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Lake Agassiz
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It was the biggest climate event of the last 10,000 years and caused the most dramatic change in the weather since humans began farming. And it may yet hold important lessons about climate change in the 21st century.
Just over 8000 years ago, a huge glacial lake in Canada burst, and an estimated 100,000 cubic kilometres of fresh water rushed into the North Atlantic. Researchers now say they know for sure that this catastrophic event shut down the Gulf Stream and cooled parts of the northern hemisphere by several degrees for more than a hundred years.
They say the findings show modelling studies are right to suggest that something similar could happen with equal abruptness as the planet warms under human influence. The film The Day After Tomorrow, which portrays such a scenario, may have exaggerated but not by much.
Lake Agassiz was a giant lake that formed at the end of the last ice age as the huge Laurentide ice sheet melted (see a simulation of the process). The lake occupied most of the modern-day Canadian Midwest between the Hudson Bay and the US border.

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RE: Hudson Flood
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For those unfamiliar with east coast United States geography, New York City is at the far western end of Long Island, where the Hudson River empties into the Atlantic Ocean.
The first general aspect to point out is how broad this shelf is compared to the west coast of the US. At this location, the shelf is 180 km  wide; along much of California it is on the order of 15 km  wide, more-or-less. This is a function of a passive continental margin vs. an active margin. Along the east coast, the continental to oceanic crust transition is an old rifted margin. The active spreading centre (the Mid-Atlantic Ridge) is now 2,800 km  away. In this area, the rifting of continents started in the Triassic (225 million years ago). In other words, this margin has been relatively quiet (tectonically) since then, hence the passive adjective.

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Hudson Shelf Valley
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 The 150-km-long Hudson Shelf Valley, the largest physiographic feature on the mid-Atlantic continental shelf, bisects the New York Bight region. The Valley is the submerged seaward extension of the ancestral Hudson River drainage system that, unlike other valleys on the Atlantic shelf, has not been filled with sediment. A survey of the topography and backscatter intensity of the valley has been carried out using a Simrad Subsea EM 1000 multibeam sea floor mapping system. The valley head is located in a broad shallow basin and extends offshore 5-40 m below the shelf surface to a seaward terminus at a shelf-edge delta. The valley can be divided into upper, middle, lower and outer sections based on the topography, surficial sediments, and drainage pattern. The middle valley is characterized by 5 local topographic lows along the valley axis that have relief of 3-11 m below the valley floor. The northwestern portion of the study area has been affected by disposal of dredged and other materials since the late 1800's. Part of this area has been designated as the Historic Area Remediation Site (HARS). The sea floor of the HARS is being remediated by placing at least a one-meter cap of clean dredged material on top of the existing surface sediments that exhibit varying degrees of degradation. A large field of sand waves is located in the lower valley in 70-80 m water depth that cover an area approximately 30 km long and 4 km wide. This sand wave field is hypothesized to be part of a flood deposit that formed as a result of the break-out of glacial lakes in upstate New York approximately 13,500 years BP. In the eastern-most part of the survey area in water depths greater than about 110 m, the sea floor is marked by long narrow northeast-southwest-trending grooves that are interpreted to be iceberg scour marks.

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L

Posts: 131433
Date:
Lake Agassiz
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Scientists seeking the cause of a big freeze that hit shortly after the last ice age have eliminated one prime suspect: a gigantic lake spilling into the Atlantic Ocean and disrupting warm water currents. Experts say the new research provides valuable lessons for scientists attempting to predict the consequences of today's warming trend.
About 8200 years ago, the paleoclimate record suggests, temperatures across the Northern Hemisphere plummeted. Within a century or so, that half of the globe appeared ready to plunge into another ice age, although temperatures eventually warmed again. For years, scientists have been trying to figure out what caused the cooling. One popular possibility has been the draining of Lake Agassiz. The lake, which spread over much of central Canada and the northern United States and at its maximum covered more area than all of the Great Lakes combined, emerged as the glaciers melted. Eventually, Lake Agassiz's water poured out through Hudson Bay and into the northwestern Atlantic Ocean off the coast of Labrador. Researchers suspected that by dumping a huge amount of fresh cold water into the ocean within a few hundred years, the lake might have disrupted the currents that transport warm water from the tropics to eastern North America, Greenland, and Western Europe.

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L

Posts: 131433
Date:
Hudson Flood
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Wednesday morning, May 23, reporters are invited to see the debut of a new map that depicts how our local geology was significantly altered 10,000 to 15,000 years ago by the great ice age floods that raced through central Washington. This large colourful map (18"x32"), which will be made available free to the public features two self-guided road tours that identify many geologic highlights such as 'The Badlands' of Benton City, gigantic erratics (boulders) that hitchhiked on ancient icebergs, and the Chandler Butte landslide. Brief narratives identify the significance of Wallula Gap, the impacts the historic floods made to local soils and how that benefited our agriculture and wine industry, a list of two dozen wineries in the vicinity, plus many full colour photos and useful graphics.

