Wisconsinan glaciation
Encyclopedia
The Wisconsin Glacial Episode was the most recent major advance
of the North American Laurentide
ice sheet. Globally, this advance is known as the last glacial period. The Wisconsin glaciation extended from approximately 110,000 to 10,000 years ago, between the Eemian interglacial
and the current interglacial. The maximum ice extent occurred approximately 21,000 years ago during the last glacial maximum
, also known as the Late Wisconsin in North America.
The Wisconsin glaciation radically altered the geography of North America north of the Ohio River
. At the height of the Wisconsin Episode glaciation, the ice sheet
covered most of Canada
, the Upper Midwest
, and New England
, as well as parts of Idaho
, Montana
and Washington. On Kelleys Island in Lake Erie
or in New York
's Central Park
the grooves left by these glaciers can be easily observed. In southwestern Saskatchewan
and southeastern Alberta
, a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, the northernmost point in North America that remained south of the continental ice sheets. At the height of glaciation the Bering land bridge
potentially permitted migration of mammals, including humans, to North America from Siberia
.
across the Bering Strait
allowed the first humans to reach North America from Asia (an alternative theory is migration along the coast; see Settlement of the Americas). Human migration routes opened during interglacial periods in Europe and Asia as well.
-core samples in present day northern Arizona. Here in the Waterman Hills
researchers found that Juniperus osteosperma
and Pinus monophylla were early to mid-Holocene dominant trees, while Monardella arizonica
has been a continuously present understory plant. Celtis reticulata
is an example of a plant present in the early Holocene following Wisconsin glacial retreat, which species is no longer present at the Waterman Mountains
site.
Glacial period
A glacial period is an interval of time within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate within an ice age...
of the North American Laurentide
Laurentide ice sheet
The Laurentide Ice Sheet was a massive sheet of ice that covered hundreds of thousands of square miles, including most of Canada and a large portion of the northern United States, multiple times during Quaternary glacial epochs. It last covered most of northern North America between c. 95,000 and...
ice sheet. Globally, this advance is known as the last glacial period. The Wisconsin glaciation extended from approximately 110,000 to 10,000 years ago, between the Eemian interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
and the current interglacial. The maximum ice extent occurred approximately 21,000 years ago during the last glacial maximum
Last Glacial Maximum
The Last Glacial Maximum refers to a period in the Earth's climate history when ice sheets were at their maximum extension, between 26,500 and 19,000–20,000 years ago, marking the peak of the last glacial period. During this time, vast ice sheets covered much of North America, northern Europe and...
, also known as the Late Wisconsin in North America.
The Wisconsin glaciation radically altered the geography of North America north of the Ohio River
Ohio River
The Ohio River is the largest tributary, by volume, of the Mississippi River. At the confluence, the Ohio is even bigger than the Mississippi and, thus, is hydrologically the main stream of the whole river system, including the Allegheny River further upstream...
. At the height of the Wisconsin Episode glaciation, the ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
covered most of Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, the Upper Midwest
Upper Midwest
The Upper Midwest is a region in the northern portion of the U.S. Census Bureau's Midwestern United States. It is largely a sub-region of the midwest. Although there are no uniformly agreed-upon boundaries, the region is most commonly used to refer to the states of Minnesota, Wisconsin, and...
, and New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
, as well as parts of Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
, Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
and Washington. On Kelleys Island in Lake Erie
Lake Erie
Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...
or in New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
's Central Park
Central Park
Central Park is a public park in the center of Manhattan in New York City, United States. The park initially opened in 1857, on of city-owned land. In 1858, Frederick Law Olmsted and Calvert Vaux won a design competition to improve and expand the park with a plan they entitled the Greensward Plan...
the grooves left by these glaciers can be easily observed. In southwestern Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
and southeastern Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
, a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, the northernmost point in North America that remained south of the continental ice sheets. At the height of glaciation the Bering land bridge
Bering land bridge
The Bering land bridge was a land bridge roughly 1,000 miles wide at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages. Like most of Siberia and all of Manchuria, Beringia was not glaciated because snowfall was extremely light...
potentially permitted migration of mammals, including humans, to North America from Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
.
