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A moraine is any accumulation of unconsolidated debris (
regolith
Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestr ...
and
rock
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wales ...
), 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 sheet. It may consist of partly rounded particles ranging in size from boulders (in which case it is often referred to as boulder clay) down to gravel and sand, in a groundmass of finely-divided clayey material sometimes called
glacial flour
Rock flour, or glacial flour, consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion or by artificial grinding to a similar size. Because the material is very small, it becomes suspe ...
. Lateral moraines are those formed at the side of the ice flow, and
terminal moraine
A terminal moraine, also called end moraine, is a type of moraine that forms at the terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed by the front edge ...
s were formed at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines (
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 ...
-covered areas forming sheets on flat or irregular
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
) and medial moraines (moraines formed where two glaciers meet).
Etymology
The word ''moraine'' is borrowed from French , which in turn is derived from the Savoyard Italian ("mound of earth"). ''Morena'' in this case was derived from Provençal ''morre'' ("snout"), itself from Vulgar Latin ''*murrum'' "rounded object". The term was introduced into geology by
Horace Bénédict de Saussure
Horace Bénédict de Saussure (17 February 1740 – 22 January 1799) was a Genevan geologist, meteorologist, physicist, mountaineer and Alpine explorer, often called the founder of alpinism and modern meteorology, and considered to be the firs ...
in 1779.
Characteristics
Moraines are
landforms
A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, m ...
composed of
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 ...
deposited primarily by glacial ice.
[ Glacial till, in turn, is unstratified and unsorted debris ranging in size from ]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 ...
-sized glacial flour
Rock flour, or glacial flour, consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion or by artificial grinding to a similar size. Because the material is very small, it becomes suspe ...
to large boulders. The individual rock fragments are typically sub-angular to rounded in shape. Moraines may be found on the glacier's surface or deposited as piles or sheets of debris where the glacier has melted.
Formation
Moraines may form through a number of processes, depending on the characteristics of sediment, the dynamics on the ice, and the location on the glacier in which the moraine is formed. Moraine forming processes may be loosely divided into ''passive'' and ''active''.
''Passive'' processes involve the placing of chaotic supraglacial sediments onto the landscape with limited reworking, typically forming hummock
In geology, a hummock is a small knoll or mound above ground.Bates, Robert L. and Julia A. Jackson, ed. (1984). “hummock.” Dictionary of Geological Terms, 3rd Ed. New York: Anchor Books. p. 241. They are typically less than in height and ...
y moraines. These moraines are composed of supraglacial sediments from the ice surface.
''Active'' processes form or rework moraine sediment directly by the movement of ice, known as glaciotectonism. These form push moraines and thrust-block moraines, which are often composed of 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 ...
and reworked proglacial sediment.
Moraine may also form by the accumulation of sand and gravel deposits from glacial streams emanating from the ice margin. These fan deposits may coalesce to form a long moraine bank marking the ice margin. Several processes may combine to form and rework a single moraine, and most moraines record a continuum of processes. Reworking of moraines may lead to the formation of placer deposit
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. The name is from the Spanish word ''placer'', meaning "alluvial sand". Placer min ...
s of gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
as is the case of southernmost Chile.
File:Ansel Adams - National Archives 79-AA-M02.jpg, Moraine in Rocky Mountain National Park
Rocky Mountain National Park is an American national park located approximately northwest of Denver in north-central Colorado, within the Front Range of the Rocky Mountains. The park is situated between the towns of Estes Park to the east and ...
, taken by Ansel Adams
Ansel Easton Adams (February 20, 1902 – April 22, 1984) was an American landscape photographer and environmentalist known for his black-and-white images of the American West. He helped found Group f/64, an association of photographers advoca ...
in 1941.
