Varve formation during the past three centuries in three large proglacial lakes in south-central Alaska
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.
Citation Information
Publication Year | 2018 |
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Title | Varve formation during the past three centuries in three large proglacial lakes in south-central Alaska |
DOI | 10.1130/B31792.1 |
Authors | Evelin Boes, Maarten Van Daele, Jasper Moernaut, Sabine Schmidt, Britta J.L. Jensen, Nore Praet, Darrell Kaufman, Peter J. Haeussler, Michael G. Loso, Marc De Batist |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Geological Society of America Bulletin |
Index ID | 70217648 |
Record Source | USGS Publications Warehouse |
USGS Organization | Alaska Science Center Geology Minerals |