Till plains are an extensive flat

plain In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and ...

glacial till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

that forms when a sheet of

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

becomes detached from the main body of a

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

and melts in place, depositing the

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s 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 The Midwestern United States (also referred to as the Midwest, the Heartland or the American Midwest) is one of the four census regions defined by the United States Census Bureau. It occupies the northern central part of the United States. It ...

, due to multiple glaciation events that occurred in the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

epoch. During this period, the Laurentide Ice Sheet advanced and retreated during the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

epoch. Till plains formed by the

Wisconsin glaciation The Wisconsin glaciation, also called the Wisconsin glacial episode, was the most recent glacial period of the North American ice sheet complex, peaking more than 20,000 years ago. This advance included the Cordilleran Ice Sheet, which nucleated ...

cover much of the Midwest, including North Dakota, South Dakota, Indiana, Minnesota, Wisconsin, Iowa, Illinois, and northern

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

(see Glacial till plains (Ohio)). Ground moraine 9004

Characteristics

Till plains are large flat or gently sloping areas of land on which glacial

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

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. 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 Loam (in geology and soil science) is soil composed mostly of sand (particle size > ), silt (particle size > ), and a smaller amount of clay (particle size < ). By weight, its mineral composition is about 40–40–20% concentration of sand–si ...

texture due to variance in deposited material. Till plains are also the location in which drumlins, drumlin fields,

flutes The flute is a member of a family of musical instruments in the woodwind group. Like all woodwinds, flutes are aerophones, producing sound with a vibrating column of air. Flutes produce sound when the player's air flows across an opening. In th ...

, and additional moraines form, all composed of glacial till. 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.

Hydrogeologic importance

Subglacial meltwater is the main product of glacial

ablation Ablation ( – removal) is the removal or destruction of something from an object by vaporization, chipping, erosion, erosive processes, or by other means. Examples of ablative materials are described below, including spacecraft material for as ...

. 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.

Soil formation and fertility

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

deposits forming rich fertile soils, and the gently rolling to flat topography being very suitable for farming practices.

References

Glaciology Geomorphology {{Topography-stub

Characteristics

Hydrogeologic importance

Soil formation and fertility

See also

References