File:Icy-lake.jpg, Moraines around the Icy lake (2709 m), just below Musala
Musala ( bg, Мусала ); from Arabic language, Arabic through Ottoman Turkish language, Ottoman Turkish: from ''Musalla'', "near God" or "place for prayer" is the highest mountain, peak in the Rila, Rila Mountains, as well as in Bulgaria and ...
peak (2925 m) in Rila Mountain
Rila ( bg, Рила, ) is the highest mountain range of Bulgaria, the Balkan Peninsula and Southeast Europe. It is situated in southwestern Bulgaria and forms part of the Rila– Rhodope Massif. The highest summit is Musala at an elevation of 2,92 ...
, Bulgaria
Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedon ...
.
File:Moraines Surlej.jpg, Lateral moraines of a retreating 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 ...
in Engadin
The Engadin or Engadine ( rm, ;This is the name in the two Romansh idioms that are spoken in the Engadin, Vallader and Puter, as well as in Sursilvan and Rumantsch Grischun. In Surmiran, the name is ''Nagiadegna'', and in Sutsilvan, it is ' ...
.
File:Colline moreniche del Lago Garda.JPG, Moraine of Lake Garda
Lake Garda ( it, Lago di Garda or ; lmo, label=Eastern Lombard, Lach de Garda; vec, Ƚago de Garda; la, Benacus; grc, Βήνακος) is the largest lake in Italy.
It is a popular holiday location in northern Italy, about halfway between ...
.
Types of moraines
Moraines can be classified either by origin, location with respect to a glacier or former glacier, or by shape.
Lateral moraines
Lateral moraines are parallel ridges of debris deposited along the sides of a glacier. The unconsolidated debris can be deposited on top of the glacier by frost shattering
Frost weathering is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedg ...
of the valley walls or from tributary streams flowing into the valley, or may be subglacial debris carried to the surface of the glacier, melted out, and transported to the glacier margin.
Lateral moraines can rise up to over the valley floor, can be up to long, and are steeper close to the glacier margin (up to 80 degrees) than further away (where slopes are typically 29 to 36 degrees.[
]
Ground moraines
Ground moraines are till-covered areas with irregular topography and no ridges, often forming gently rolling hills or plains, with relief of less than . Ground moraine is accumulated at the base of the ice as lodgment till with a thin and discontinuous upper layer of supraglacial till deposited as the glacier retreats. It typically is found in the areas between end moraines.
Rogen moraines
Rogen moraines or ribbed moraines are a type of basal moraines that form a series of ribs perpendicular to the ice flow in an ice sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at Las ...
. The depressions between the ribs are sometimes filled with water, making the Rogen moraines look like tigerstripe
Tigerstripe is the name of a group of camouflage patterns developed for close-range use in dense jungle during jungle warfare by the South Vietnamese Armed Forces and adopted in late 1962 to early 1963 by US Special Forces during the Vietnam ...
s on aerial photograph
Aerial photography (or airborne imagery) is the taking of photographs from an aircraft or other airborne platforms. When taking motion pictures, it is also known as aerial videography.
Platforms for aerial photography include fixed-wing ai ...
s. Rogen moraines are named after Lake Rogen[Möller, P., 2006. Rogen moraine: an example of glacial reshaping of preexisting landforms. '']Quaternary Science Reviews
''Quaternary Science Reviews'' is a peer-reviewed scientific journal covering quaternary science. It was established in 1982 by Pergamon Press and is currently published by Elsevier. The editor-in-chief is C.V. Murray Wallace (University of Wollon ...
'', 25:362–389 in Härjedalen
Härjedalen (; no, Herjådalen or ) is a historical Provinces of Sweden, province (''landskap'') in the centre of Sweden. It borders the Norway, Norwegian county of Trøndelag as well as the provinces of Dalarna, Hälsingland, Medelpad, and Jä ...
, Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
, the landform's type locality.
de Geer moraines
Closely related to Rogen moraines, de Geer moraines are till ridges up to 5m high and 10-50m wide running perpendicular to the ice flow. They occur in large groups in low-lying areas. Named for Gerard de Geer, who first described them in 1889, these moraines may have developed from crevasses underneath the ice sheet. The Kvarken
Kvarken ( sv, Kvarken, Norra Kvarken (as opposed to South Kvarken); ) is the narrow region of the Gulf of Bothnia separating the Bothnian Bay (the inner part of the gulf) from the Bothnian Sea. The distance from the Swedish mainland to the Finn ...
has a very high density of de Geer moraines.
End or terminal moraines
End moraines, or terminal moraine
A terminal moraine, also called end moraine, is a type of moraine that forms at the terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed by the front edge ...
s, are ridges of unconsolidated debris deposited at the snout or end of the glacier. They usually reflect the shape of the glacier's terminus. Glaciers act much like a conveyor belt, carrying debris from the top of the glacier to the bottom where it deposits it in end moraines. End moraine size and shape are determined by whether the glacier is advancing, receding or at equilibrium. The longer the terminus of the glacier stays in one place, the more debris accumulate in the moraine. There are two types of end moraines: terminal and recessional. Terminal moraines mark the maximum advance of the glacier. Recessional moraines are small ridges left as a glacier pauses during its retreat. After a glacier retreats, the end moraine may be destroyed by postglacial erosion.
Recessional moraine
Recessional moraines are often observed as a series of transverse ridges running across a valley behind a terminal moraine. They form perpendicular to the lateral moraines that they reside between and are composed of unconsolidated debris deposited by the glacier. They are created during temporary halts in a glacier's retreat.
Arctic push moraines
In permafrost areas an advancing glacier may push up thick layers of frozen sediments at its front. An arctic push moraine will then be formed.
Medial moraine
A medial moraine is a ridge of moraine that runs down the center of a valley floor. It forms when two glaciers meet and the debris on the edges of the adjacent valley sides join and are carried on top of the enlarged glacier. As the glacier melts or retreats, the debris is deposited and a ridge down the middle of the valley floor is created. The Kaskawulsh Glacier in the Kluane National Park
Kluane National Park and Reserve (; french: Parc national et réserve de parc national de Kluane) are two protected areas in the southwest corner of the territory of Yukon. The National Park Reserve was set aside in 1972 to become a national par ...
, Yukon
Yukon (; ; formerly called Yukon Territory and also referred to as the Yukon) is the smallest and westernmost of Canada's three territories. It also is the second-least populated province or territory in Canada, with a population of 43,964 as ...
, has a ridge of medial moraine 1 km wide.
Supraglacial moraines
Supraglacial moraines are created by debris accumulated on top of glacial ice. This debris can accumulate due to ice flow toward the surface in the ablation zone
Ablation zone or ''ablation area'' refers to the low-altitude area of a glacier or ice sheet below firn with a net loss in ice mass due to melting, sublimation, evaporation, ice calving, aeolian processes like blowing snow, avalanche, and any oth ...
, melting of surface ice or from debris that falls onto the glacier from valley sidewalls.
Washboard moraines
Washboard moraines, also known as minor or corrugated moraines, are low-amplitude geomorphic features caused by glaciers. They consist of low-relief ridges, in height and around apart, accumulated at the base of the ice as lodgment till. The name "washboard moraine" refers to the fact that, from the air, it resembles a washboard.''
Veiki moraine
A Veiki moraine is a kind of hummocky moraine that forms irregular landscapes of ponds and plateaus surrounded by banks. It forms from the irregular melting of ice covered with a thick layer of debris. Veiki moraine is common in northern Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
and parts of Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
.
See also
; Geologic features related to moraines
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; Moraine examples
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References
Further reading
*
External links
"Glacial moraines unmistakable vestige of last ice age" – ''Pantagraph''
(Bloomington, Illinois newspaper)
{{Authority control
Glaciology
Sediments
Mountaineering
Geomorphology
Glacial landforms