Reply to comments by on: “Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonia Ice Sheet”

Newly examined exposures in northern Idaho and Washington show that catastrophic floods from glacial Lake Missoula during late Wisconsin time were repeated, brief jökulhlaups separated by decades of quiet glaciolacustrine and subaerial conditions. Glacial Priest Lake, dammed in the Priest River valley by a tongue of the Purcell trench lobe of the Cordilleran ice sheet, generally accumulated varved mud; the varved mud is sharply interrupted by 14 sand beds deposited by upvalley-running currents. The sand beds are texturally and structurally similar to slackwater sediment in valleys in southern Washington that were backflooded by outbursts from glacial Lake Missoula. Beds of varved mud also accumulated in glacial Lake Spokane (or Columbia?) in Latah Creek valley and elsewhere in northeastern Washington; the mud beds were disrupted, in places violently, during emplacement of each of 16 or more thick flood-gravel beds. This history corroborates evidence from southern Washington that only one graded bed is deposited per flood, refuting a conventional idea that many beds accumulated per flood. The total number of such floodlaid beds in stratigraphic succession near Spokane is at least 28. The mud beds between most of the floodlaid beds in these valleys each consist of between 20 and 55 silt-to-clay varves. Lacustrine environments in northern Idaho and Washington therefore persisted for two to six decades between regularly recurring, colossal floods from glacial Lake Missoula.

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Antarctic Supraglacial Lake Identification Using Landsat-8 Image Classification

Remote Sensing ◽

10.3390/rs12081327 ◽

2020 ◽

Vol 12 (8) ◽

pp. 1327 ◽

Cited By ~ 1

Author(s):

Anna Ruth W. Halberstadt ◽

Colin J. Gleason ◽

Mahsa S. Moussavi ◽

Allen Pope ◽

Luke D. Trusel ◽

...

Keyword(s):

Large Scale ◽

Seasonal Pattern ◽

Ice Sheet ◽

Training Data ◽

Landsat 8 ◽

Ice Shelf ◽

Ice Shelves ◽

Continental Scale ◽

Lake Evolution ◽

Supervised Classifiers

Surface meltwater generated on ice shelves fringing the Antarctic Ice Sheet can drive ice-shelf collapse, leading to ice sheet mass loss and contributing to global sea level rise. A quantitative assessment of supraglacial lake evolution is required to understand the influence of Antarctic surface meltwater on ice-sheet and ice-shelf stability. Cloud computing platforms have made the required remote sensing analysis computationally trivial, yet a careful evaluation of image processing techniques for pan-Antarctic lake mapping has yet to be performed. This work paves the way for automating lake identification at a continental scale throughout the satellite observational record via a thorough methodological analysis. We deploy a suite of different trained supervised classifiers to map and quantify supraglacial lake areas from multispectral Landsat-8 scenes, using training data generated via manual interpretation of the results from k-means clustering. Best results are obtained using training datasets that comprise spectrally diverse unsupervised clusters from multiple regions and that include rock and cloud shadow classes. We successfully apply our trained supervised classifiers across two ice shelves with different supraglacial lake characteristics above a threshold sun elevation of 20°, achieving classification accuracies of over 90% when compared to manually generated validation datasets. The application of our trained classifiers produces a seasonal pattern of lake evolution. Cloud shadowed areas hinder large-scale application of our classifiers, as in previous work. Our results show that caution is required before deploying ‘off the shelf’ algorithms for lake mapping in Antarctica, and suggest that careful scrutiny of training data and desired output classes is essential for accurate results. Our supervised classification technique provides an alternative and independent method of lake identification to inform the development of a continent-wide supraglacial lake mapping product.

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Catastrophic glacial-lake outburst flooding of the Patagonian Ice Sheet

Earth-Science Reviews ◽

10.1016/j.earscirev.2019.102996 ◽

2020 ◽

Vol 200 ◽

pp. 102996 ◽

Cited By ~ 13

Author(s):

Gerardo Benito ◽

Varyl R. Thorndycraft

Keyword(s):

Ice Sheet ◽

Glacial Lake

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Mechanism of Till Deposition Related to Thermal Conditions in a Pleistocene Glacier

Journal of Glaciology ◽

10.3189/s0022143000022061 ◽

1971 ◽

Vol 10 (60) ◽

pp. 363-373

Author(s):

John Shaw

Keyword(s):

Environmental Conditions ◽

Lacustrine Sediments ◽

Ice Sheet ◽

Thermal Conditions ◽

Basal Part ◽

Glacial Lake ◽

Depositional Processes ◽

Polar Type ◽

Lake Deposits ◽

The Relationship

AbstractA record of sedimentation from pro-glacial sandur deposits through pro-glacial lake deposits to final deposition of till is used to interpret changing environmental conditions, and depositional processes, during the development of the “Little Welsh Advance” in the Shrewsbury area, England. The relationship between lacustrine sediments and till establishes till deposition by flowage. However, the most important conclusions are derived from the deduction that lacustrine sediments were incorporated into the basal part of the ice sheet and transported across previously deposited end moraines. A discussion of this deduction, based on the findings of Weertman (1961), establishes that during the advancing phase the ice sheet was of the polar type. Final melting is thought to have occurred by both top-melt and under-melt as a result of climatic amelioration.

