Moraine

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The snow-free debris hills around the lagoon are lateral and terminal moraines of a valley glacier in Nepal. Manang site (54).JPG
The snow-free debris hills around the lagoon are lateral and terminal moraines of a valley glacier in Nepal.

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 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. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were 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 irregular topography) and medial moraines (moraines formed where two glaciers meet).

Contents

Etymology

The word moraine is borrowed from French moraine [mɔ.ʁɛn] , which in turn is derived from the Savoyard Italian morena ("mound of earth"). Morena in this case was derived from Provençal morre ("snout"), itself from Vulgar Latin *murrum "rounded object". [1] The term was introduced into geology by Horace Bénédict de Saussure in 1779. [2]

Characteristics

Moraines are landforms composed of glacial till deposited primarily by glacial ice. [2] Glacial till, in turn, is unstratified and unsorted debris ranging in size from silt-sized glacial 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]

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. [6] Moraine forming processes may be loosely divided into passive and active. [7]

Passive processes involve the placing of chaotic supraglacial sediments onto the landscape with limited reworking, typically forming hummocky 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 of till 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 of placer deposits of gold as is the case of southernmost Chile. [12]

Types of moraines

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 to old 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

Lateral moraines above Lake Louise, Alberta, Canada. MorainesLakeLouise.JPG
Lateral moraines above Lake Louise, Alberta, Canada.

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 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 the Gorner Glacier, Zermatt, Switzerland. The lateral moraine is the high snow-free bank of debris in the top left hand quarter of the picture. The medial moraine is the double line of debris running down the centre-line of the glacier. Glacier.zermatt.arp.750pix.jpg
Moraines clearly seen on a side glacier of the Gorner Glacier, Zermatt, Switzerland. The lateral moraine is the high snow-free bank of debris in the top left hand quarter of the picture. The medial 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

Ground moraines create irregular, rolling topography. Ground moraine 9004.jpg
Ground moraines create irregular, rolling topography.

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 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. [17]

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. The depressions between the ribs are sometimes filled with water, making the Rogen moraines look like tigerstripes on aerial photographs. Rogen moraines are named after Lake Rogen [18] in Härjedalen, Sweden, 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. [19] Named for Gerard de Geer, who first described them in 1889, these moraines may have developed from crevasses underneath the ice sheet. [19] The Kvarken has a very high density of de Geer moraines. [20]

End or terminal moraines

Multiple erratics on the terminal moraine of the Okanogan Lobe. Cascade mountains in the background. Erratics-Cascades-PB110028.JPG
Multiple erratics on the terminal moraine of the Okanogan Lobe. Cascade mountains in the background.

End moraines, or terminal moraines, 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. [21]

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. [6] [22]

Medial moraine

Medial moraines, Nuussuaq Peninsula, Greenland. Nuussuaq-peninsula-moraines.jpg
Medial moraines, Nuussuaq Peninsula, Greenland.

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, Yukon, has a ridge of medial moraine 1 km wide. [23]

Bruggen-PioXI FaceCompleteCroppedIMG5642.jpg
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

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, [24] melting of surface ice [25] or from debris that falls onto the glacier from valley sidewalls. [26]

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, 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 as lodgment till. [27] 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 and parts of Canada.

See also

Geologic features related to moraines
  • Glacial landform   Landform created by the action of glaciers
  • Drumlin   Geological feature formed by glacial ice acting on underlying unconsolidated till or ground moraine
  • Esker   Long, winding ridge of stratified sand and gravel associated with former glaciers
  • Moraine-dammed lake   Type of lake formed by glaciation
  • Terminal moraine   Type of moraine that forms at the terminal of a glacier
  • Rogen moraine   Landform of ridges deposited by a glacier or ice sheet transverse to ice flow
Moraine examples

Related Research Articles

<span class="mw-page-title-main">Glacier</span> Persistent body of ice that is moving under its own weight

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 over many years, often centuries. It acquires distinguishing features, such as crevasses and seracs, as it slowly flows and deforms under stresses induced by its weight. As it moves, it abrades rock and debris from its substrate to create landforms such as cirques, moraines, or fjords. Although a glacier may flow into a body of water, it forms only on land and is distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.

<span class="mw-page-title-main">Drumlin</span> Geological feature formed by glacial ice acting on underlying unconsolidated till or ground moraine

A drumlin, from the Irish word droimnín, first recorded in 1833, in the classical sense is an elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine. Assemblages of drumlins are referred to as fields or swarms; they can create a landscape which is often described as having a 'basket of eggs topography'.

<span class="mw-page-title-main">Till</span> Unsorted glacial sediment

Till or glacial till is unsorted glacial sediment.

<span class="mw-page-title-main">Esker</span> Long, winding ridge of stratified sand and gravel associated with former glaciers

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 America. Eskers are frequently several kilometres long and, because of their uniform shape, look like railway embankments.

Landforms are categorized by characteristic physical attributes such as their creating process, shape, elevation, slope, orientation, rock exposure, and soil type.

