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The impact and significance of tephra deposition on a Holocene forest environment in the North Cascades, Washington, USA

Egan, Joanne; Fletcher, William J.; Allott, Tim E. H.; Lane, Christine S.; Blackford, Jeff J.; Clark, Douglas H.


Joanne Egan

William J. Fletcher

Tim E. H. Allott

Christine S. Lane

Jeff J. Blackford

Douglas H. Clark


© 2016 Elsevier Ltd. High-resolution palaeoecological analyses (stratigraphy, tephra geochemistry, radiocarbon dating, pollen and ordination) were used to reconstruct a Holocene vegetation history of a watershed in the Pacific Northwest of America to evaluate the effects and duration of tephra deposition on a forest environment and the significance of these effects compared to long-term trends. Three tephra deposits were detected and evaluated: MLF-T158 and MLC-T324 from the climactic eruption of Mount Mazama, MLC-T480 from a Late Pleistocene eruption of Mount Mazama and MLC-T485 from a Glacier Peak eruption. Records were examined from both the centre and fringe of the basin to elucidate regional and local effects. The significance of tephra impacts independent of underlying long-term trends was confirmed using partial redundancy analysis. Tephra deposition from the climactic eruption of Mount Mazama approximately 7600 cal. years BP caused a significant local impact, reflected in the fringe location by changes to open habitat vegetation (Cyperaceae and Poaceae) and changes in aquatic macrophytes (Myriophyllum spicatum, Potamogeton, Equisetum and the alga Pediastrum). There was no significant impact of the climactic Mazama tephra or other tephras detected on the pollen record of the central core. Changes in this core are potentially climate driven. Overall, significant tephra fall was demonstrated through high resolution analyses indicating a local effect on the terrestrial and aquatic environment, but there was no significant impact on the regional forest dependent of underlying environmental changes.


Egan, J., Fletcher, W. J., Allott, T. E. H., Lane, C. S., Blackford, J. J., & Clark, D. H. (2016). The impact and significance of tephra deposition on a Holocene forest environment in the North Cascades, Washington, USA. Quaternary science reviews, 137(April), 135-155.

Journal Article Type Article
Acceptance Date Feb 11, 2016
Online Publication Date Feb 23, 2016
Publication Date Apr 1, 2016
Deposit Date Apr 5, 2016
Publicly Available Date Apr 5, 2016
Journal Quaternary science reviews
Print ISSN 0277-3791
Electronic ISSN 1873-457X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 137
Issue April
Pages 135-155
Keywords Tephra impact; Holocene environmental change; Pollen; Mazama; Glacier peak; Redundancy analysis
Public URL
Publisher URL
Additional Information Authors' accepted manuscript of article published in: Quaternary science reviews, 2016, v.137.


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