Not to be confused withMurrain, an antiquated term for various infectious diseases affecting cattle and sheep.
The snow-free debris hills around the lagoon are lateral and terminal moraines of avalley glacier inManang, Nepal.
Amoraine is any accumulation of unconsolidated debris (regolith androck), sometimes referred to asglacial 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 calledglacial flour. Lateral moraines are those formed at the side of the ice flow, andterminal moraines are those formed at the foot, marking the maximum advance of the glacier. Other types of moraine include ground moraines (till-covered areas forming sheets on flat or irregulartopography) and medial moraines (moraines formed where two glaciers meet).
Moraines arelandforms composed ofglacial till deposited primarily by glacial ice.[2] Glacial till, in turn, isunstratified andunsorted debris ranging in size fromsilt-sizedglacial flour to large boulders.[3] The individual rock fragments are typically sub-angular to rounded in shape.[4] Moraines may be found on the glacier's surface or deposited as piles or sheets of debris where the glacier has melted.[5]
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.[6] Moraine forming processes may be loosely divided intopassive andactive.[7]
Passive processes involve the placing of chaotic supraglacial sediments onto the landscape with limited reworking, typically forminghummocky moraines.[8][9] These moraines are composed of supraglacial sediments from the ice surface.[7]
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 oftill and reworked proglacial sediment.[10]
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.[11] 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 ofplacer deposits ofgold as is the case ofsouthernmost Chile.[12]
Moraines can be classified either by origin, location with respect to a glacier or former glacier, or by shape.[13]The first approach is suitable for moraines associated with contemporary glaciers—but more difficult to apply toold moraines, which are defined by their particular morphology, since their origin is debated. Some moraine types are known only from ancient glaciers, while medial moraines of valley glaciers are poorly preserved and difficult to distinguish after the retreat or melting of the glacier.[citation needed]
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 byfrost shattering of the valley walls or from tributary streams flowing into the valley,[14] or may be subglacial debris carried to the surface of the glacier, melted out, and transported to the glacier margin.[15]
Moraines clearly seen on a side glacier of theGorner Glacier, Zermatt, Switzerland. Thelateral moraine is the high snow-free bank of debris in the top left hand quarter of the picture. Themedial moraine is the double line of debris running down the centre-line of the glacier.
Lateral moraines can rise up to 140 meters (460 ft) over the valley floor, can be up to 3 kilometers (1.9 mi) long, and are steeper close to the glacier margin (up to 80 degrees) than further away (where slopes are typically 29 to 36 degrees).[15]
Ground moraines are till-covered areas with irregular topography and no ridges, often forming gently rolling hills or plains,[16] with relief of less than 10 meters (33 ft). Ground moraine is accumulated at the base of the ice aslodgment 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.[17]
Rogen moraines or ribbed moraines are a type of basal moraines that form a series of ribs perpendicular to the ice flow in anice sheet. The depressions between the ribs are sometimes filled with water, making the Rogen moraines look liketigerstripes onaerial photographs. Rogen moraines are named afterLake Rogen[18] inHärjedalen,Sweden, the landform's type locality.
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.[19] Named forGerard De Geer, who first described them in 1889, these moraines may have developed from crevasses underneath the ice sheet.[19] TheKvarken has a very high density of de Geer moraines.[20]
Multiple erratics on theWithrow terminal moraine of the Okanogan Lobe. Cascade mountains in the background.
End moraines, orterminal moraines, are ridges of unconsolidated debris deposited at the snout or end of the glacier. They usually reflect the shape of theglacier'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.[21]
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.[6][22]
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. TheKaskawulsh Glacier in theKluane National Park,Yukon, has a ridge of medial moraine 1 km wide.[23]
The prominent dark streak at the left quarter is forming a medial moraine. This is seen as a mudflat at the water's surface. (Brüggen Glacier,Patagonia).
Supraglacial moraines are created by debris accumulated on top of glacial ice. This debris can accumulate due to ice flow toward the surface in theablation zone,[24] melting of surface ice[25] or from debris that falls onto the glacier from valley sidewalls.[26]
Washboard moraines, also known asminor orcorrugated moraines, are low-amplitude geomorphic features caused by glaciers. They consist of low-relief ridges, 1 to 2 meters (3 ft 3 in to 6 ft 7 in) in height and around 100 meters (330 ft) apart, accumulated at the base of the ice aslodgment till.[27] The name "washboard moraine" refers to the fact that, from the air, it resembles awashboard.
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 northernSweden and parts ofCanada.
^abJackson, Julia A., ed. (1997). "moraine [glac geol]".Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute.ISBN0922152349.
^Dreimanis, Aleksis (1989). "Tills: Their genetic terminology and classification". In Goldthwait; Matsch (eds.).Genetic classification of glacigenic deposits : final report of the Commission on Genesis and Lithology of Glacial Quaternary Deposits of the International Union for Quaternary Research (INQUA). Rotterdam: Balkema. pp. 17–83.ISBN9061916941.
^"Lateral Moraine".National Geographic Encyclopedia. May 5, 2011. RetrievedJune 18, 2020.
^abLukas, Sven; Graf, Andreas; Coray, Sandro; Schlüchter, Christian (March 2012). "Genesis, stability and preservation potential of large lateral moraines of Alpine valley glaciers – towards a unifying theory based on Findelengletscher, Switzerland".Quaternary Science Reviews.38:27–48.Bibcode:2012QSRv...38...27L.doi:10.1016/j.quascirev.2012.01.022.
^Möller, P., 2006. Rogen moraine: an example of glacial reshaping of preexisting landforms.Quaternary Science Reviews,25:362–389
^abMetsähallitus (Forest and Park Services) (16 July 2006).The Kvarken Archipelago(PDF) (Report). Retrieved3 October 2021.
^Kotilainen, Aarno T.; Kaskela, Anu M.; Bäck, Saara; Leinikki, Jouni (2012). "Submarine De Geer Moraines in the Kvarken Archipelago, the Baltic Sea".Seafloor Geomorphology as Benthic Habitat:289–298.doi:10.1016/B978-0-12-385140-6.00017-7.ISBN9780123851406.
^Loomis, S.R. (1970). "Morphology and structure of an ice-cored medial moraine, Kaskawulsh Glacier, Yukon".Arctic Institute of North America Research Paper.57:1–65.
^Stewart, Robert A.; Bryant, Deborah; Sweat, Michael J. (March 1988). "Nature and origin of corrugated ground moraine of the Des Moines lobe, Story County, Iowa".Geomorphology.1 (2):111–130.Bibcode:1988Geomo...1..111S.doi:10.1016/0169-555X(88)90010-4.
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