When did the first volcano erupt?

rocky Kerry Jay

Dear Kerry,

The oldest volcano is billions of years old. Old rocks, a billion years or more, tend to be beat up a bit (or more). They might be folded and faulted. The might have their original minerals replaced by a new set of minerals. The original volcanic edifice (stratovolcano, shield, etc.) probably won't be recognizable. None of these would stop a volcanologist from getting all the information she could out of the rock. An age can be determined and the chemistry can tell a lot. Sometimes pillow lava or ropy pahoehoe lava can be found.

Volcanologists have found old volcanic rocks in the cratons of most continents. Here's a brief list of places and ages:

Canada: 3.5 to 2.8 billion years

Rhodesia (Zimbabwe): 3.4 billion years

South Africa: 3.3 billion years

West Australia: 2.8 billion years

West Australia: 3.1 billion years

3.5 billion years seems to be the oldest age for a volcano. Since the oldest known rocks are 3.96 billion years old, you might ask why there are not any volcanic rocks older than 3.5 billion years. There might be and they have not been found (funding mapping projects is not very popular these days). More likely they did exist and were changed by high pressure and temperature into metamorphic rock. If I spent a day in the library I could probably find the age of the oldest metamorphic rock that used to be volcanic. But I'm happy with 3.5 billion years. Hope you are too.

Thanks for a good question.

Steve Mattox, University of North Dakota

Sources of Information:
Palfreyman, W.D., 1984, Guide to the geology of Australia: Bureau of Mineral Resources, Geology, and Geophysics Bulletin 181, 111 p.

Wilson, H.D.B., and Morrice, M.G., The volcanic sequence in Archean shields: The Geological Society of Canada Special Paper Number 16, p. 355-374. 

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