GLACIAL LAKE MISSOULA OUTBURST FLOODS AND THE SOUTHWESTERN CORDILLERAN 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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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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Geomorphology, hydrology, and chronology of Early Holocene jökulhlaups along the Hvítá River and Gullfoss waterfall, Iceland

10.5194/egusphere-egu21-15752 ◽

2021 ◽

Author(s):

Greta Wells ◽

Sheryl Luzzadder-Beach ◽

Timothy Beach ◽

Thorsteinn Saemundsson ◽

Andrew Dugmore

Keyword(s):

Source Region ◽

Ice Sheet ◽

Flood Frequency ◽

Early Holocene ◽

Glacial Lake ◽

Quarter Century ◽

Alpine Regions ◽

Outburst Floods ◽

Geothermal Activity ◽

Glacial Outburst Floods

Glacial outburst floods (j&#246;kulhlaups) have occurred across Earth throughout the Quaternary, often leaving a geomorphologic, sedimentological, and climatic legacy that extends far beyond the source region and can persist for millennia. Furthermore, they pose an increasing geohazard in glaciated landscapes worldwide due to climate-driven ice retreat. Iceland experiences more frequent j&#246;kulhlaups than nearly anywhere on Earth, though most research focuses on floods triggered by subglacial volcanic and geothermal activity. However, abundant evidence also exists for non-volcanogenic floods from proglacial lakes, which may serve as a better analogue for most global j&#246;kulhlaups.As the Icelandic Ice Sheet retreated across Iceland in the Late Pleistocene-Early Holocene, meltwater lakes formed 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 canyon systems, scoured bedrock, boulder deposits, and Gullfoss&#8212;Iceland&#8217;s most famous waterfall. The largest events reached an estimated peak discharge on the order of 105 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 from a quarter-century ago.This project employs a combination of field, modelling, and laboratory methods to better constrain flood timing and dynamics at this underexplored site. This talk synthesizes geomorphologic field mapping, HEC-RAS hydraulic simulations and paleohydraulic calculations, and cosmogenic nuclide exposure dates to reconstruct Kj&#246;lur j&#246;kulhlaup routing, hydrology, and chronology. It situates these events within the context of Pleistocene-Holocene Icelandic Ice Sheet retreat and paleoenvironmental change, presenting a series of scenarios of ice margin position, glacial lake extent, and j&#246;kulhlaup drainage. Finally, it assesses the Kj&#246;lur j&#246;kulhlaups as an analogue to contemporary glacial outburst floods in other Arctic and alpine regions in terms of flood frequency, dynamics, and landscape impact.

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The pattern and style of deglaciation at the Late Wisconsinan Laurentide and Cordilleran ice sheet limits in northeastern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2016-0066 ◽

2017 ◽

Vol 54 (1) ◽

pp. 52-75 ◽

Cited By ~ 4

Author(s):

David H. Huntley ◽

Adrian S. Hickin ◽

Olav B. Lian

Keyword(s):

British Columbia ◽

Ice Sheets ◽

Ice Sheet ◽

Yukon Territory ◽

Glacial Lake ◽

Glacial Lakes ◽

Lake Formation ◽

Late Wisconsinan ◽

Cordilleran Ice Sheet ◽

Lake Deposits

This paper reports on the landform assemblages at the northern confluence of the Late Wisconsinan Laurentide and Cordilleran ice sheets with montane and piedmont glaciers in the northern Rockies and southern Mackenzie Mountains. Recent observations in northeastern British Columbia refine our knowledge of the pattern and style of ice sheet retreat, glacial lake formation, and meltwater drainage. At the onset of deglaciation, confluent Laurentide and Cordilleran terminal ice margins lay between 59°N, 124°30′W and 60°N, 125°15′W. From this terminal limit, ice sheets retreated into north-central British Columbia and Yukon Territory, with remnant Cordilleran ice and montane glaciers confined to mountain valleys and the Liard Plateau. Distinctive end moraines are not associated with the retreat of Cordilleran ice in these areas. Laurentide ice retreated northeastward from uplands and the plateaus; then separated into lobes occupying the Fort Nelson and Petitot river valleys. Ice-retreat landforms include recessional end moraines (sometimes overridden and drumlinized), hill–hole pairs, crevasse-fill deposits, De Geer-like ribbed till ridges, hummocky moraines, kames, meltwater features, and glacial lake deposits that fall within the elevation range of glacial Lake Liard and glacial Lake Fort Nelson (ca. 840–380 m). Meltwater and sediment transport into glacial lakes Fort Nelson, Liard, Nahanni, and Mackenzie was sustained by remnant ice in the Liard River and Fort Nelson River drainage basins until the end of glaciation. Optical dating of sand from stabilized parabolic dunes on the Liard Plateau indicates that proglacial conditions, lake formation, and drainage began before 13.0 ± 0.5 ka (calendar years). The Petitot, Fort Nelson, and Liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes Peace and Hay.

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