Plain of glacial till
Till plains
are an extensive flat
plain
of
glacial till
that forms when a sheet of
ice
becomes detached from the main body of a
glacier
and melts in place, depositing the
sediments
it carried.
Ground moraines
are formed with melts out of the glacier in irregular heaps, forming rolling hills. Till plains are common in areas such as the Midwestern United States, due to multiple glaciation events that occurred in the
Holocene
epoch. During this period, the
Laurentide Ice Sheet
advanced and retreated during the
Pleistocene
epoch.
[1]
Till plains formed by the
Wisconsin glaciation
cover much of the Midwest, including North Dakota, South Dakota, Indiana, Minnesota, Wisconsin, Iowa, Illinois, and northern
Ohio
(see
Glacial till plains (Ohio)
).
[2]
Characteristics
[
edit
]
Till plains are large flat or gently sloping areas of land on which glacial
till
has been deposited from a melted glacier. In some areas, these depositions can be up to hundreds of feet thick. The morphology of the till plain is generally reflective of the topography of the bedrock below the glacier. Another term for till plain is
ground moraine
. Not to be confused with
outwash plains
, till plains differ due to their sorting mechanisms and resulting deposit characteristics.
[3]
Till plains are deposited as unsorted material picked up by ice as glaciers advance and retreat, or if a body of ice becomes detached from the main glacier and melts in place. Glacial till contain various sizes of material from clay to large glacial erratics, and form a
loam
texture due to variance in deposited material. Till plains are also the location in which
drumlins
, drumlin fields,
flutes
, and additional
moraines
form, all composed of glacial till.
[4]
The material composition of till plains vary greatly, and is dependent on the travel path of the transporting glacier, indicated by the provenance of the deposited material. Till plains may be deposited as a single sheet of till, but often a single plain may contain multiple sheets of till. This occurs where changing climate and/or ice dynamics led to multiple phases of glacier advance and retreat.
[5]
Hydrogeologic importance
[
edit
]
Subglacial meltwater is the main product of glacial
ablation
. This meltwater acts as the force that causes subglacial tills to deform, and also plays a significant role in shaping the morphology and distribution of the till on the till plain. The composition of till plains is economically important due to their hydraulic properties. This property typically makes them confining units, or
aquitards
, which inhibit groundwater flow. Meltwater, as well as groundwater, tends to preferentially flow through subglacial sediment deposits, given that they are sufficiently porous, soft, and deformable. The flow regime is assumed to be either
darcian
or
advective
flows, although the precise method is often speculated and debated.
[6]
Soil formation and fertility
[
edit
]
During the last glaciation, much of the Midwestern and Central United States were covered by glaciers. As the glaciers retreated and melted, much of the land was covered in till plains. These till plains were the basis from which the present day soil formed from. The parent material which these soils formed from varies greatly from one area to another, and is dependent on the path of the glacier which deposited the initial glacial till. This has caused different soils to form over time, but most generally share similar properties such as a
loamy
texture and poor drainage if derived from glacial till. The soils developed from till plains have become some of the most productive agricultural regions in the United States, due to the combination of thick
till
deposits forming rich fertile soils, and the gently rolling to flat topography being very suitable for farming practices.
[6]
See also
[
edit
]
References
[
edit
]
- ^
"The Importance of Glaciers to Wisconsin"
.
Schlitz Audubon
. 2019-01-15
. Retrieved
2020-11-26
.
- ^
"The retreat chronology of the Laurentide Ice Sheet during the last 10,000 years and implications for deglacial sea-level rise"
.
Vignette Collection
. Retrieved
2020-12-18
.
- ^
Janowski, Lukasz; Tylmann, Karol; Trzcinska, Karolina; Rudowski, Stanislaw; Tegowski, Jaroslaw (2021).
"Exploration of Glacial Landforms by Object-Based Image Analysis and Spectral Parameters of Digital Elevation Model"
.
IEEE Transactions on Geoscience and Remote Sensing
.
60
: 1?17.
doi
:
10.1109/TGRS.2021.3091771
.
- ^
"Geotechnical Engineering Manual - MnDOT"
.
www.dot.state.mn.us
. Retrieved
2020-11-25
.
- ^
Lusardi, Barbara A.; Jennings, Carrie E.; Harris, Kenneth L. (2011). "Provenance of des Moines lobe till records ice-stream catchment evolution during Laurentide deglaciation".
Boreas
.
40
(4): 585?597.
Bibcode
:
2011Borea..40..585L
.
doi
:
10.1111/j.1502-3885.2011.00208.x
.
S2CID
129303587
.
- ^
a
b
Bennett, Matthew (2009).
Glacial Geology: Ice Sheets and Landforms
. Wiley-Blackwell. pp. 81?107.
ISBN
978-0-470-51690-4
.
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Types
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Anatomy
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Processes
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Measurements
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Volcanic relations
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Landforms
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Continental glaciations
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General
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Landforms
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North America
| Canada
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United
States
|
- Chippewa Moraine State Recreation Area
, Wisconsin
- Coteau des Prairies
, South Dakota
- Devil's Lake State Park
, Wisconsin
- Glacial Lake Wisconsin
, Wisconsin
- Glacial Lakes State Park
, Minnesota
- Horicon Marsh State Wildlife Area
, Wisconsin
- Ice Age Floods National Geologic Trail
, Idaho, Oregon and Washington
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, Wisconsin
- Ice Age Trail
, Wisconsin
- Interstate State Park
, Minnesota and Wisconsin
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, Ohio
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, Wisconsin
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, Utah
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, Nevada
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, Montana
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, Wisconsin
- Oneida Lake
, New York
- Two Creeks Buried Forest State Natural Area
, Wisconsin
- Withrow Moraine and Jameson Lake Drumlin Field
, Washington
- Yosemite National Park
, California
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