering over 7,500 square kilometers, created during Yellowstone's third volcanic cycle around 640,000 years ago. [2]

Where to go next

• what caused itHow did the Yellowstone Caldera form?
• a case in pointWhat are moai statues made of?
• how it workedHow does loose volcanic ash become solid rock?
• compared withWhat is the difference between tuff and tufa?
• the bigger pictureWhat are pyroclastic rocks?
• an unexpected connectionHow were the Easter Island statues carved from volcanic remnants?Volcanic ash formations like tuff are soft enough to be carved into massive monumental statues such as the moai on Easter Island.

Sources

• [1]Lava Creek Tuff (Wikidata Q3219737) · CC0 1.0
• [2]Lava Creek Tuff · CC BY-SA 4.0
• [3]Tuff · CC BY-SA 4.0
• [4]Kneeling Nun Tuff · CC BY-SA 4.0
• [5]Fort Rock · CC BY-SA 4.0