In geology, drift is a name for all

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

(

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...

boulder In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In c ...

s) transported by a

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...

and deposited directly by or from the ice, or by

glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

meltwater Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater can be ...

. Drift is often subdivided into (unsorted and) unstratified drift (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

moraine A moraine is any accumulation of unconsolidated debris (regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice shee ...

s and stratified drift (glaciolacustrine and fluvioglacial sediments) that accumulates as stratified and sorted sediments in the form of

outwash plain An outwash plain, also called a sandur (plural: ''sandurs''), sandr or sandar, is a plain formed of glaciofluvial deposits due to meltwater outwash at the terminus of a glacier. As it flows, the glacier grinds the underlying rock surface and c ...

esker An esker, eskar, eschar, or os, sometimes called an ''asar'', ''osar'', or ''serpent kame'', is a long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North Amer ...

kame A kame, or ''knob'', is a glacial landform, an irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier, and is then deposited on the land surface with further melting of the g ...

varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (va ...

s, and so forth. The term drift clay is a synonym for

boulder clay Boulder clay is an unsorted agglomeration of clastic sediment that is unstratified and structureless and contains gravel of various sizes, shapes, and compositions distributed at random in a fine-grained matrix. The fine-grained matrix consists o ...

. Both are archaic terms for glacial tills with a fine-grained matrix.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2005. ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. In the United Kingdom, drift is also applied as a general term for all surficial, unconsolidated, rock debris and sediment that is moved from one place to accumulate in another and mapped separately or otherwise diffrerentiated from underlying

bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...

. In this usage, ''drift'' includes a wide variety of deposits, e.g.

loess Loess (, ; from german: Löss ) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits. Loess is a periglacial or aeolian ...

, glacial till, river deposits,

colluvium Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combinatio ...

, and so forth, of

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

age. However, this term is most commonly used to specifically describe glacial deposits.Allaby, M., 2013. ''A Dictionary of Geology and Earth Science''. Oxford, United Kingdom, Oxford University Press. 720 pp.

Etymology

In 1839, geologist Roderick MurchisonMurchison, R.I., 1839. ''The Silurian System, Founded on Geological Researches in the Counties of Salop, Hereford, Radnor, Montgomery, Caermarthen, Brecon, Pembroke, Monmouth, Gloucester, Worcester, and Stafford: With Descriptions of the Coalfields and Overlying Formations.'' London, United Kingdom, John Murray, vol. 1, 768 pp. introduced the term ''drift'' to describe unconsolidated surficial sediments previously called ''

diluvium Diluvium is an archaic term applied during the 1800s to widespread surficial deposits of sediments that could not be explained by the historic action of rivers and seas. Diluvium was initially argued to have been deposited by the action of extra ...

''. The term ''drift'' refers to the drift hypothesis proposed by

Charles Lyell Sir Charles Lyell, 1st Baronet, (14 November 1797 – 22 February 1875) was a Scottish geologist who demonstrated the power of known natural causes in explaining the earth's history. He is best known as the author of ''Principles of Geolo ...

,Lyell, C., 1833. ''Principles of Geology''. London, United Kingdom, John Murray, vol. 3, 398 pp. as influenced by contemporary polar research, that these sediments had been transported by sea ice and icebergs drifting in marine currents. The drift hypothesis further proposed that these sediments had been released as the ice melted, to fall and accumulate on the sea floor in comparatively recent times, e.g. during the Quaternary Period. This term continued to be used long after the drift hypothesis had been abandoned in favor of the glacial theory.Harland, W.B., Herod, K.N. and Krinsley, D.H., 1966. ''The definition and identification of tills and tillites''. ''Earth-Science Reviews'', 2, pp.225-256.

References

External links

* Glacial deposits {{Glaciology-stub

Etymology

See also

References

External links