A kame delta is a glacial landform formed by a stream of melt water flowing through or around a glacier and depositing material, known as kame deposits. Upon entering a proglacial lake at the end (terminus) of a glacier, the river/stream deposit these sediments. This landform can be observed after the glacier has melted and the delta's asymmetrical triangular shape is visible. Once the glacier melts, the edges of the delta may subside as ice under it melts. Glacial till is deposited on the lateral sides of the delta, as the glacier melts.

<span class="mw-page-title-main">Glacial erratic</span> Piece of rock that has been moved by a glacier

A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word errare, are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock in Alberta.

<span class="mw-page-title-main">Till plain</span> 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. Till plains created by the Wisconsin glaciation cover much of the Midwest, including North Dakota, South Dakota, Indiana, Minnesota, Wisconsin, Iowa, Illinois, and northern Ohio.

<span class="mw-page-title-main">Glacial landform</span> Landform created by the action of glaciers

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

<span class="mw-page-title-main">Glacial lake</span> Lake formed by a melted glacier

A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land and then melts, filling the depression created by the glacier.

The Oak Ridges Moraine is a geological landform that runs east-west across south central Ontario, Canada. It developed about 12,000 years ago, during the Wisconsin glaciation in North America. A complex ridge of sedimentary material, the moraine is known to have partially developed under water. The Niagara Escarpment played a key role in forming the moraine in that it acted as a dam for glacial meltwater trapped between it and two ice lobes.

<span class="mw-page-title-main">Terminal moraine</span> Type of moraine that forms at the terminal of a glacier

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 of the ice, is driven no further and instead is deposited in an unsorted pile of sediment. Because the glacier acts very much like a conveyor belt, the longer it stays in one place, the greater the amount of material that will be deposited. The moraine is left as the marking point of the terminal extent of the ice.

Fluvio refers to things related to rivers and glacial refers to something that is of ice. Fluvio-glacial refers to the meltwater created when a glacier melts. Fluvio-glacial processes can occur on the surface and within the glacier. The deposits that happen within the glacier are revealed after the entire glacier melts or partially retreats. Fluvio-glacial landforms and erosional surfaces include: outwash plains, kames, kame terraces, kettle holes, eskers, varves, and proglacial lakes.

<span class="mw-page-title-main">Tunnel valley</span> Glacial-formed geographic feature

A tunnel valley is a U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages. They can be as long as 100 km (62 mi), 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep.

<span class="mw-page-title-main">Rogen moraine</span> Landform of ridges deposited by a glacier or ice sheet transverse to ice flow

A Rogen moraine is a subglacially formed type of moraine landform, that mainly occurs in Fennoscandia, Scotland, Ireland and Canada. It is one of the three main types of hummocky moraines. They cover large areas that have been covered by ice, and occur mostly in what is believed to have been the central areas of the ice sheets. Rogen moraines are named after Lake Rogen in Härjedalen, Sweden, the landform's type locality. Rogen Nature Reserve serves to protect the unusual area.

A subaqueous fan is a fan-shaped deposit formed beneath water, and are commonly related to glaciers and crater lakes.

Fluvioglacial landforms are those that result from the associated erosion and deposition of sediments caused by glacial meltwater. These landforms may also be referred to as glaciofluvial in nature. Glaciers contain suspended sediment loads, much of which is initially picked up from the underlying landmass. Landforms are shaped by glacial erosion through processes such as glacial quarrying, abrasion, and meltwater. Glacial meltwater contributes to the erosion of bedrock through both mechanical and chemical processes.

<span class="mw-page-title-main">Supraglacial lake</span> Pond of liquid water on the top of a glacier

A supraglacial lake is any pond of liquid water on the top of a glacier. Although these pools are ephemeral, they may reach kilometers in diameter and be several meters deep. They may last for months or even decades at a time, but can empty in the course of hours.

The glacial series refers to a particular sequence of landforms in Central Europe that were formed during the Pleistocene glaciation beneath the ice sheets, along their margins and on their forelands during each glacial advance.

<span class="mw-page-title-main">Glaciofluvial deposits</span> Sediments/deposits formed from ice sheets or glaciers

Glaciofluvial deposits or Glacio-fluvial sediments consist of boulders, gravel, sand, silt and clay from ice sheets or glaciers. They are transported, sorted and deposited by streams of water. The deposits are formed beside, below or downstream from the ice. They include kames, kame terraces and eskers formed in ice contact and outwash fans and outwash plains below the ice margin. Typically the outwash sediment is carried by fast and turbulent fluvio-glacial meltwater streams, but occasionally it is carried by catastrophic outburst floods. Larger elements such as boulders and gravel are deposited nearer to the ice margin, while finer elements are carried farther, sometimes into lakes or the ocean. The sediments are sorted by fluvial processes. They differ from glacial till, which is moved and deposited by the ice of the glacier, and is unsorted.

References

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Further reading

  • Easterbrook, D. J. (1999), Surface processes and landforms (Second ed.), Upper Saddle River, N.J.: Prentice Hall, ISBN   9780138609580