Fort Towson

The Yn tephra is a geologically recent tephra deposit that covers portions of the U.S. state of Washington and the Canadian provinces of British Columbia and Alberta. It was created by the largest known volcanic eruption from Mount St. Helens, having taken place in possibly 1860 BCE as part of the Smith Creek eruptive period. The tephra consists of pumiceous dacite.^[2]

References

^ ^a ^b "St. Helens". Global Volcanism Program. Smithsonian Institution. Retrieved 2020-01-28.
^ Pallister, John S.; Clynne, Michael A.; Wright, Heather M.; Van Eaton, Alexa R.; Vallance, James W.; Sherrod, David R.; Kokelaar, B. Peter (2017). "Eruptive History". Field-Trip Guide to Mount St. Helens, Washington—An Overview of the Eruptive History and Petrology, Tephra Deposits, 1980 Pyroclastic Density Current Deposits, and the Crater. United States Department of the Interior. p. 11. ISSN 2328-0328.

[SI-1] "St. Helens". Global Volcanism Program. Smithsonian Institution. Retrieved 2020-01-28.

[2] Pallister, John S.; Clynne, Michael A.; Wright, Heather M.; Van Eaton, Alexa R.; Vallance, James W.; Sherrod, David R.; Kokelaar, B. Peter (2017). "Eruptive History". Field-Trip Guide to Mount St. Helens, Washington—An Overview of the Eruptive History and Petrology, Tephra Deposits, 1980 Pyroclastic Density Current Deposits, and the Crater. United States Department of the Interior. p. 11. ISSN 2328-0328.

[2]