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L

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Date:
Ice Age Floods
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Pacific Northwest National Laboratory geologists have put out a call for teeth tusks, femurs and any and all other parts of extinct mammoths left by massive Ice Age floods in southeastern Washington.
The fossils, in some cases whole skeletons of Mammathus columbi, the Columbian mammoth, were deposited in the hillsides of what are now the Yakima, Columbia and Walla Walla valleys in southeastern Washington, where the elephantine corpses came to rest as water receded from the temporary but repeatedly formed ancient Lake Lewis. PNNL geologists are plotting the deposits to reconstruct the high-water marks of many of the floods, the last of which occurred as recently as 12,000 to 15,000 years ago.

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This Saturday, March 31, volunteers will gather to put the final touches on a new interpretive kiosk being constructed at Richland's new Trailhead Park at the base of Badger Mountain.
The kiosk is one of several interpretive projects being developed to highlight the area's geologic history; providing awareness and understanding of the Ice Age Floods that ravaged the Northwest thousands of years ago.
While this kiosk is a Team Battelle community project, volunteers from several organizations have been active partners, contributing to its design and construction. A Team Battelle representative will be available to explain the purpose and significance of this community effort. The president of the Ice Age Floods Institute also will be present to provide a progress report on the bills before Congress that target support for the proposed Ice Age Floods National Geologic Trail (the kiosk is an element of this effort).

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RE: Hudson Canyon
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hudsoncanyon

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RE: Hudson Flood
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Title: Sea Floor Topography and Backscatter Intensity of the Hudson Canyon Region Offshore of New York and New Jersey
Author: Bradford Butman, David C. Twichell, Peter A. Rona, Brian E. Tucholke, Tammie J. Middleton, and James M. Robb.

This report presents maps of the sea floor topography and backscatter intensity of the Hudson Canyon region on the continental slope and rise offshore of New Jersey and New York at a scale of 1:300,000. Sheet 1 shows sea floor topography as shaded relief. Sheet 2 shows sea floor topography as shaded relief with backscatter intensity superimposed in colour. Sheet 1 also contains interpretive text, and both sheets contain figures and tables that further present and describe the data. The maps are based on multibeam echo-sounder data collected on an 18-day cruise carried out aboard the National Oceanic and Atmospheric Administration (NOAA) Ship Ronald H. Brown during August and September 2002.

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Posts: 131433
Date:
Lake Iroquois
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Ocean circulation changes during the present warm interglacial were more extensive than previously thought, according to new research by the University of East Anglia (UEA) and Cardiff University.

The findings, reported in this week's edition of the international journal Science (30 June 2006), prove for the first time that sudden North American 'lake bursts' slowed ocean circulation and cooled the climate approximately 8200 years ago. The groundbreaking research increases our understanding of the complex link between ocean circulation and climate change and highlights the sensitivity of the Atlantic overturning circulation to freshwater forcing.
Christopher Ellison and Dr Mark Chapman, of UEA's School of Environmental Sciences, and Dr Ian Hall, of Cardiff University's School of Earth, Ocean and Planetary Sciences, investigated whether there was a connection between the catastrophic freshwater release from glacial lakes in North America, ocean circulation changes and the dramatic cooling seen in many climate records approximately 8200 years ago. The research team studied a sediment core taken from the seabed of the North Atlantic.

"The core contains sediments representing the warm interval since the last Ice Age. The sediment includes a variety of small animals called foraminifera that record surface water conditions in their shells when living. We analysed changes in the abundance of different species of foraminifera and the chemistry of the shells to examine past patterns of climate change. We also analysed the sediment grain size to gauge the speed of deep ocean currents and therefore the strength of ocean circulation." - Christopher Ellison, University of East Anglia.

The new findings provide direct evidence of both the freshwater forcing and the climate response.

"The 8200-year-old event is the most recent abrupt climate change event and by far the most extreme cooling episode in the last 10,000 years, but up until now we knew comparatively little about its impact, if any, on the ocean circulation. Our records show a sequenced pattern of freshening and cooling of the North Atlantic sea surface and an associated change in the deep ocean circulation, all key factors that are involved in controlling the state of northern hemisphere climate." - Dr Mark Chapman, University of East Anglia.

"The impact of large-scale pulsed inputs of freshwater on ocean circulation and climate during the time of the last Ice Age are well documented, but our results clearly demonstrate that these sorts of abrupt reorganisations also can occur during periods of warm climate. These findings have important implications for future research because they aid our understanding of the magnitude of forcing involved in rapid climate changes and the mechanisms involved. This provides a useful target for assessing the models that are used to predict future patterns of climate change" - Dr Ian Hall, Cardiff University.

The study was supported by the Natural Environment Research Council and is part of a national programme, RAPID, aimed at improving scientist's ability to quantify the probability and magnitude of future rapid change in climate.

Source University of East Anglia

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