Varve formation during the past three centuries in three large proglacial lakes in south-central Alaska

Geological Society of America Bulletin
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Abstract

The sediments stored in the large, deep proglacial lakes of south-central Alaska are largely unstudied. We analyzed sediments in 20 cores, up to 160 cm long, from Eklutna, Kenai, and Skilak Lakes, using a combination of repeated lamination counting, radionuclide dating, event stratigraphy, and tephrochronology. We show that the characteristically rhythmic layers were deposited annually. Most of these glacial varves consist of one coarse-grained base and a fine-grained top, but varves composed of multiple coarse-grained turbidite pulses are common too. They are likely related to successive episodes of high sediment discharge during flooding, and they become more frequent in all three lakes, along with increased sedimentation rates, during the nineteenth century late phase of the Little Ice Age. These flood turbidites were generated by rain events and intense melting of snow and ice. Other (mega) turbidites are a result of earthquake-triggered slope collapses (e.g., A.D. 1964). Some event layers are present in all three lakes. In addition, the annual time series of varve thickness (normalized annual sedimentation rate) are significantly correlated among the three lakes (ρ > 0.27; p < 0.001). Differences between the varve thickness records can be attributed partly to the dam construction at Eklutna Lake and outbursts from an ice-dammed lake at Skilak Lake. Geomorphologic differences among the catchments result in further differences in sedimentation patterns in the three lakes.

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Publication type Article
Publication Subtype Journal Article
Title Varve formation during the past three centuries in three large proglacial lakes in south-central Alaska
Series title Geological Society of America Bulletin
DOI 10.1130/B31792.1
Volume 130
Issue 5-6
Year Published 2018
Language English
Publisher Geological Society of America
Contributing office(s) Alaska Science Center Geology Minerals
Description 18 p.
First page 757
Last page 774
Country United States
State Alaska
Other Geospatial Kenai Mountains
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