Tephrachronology
Dating by Volcanic Ash
Volcanoes in the Pacific Northwest are known for their ash clouds
which can deposit a thin layer of ash in their wake for hundreds
of miles. Scientists frequently use these ash, or tephra layers,
to date artifacts and archaeological sites found in the soil.
Move your mouse over the image at right to determine the age of
various tephra layers.
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Test yourself: If an artifact is found below an ash layer
that was deposited 2,600 years ago, then what is the youngest age
of that artifact?
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Another test: If an artifact is found just above a layer
that is 8,600 years old what is the youngest age of that artifact?
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