Role in human migration
Prehistoric human migration was greatly influenced by the Last glacial period, known in North America as the Wisconsin glaciation. In the late Wisconsin era, a land bridgeLand bridge
A land bridge, in biogeography, is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonise new lands...
across the Bering Strait
Bering Strait
The Bering Strait , known to natives as Imakpik, is a sea strait between Cape Dezhnev, Chukotka Autonomous Okrug, Russia, the easternmost point of the Asian continent and Cape Prince of Wales, Alaska, USA, the westernmost point of the North American continent, with latitude of about 65°40'N,...
allowed the first humans to reach North America from Asia (an alternative theory is migration along the coast; see Settlement of the Americas). Human migration routes opened during interglacial periods in Europe and Asia as well.
Flora and fauna
North American flora and fauna species were distributed quite differently during the Wisconsin era, due to altered temperatures, surface water distribution and, in some cases, coverage of earth surface by glaciers. A number of scientific studies have been conducted to determine species distribution, particularly during the Late Wisconsin and early to mid-Holocene. An example of findings is from the investigation of flora species using pollenPollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
-core samples in present day northern Arizona. Here in the Waterman Hills
Waterman Hills
The Waterman Hills are a low mountain range in the Mojave Desert, just north of Barstow in San Bernardino County, California....
researchers found that Juniperus osteosperma
Juniperus osteosperma
Juniperus osteosperma is a shrub or small tree reaching 3-6 m tall. It is native to the southwestern United States, in Utah, Nevada, Arizona, western New Mexico, western Colorado, Wyoming, southern Montana, southern Idaho and eastern California...
and Pinus monophylla were early to mid-Holocene dominant trees, while Monardella arizonica
Monardella arizonica
Monardella arizonica is a plant species endemic to Arizona in the USA. Plants within the genus are commonly known as wildmint, coyote mint or monardella.-Ancient history:...
has been a continuously present understory plant. Celtis reticulata
Celtis reticulata
Celtis reticulata, with common names including Netleaf Hackberry, Western Hackberry, Douglas Hackberry, Netleaf Sugar Hackberry, Palo Blanco, Acibuche, is a small to medium size deciduous tree, native to western North America.-Prehistoric:Celtis reticulata was one of the species analyzed in a...
is an example of a plant present in the early Holocene following Wisconsin glacial retreat, which species is no longer present at the Waterman Mountains
Waterman Mountains
The Waterman Mountains are a low mountainous landform in Pima County, United States. Numerous flora and fauna species are found in the Waterman Mountains, in the Pinyon-juniper woodland plant community. Notable among the tree species is the Elephant tree which species exhibits a contorted...
site.
In the Sierra Nevada
In the Sierra Nevada, there are three named stages of glacial maxima (sometimes incorrectly called ice ages) separated by warmer periods. These glacial maxima are called, from oldest to youngest, Tahoe, Tenaya, and Tioga. The Tahoe reached its maximum extent perhaps about 70,000 years ago. Little is known about the Tenaya. The Tioga was the least severe and last of the Wisconsin Episode.See also
- Glacial history of MinnesotaGlacial history of MinnesotaThe glacial history of Minnesota is most defined since the onset of the last glacial period, which ended some 10,000 years ago. Within the last million years, most of the Midwestern United States and much of Canada were covered at one time or another with an ice sheet. This continental glacier had...
- Last glacial period
- Younger DryasYounger DryasThe Younger Dryas stadial, also referred to as the Big Freeze, was a geologically brief period of cold climatic conditions and drought between approximately 12.8 and 11.5 ka BP, or 12,800 and 11,500 years before present...
- Timeline of glaciationTimeline of glaciationThere have been five known ice ages in the Earth's history, with the Earth experiencing the Quaternary Ice Age during the present time. Within ice ages, there exist periods of more severe glacial conditions and more temperate referred to as glacial periods and interglacial periods, respectively...
- Ice coreIce coreAn ice core is a core sample that is typically removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice...