DESCRIPTION:
Formed from the glacial melt-waters 13,000 years ago, Lake Agassiz
covered much of Manitoba, including St. Norbert. Partial drainage of
the lake 10,000 years ago saw the shoreline recede north of the
junction of the Red and Assiniboine Rivers, making this region
inhabitable to the Amerindians.
Recent studies link sea level rise from the Lake Agassiz drainage of
8,500 years ago to the expansion of agriculture from East to West
across Europe and further suggest the rise may also account for
various flood myths of prehistoric cultures, including the Biblical flood
narrative. Link: Lake Agassiz Animation
Lake Agassiz
Lake Agassiz was an immense glacial lake located in the middle of the
northern part of North America. Fed by glacial melt water at the end of
the last glacial period, its area was larger than all of the modern Great
Lakes combined though its mean depth was not as great as that of
many major lakes today.
First postulated in 1823 by William H. Keating, it was named by
Warren Upham in 1879 after Louis Agassiz, when Upham recognized
that the lake was formed by glacial action.
Geological progression
During the last Ice Age, northern North America was covered by a
glacier, which alternately advanced and deteriorated with variations in
the climate. This continental ice sheet formed during the period now
known as the Wisconsin glaciation, and covered much of central North
America between 30,000 and 10,000 years ago. As the ice sheet
disintegrated, it created at its front an immense proglacial lake,
formed from its melt waters, as the retreat of glacial margins is not
caused by a reversal of the glacier's flow, but rather from melting of
the ice sheet.
Around 13,000 years ago, the lake came to cover much of Manitoba,
northwestern Ontario, northern Minnesota, eastern North Dakota, and
Saskatchewan. At its greatest extent, it may have covered as much as
440,000 km2 (170,000 sq mi), larger than any currently existing lake
in the world (including the Caspian Sea) and approximately the size of
the Black Sea.
The lake drained at various times south through the Traverse Gap into
Glacial River Warren (parent to the Minnesota River, a tributary of the
Mississippi River), east through Lake Kelvin (modern Lake Nipigon) to
what is now Lake Superior, or west via the Mackenzie River through
the Northwest Territories.
Geologists have found evidence that a major outbreak of Lake Agassiz,
about 13,000 years ago, drained north through the Mackenzie River
into the Arctic Ocean. A return of the ice for some time offered a
reprieve, but after retreating north of the Canada–United States
border around 10,000 years ago, Lake Agassiz refilled.
The last major shift in drainage occurred around 8,200 years ago. The
melting of remaining Hudson Bay ice caused Lake Agassiz to drain
nearly completely. This final drainage of Lake Agassiz is associated
with an estimated 0.8 to 2.8 m (2.6 to 9.2 ft) rise in global sea levels.
Glacial Lake Agassiz and Lake Ojibway (7,900 YBP) Lake Agassiz'
major drainage reorganization events were of such magnitudes that
they had significant impact on climate, sea level and possibly early
human civilization.
Major freshwater release into the Arctic Ocean is considered to disrupt
oceanic circulation and cause temporary cooling. The draining of
13,000 years ago may be the cause of the Younger Dryas stadial.
The draining at 9,900–10,000 years ago may be the cause of the
8,200 yr climate event. A recent study by Turney and Brown links the
8,500 years ago drainage to the expansion of agriculture from east to
west across Europe; he suggests that this may also account for various
flood myths of prehistoric cultures, including the Biblical flood
narrative.
Glacial River Warren outlet
The lowest point between the drainage of Hudson Bay and the Gulf of
Mexico is in the Traverse Gap between the U.S. states of Minnesota
and South Dakota. It lies between Lake Traverse and Big Stone Lake.
This sub-continental divide is about 300 meters (980 ft) above sea
level. When Lake Agassiz existed the gap was the outlet of River
Warren.
The outflow from the melting glaciers filled Lake Agassiz and then
drained through the gap to the Gulf of Mexico. This mass of moving
water eroded a valley about 2–5 kilometers (1.2–3.1 mi) wide and
from 100 feet (30 m) to 125 feet (38 m) deep.
Today, this valley contains the Minnesota River, joined by the Upper
Mississippi River at Mendota, Minnesota. The northern part of the
former lakebed is the valley of the Red River of the North, which flows
northward to Lake Winnipeg.[14]
Lockhart Phase of Lake Agassiz: 12,875–12,560 YBP
During the Lockhart
Phase, water
accumulated in the Red
River valley of North
Dakota and Minnesota.
As the water reached to
the top of the divide to
the south, the water
drained into the
ancestral Minnesota and
Mississippi River system.