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Reconstruction of Early Holocene jokulhlaups along the Hvita River and Gullfoss waterfall, Iceland

10.5194/egusphere-egu2020-1065 ◽

2020 ◽

Author(s):

Greta Wells ◽

Þorsteinn Sæmundsson ◽

Sheryl Luzzadder-Beach ◽

Timothy Beach ◽

Andrew Dugmore

Keyword(s):

Ice Sheet ◽

Hydraulic Modeling ◽

Early Holocene ◽

Glacial Lake ◽

Exposure Dating ◽

Alpine Regions ◽

Outburst Floods ◽

Lake Formation ◽

Geothermal Activity ◽

Downstream Communities

Glacial lake outburst floods (GLOFs) have occurred across the planet throughout the Quaternary and are a significant geohazard in Arctic and alpine regions today. Iceland experiences more frequent GLOFs&#8212;known in Icelandic as j&#246;kulhlaups&#8212;than nearly anywhere on Earth, yet most research focuses on floods triggered by subglacial volcanic and geothermal activity. However, floods from proglacial lakes may be a better analogue to most global GLOFs.As the Icelandic Ice Sheet retreated across Iceland in the Late Pleistocene-Early Holocene, meltwater pooled at ice margins and periodically drained in j&#246;kulhlaups. Some of the most catastrophic floods drained from ice-dammed Glacial Lake Kj&#246;lur, surging across southwestern Iceland from the interior highlands to the Atlantic Ocean. These floods left extensive geomorphologic evidence along the modern-day course of the Hv&#237;t&#225; River, including canyons, scoured bedrock, boulder deposits, and Gullfoss&#8212;Iceland&#8217;s most famous waterfall. The largest events reached an estimated maximum peak discharge of 300,000 m3 s-1, ranking them among the largest known floods in Iceland and on Earth.Yet, all our evidence for the Kj&#246;lur j&#246;kulhlaups comes from only one publication to date (T&#243;masson, 1993). My research employs new methods to better constrain flood timing, routing, magnitude, and recurrence interval at this underexplored site. This talk presents new and synthesized j&#246;kulhlaup geomorphologic evidence; HEC-RAS hydraulic modeling results of flow magnitude and routing; and ongoing geochronological analyses using cosmogenic nuclide exposure dating and tephrochronology. It also situates these events within Icelandic Ice Sheet deglaciation chronology and environmental change at the Pleistocene-Holocene transition. Finally, it examines the Kj&#246;lur floods as an analogue to contemporary ice sheet response, proglacial lake formation, and j&#246;kulhlaup processes and landscape evolution in Arctic and alpine regions worldwide, where GLOFs pose an increasing risk to downstream communities due to climate-driven meltwater lake expansion. &#160;Citation: T&#243;masson, H., 1993. J&#246;kulst&#237;flu&#240; v&#246;tn &#225; Kili og hamfarahlaup &#237; Hv&#237;t&#225; &#237; &#193;rness&#253;slu. N&#225;tt&#250;rufr&#230;&#240;ingurinn 62, 77-98.

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Sedimentology, stratigraphy, and geomorphology of glacial Lake Calgary at Cochrane, Alberta, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e99-010 ◽

1999 ◽

Vol 36 (5) ◽

pp. 791-803 ◽

Cited By ~ 7

Author(s):

Timothy G Fisher

Keyword(s):

Field Data ◽

Ice Sheet ◽

Laurentide Ice Sheet ◽

Glacial Lake ◽

Fluvial Sediment

Stratigraphic and sedimentologic field data in the Cochrane, Alberta, area demonstrate that glaciolacustrine sediment comprising the Calgary Formation underlies glaciofluvial and fluvial sediment of the Bighill Creek Formation, previously dated at 11.4 ka BP. A continuous, conformable contact between sediments of glacial Lake Calgary and underlying till indicates that the lake was coeval with initial deglaciation of the area. The lake formed during retreat of the Cordilleran ice up the Bow Valley that was once previously coalescent with the Laurentide Ice Sheet. Rhythmic, graded, and convoluted glaciolacustrine sediments record continuous and high rates of sedimentation in this reach of glacial Lake Calgary, further implying that the lake formed early in deglacial time.

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