This occurred while the
Laurentian Ice Sheet was
at or below the current
U.S. and Canadian
border.
As the ice sheet melted northward, an early Lake Agassiz covered
southern Manitoba, the Minnesota and Ontario boundary country, and
along the Red River south of Fargo, North Dakota. The Lockhart phase
is associated with the Herman lake stage (335 metres (1,099 ft)), the
highest shoreline of Lake Agassiz. The Big Stone Moraine formed the
southern boundary of the lake. During the Lockhart Phase the lake is
estimated to have been 231 metres (758 ft) deep, with greater depths
near the glacier.
The Moorhead Phase: 12,560–11,690 YBP
As the ice sheet melted northward, Lake Agassiz found a lower outlet
through the Kaministikwia route along the modern Minnesota–Ontario
border. This moved water to Lake Duluth a pro-glacial lake in the Lake
Superior basin. From there the water drained south via an ancestral
St. Croix and Mississippi River system. The lake drained below the
Herman lake beaches until isostatic rebound and glacial advances
closed the Kaministikwia route. This stabilized the lake at the Norcross
lake stage (325 metres (1,066 ft)).
The average depth of Lake Agassiz during the late Moorhead Phase
was 258 metres (846 ft). Drainage from Lake Agassiz continued to
flow southward out of the ancient Minnesota and Mississippi River
systems into the Gulf of Mexico.
Emerson Phase: 11,690–10,630 YBP
During the Emerson Phase lake levels and drainage patterns
continually fluctuated. The lake moved from a southward outlet to a
northwestern outlet, and may have been static without a significant
outlet during this phase. Isostatic rebound changed the altitude of the
land, and this, combined with changes in the volume of melt-water
from the ice margin and the closure of the Kaministikwia outlet in the
east increased the size of the northern end of the lake.
One hypothesis postulates that the lake was a ‘terminal lake’ with
water inflows and evapotranspiration being equal. Dating of the glacial
moraines shows that the Clearwater and Athabasca River system and
Lake Nipigon and Minong basin were still ice covered. A period of
precipitation and meltwater input balance with the rate of evapotranspiration may have existed for a short period of time. During this
phase, the Clearwater and Athabasca River system outlet opened.
Isostatic rebound opened the southern outlet for a time, creating the
Norcross (325 metres (1,066 ft)), Tintah (310 metres (1,020 ft))), and
Upper Campbell (299 metres (981 ft)) beaches. The south outlet was
permanently closed at the end of Emerson Phase.
Nipigon Phase: 10,630–9,160 YBP
The opening of the Kaministikwia outlet to the east initiated the onset
of the Nipigon Phase. The lower lake level ended the southern outlet
through the ancestral Minnesota and Mississippi River system. The ice
sheets advance and blocked the northwestern outlet through the
Clearwater and Athabasca system. There were several other low level
outlets into the Lake Minong basin, including the Kaministikwia and the
Lake Nipigon outlet. These allowed large amounts of water to flow
from Lake Agassiz into Lake Minong.
A series of ice advances and retreats between 10,500 and to 9,500
YBP blocked the Lake Nipigon outlet and the other low level outlets,
creating periodic catastrophic outbursts of water into the Lake Minong
basin. These large inflows of water raised Lake Minong lake levels and
flowed into Lake Algonquin in the Lake Michigan/Huron basin. These
outbursts refilled the Lake Michigan and Huron basins, which are
extreme low water levels of the Lake Chippewa (Lake Michigan basin)
and Lake Stanley (Lake Huron basin). This was due to isostatic
rebound of the northern shorelines combined with the opening of the
North Bay outlet of the Lake Huron basin.
These repetitive outbursts from Lake Agassiz flooded the Lake Minong
basin, then flowed over into the Lake Stanley basin, and then flowed
through the North Bay drainage route into the Champlain Sea (present
day St. Lawrence lowland).
The shifting ice sheet created fluctuating drainage channels into the
Lake Nipigon and Superior basin. A dozen beaches were created during
short periods of stability. Towards the end of the Nipising Phase, Lake
Agassiz reached its largest geographical size as it joined with Lake
Ojibway in the east.
Ojibway Phase: 9,160–8,480 YBP
Map of Glacial Lake Agassiz and Lake Ojibway ca 7900 YBP
The Ojibway Phase is named for the glacial lake along the ice front in
northern Ontario. Lake Ojibway merged with Lake Agassiz at this time.
Isostatic rebound glaciated lands south of the ice sheet created a long
linear lake from the Saskatchewan–Manitoba border to Quebec. This
long lake drained through the eastern outlet at Kinojevis, into the
Ottawa River valley.
Lake Agassiz-Ojibway drainage raised the sea level. The results can be
seen in Nova Scotia, New Brunswick, and eastern Maine. Marine
records from the North Atlantic have identified two separate episodes,
linked to northern hemisphere cooling in 8,490 YBP and 8,180–8,340
YBP. These may be linked with the Ojibway Phase of Lake Agassiz and
may indicate large amounts of drainage from the Ottawa River valley
and the Tyrrell Sea (ancestral Hudson Bay).
The Laurentide Ice Sheet continued to recede. Continued warming
shrank the ice front towards present day Hudson Bay. Here, the Lake
Agassiz northward outlet drained into the Tyrrell Sea. This breach
dropped the water level below the eastern Kinojevis outlet. The
drainage was followed by the disintegration of the adjacent ice front at
about 8,480 YBP. This brought on the end of Lake Agassiz. The ice
sheet continued its northward retreat to Baffin Island, leaving the
mainland North America around 5,000 YBP
Remnants and effects
Lake Winnipeg, Lake Winnipegosis, Lake Manitoba, Red Lake, and Lake
of the Woods, among others, are relicts of the ancient lake. Other
geological and geomorphological evidence for Lake Agassiz can also be
seen today. Raised beaches, many kilometers from any water, mark
the former boundaries of the lake at various times.
While the Red River gradually descends from south to north, these old
strandlines ascend as one goes north, due to isostatic rebound since
glaciation. Several modern river valleys, including those of the
Assiniboine River and the Minnesota River, were originally cut by water
entering or leaving the lake. The fertile soils of the Red River Valley,
now drained by the Red River of the North, are formed from lacustrine
deposits of silt from Lake Agassiz.
http://en.wikipedia.org/wiki/Lake_Agassiz
Lake Agassiz outburst sparked 'Big Freeze' in Europe
12,800 years ago
Lake Agassiz outburst
sparked 'Big Freeze'
in Europe 12,800
years ago. When an
ice wall collapsed
somewhere along
Lake Agassiz's
northeastern rim
about 12,800 years
ago, its freshwater
contents gushed
rapidly into the North Atlantic, wreaking havoc with ocean circulation
patterns and plunging Europe into an unprecedented and prolonged
winter that lasted centuries. In a study that highlights just how quickly
a mini ice age took hold of Europe after the dramatic collapse of a
glacial ice dam in ancient Canada, Saskatoon scientist Bill Patterson
has gathered evidence suggesting the "Big Freeze" - a sudden and
severe global cooling known to experts as the Younger Dryas happened within three months of the Canadian cataclysm. But rather
than unfolding over a decade as widely believed, the extreme chill set
in so swiftly that ecosystems in the northern hemisphere were
radically transformed within a single season, a research project led by
Patterson has discovered. "If (Canada's earliest aboriginals) lived near
Agassiz, they may simply have seen the lake level drop as the lake
shrunk in size," Patterson said. "If they were in the East near the
outlet, they would have seen what would look like a large, fast flowing
river."
http://www.geostrategis.com/p_agassiz.htm
Louis Agassiz
(Lake Agassiz Namesake)
Louis Agassiz,
May 28, 1807 – December 14, 1873,
was a Swiss-born and European-trained biologist
and geologist recognized as an innovative and
prodigious scholar of Earth's natural history, with
later American writings that have received
scrutiny because of particular racial themes.
Agassiz grew up in Switzerland, and studied and
received Doctor of Philosophy and medical
degrees at Erlangen and Munich, respectively.
After further studies with Cuvier and von
Humboldt in Paris, Agassiz proceeded with
research leading to his appointment as professor of natural history at
University of Neuchâtel.
After visiting Harvard University mid-career, he emigrated to the U.S.
in 1847 and became a professor of zoology and geology at Harvard,
and to head its Lawrence Scientific School and found its Museum of
Comparative Zoology. Agassiz made extensive contributions to
ichthyological classification (including of extinct species) and to the
study of geological history (including to the founding of glaciology),
and has become broadly known through student descriptions a
thorough regimen of observational data gathering and analysis. The
impressiveness of his vast institutional and scientific contributions to
zoology, geology, and related areas—including many multivolume
research series running to thousands of pages—has been somewhat
tarnished by the evidence of his resistance to theories of Darwinian
evolution, and his extensive later writings on polygenism.
http://en.wikipedia.org/wiki/Louis_Agassiz