moraine
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A moraine is any accumulation of unconsolidated debris (
regolith Regolith () is a blanket of unconsolidated, loose, Homogeneity and heterogeneity, heterogeneous superficial deposits covering solid Rock (geology), rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moo ...

regolith
and
rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition and the way in w ...
), 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 Silt is granular material of a size between sand Sand is a granular material composed of finely divided rock and mineral particles. Sand has various compositions but is defined ...
. 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 Glacier terminus, terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed b ...
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 di ...

till
-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 could refer to the surface forms and features themselves, or a description (especially their depiction in maps). Topography is a field of geoscience ...
) and medial moraines (moraines formed where two glaciers meet).


Etymology

The word ''moraine'' is derived from the French root (), which in turn is derived from the Savoyard Italian . The term was introduced into geology by Horace Bénédict de Saussure in 1779.


Characteristics

Moraines are
landforms A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws o ...
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 di ...
deposited primarily by glacial ice. Glacial till, in turn, is unstratified and unsorted debris ranging in size from silt-sized Rock flour, glacial flour 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 hummocky 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 di ...

till
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 deposits of gold as is the case of Magallanes Region, southernmost Chile. File:Ansel Adams - National Archives 79-AA-M02.jpg, Moraine in Rocky Mountain National Park, taken by Ansel Adams in 1941. File:Icy-lake.jpg, Moraines around the Icy lake (2709 m), just below Musala peak (2925 m) in Rila, Rila Mountain, Bulgaria. File:Moraines Surlej.jpg, Lateral moraines of a retreating glacier in Engadin. File:Colline moreniche del Lago Garda.JPG, Moraine of Lake Garda.


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 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 Till#Types of Till, 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. 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 RogenMöller, P., 2006. Rogen moraine: an example of glacial reshaping of preexisting landforms. ''Quaternary Science Reviews'', 25:362–389 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. Named for Gerard de Geer, who first described them in 1889, these moraines may have developed from crevasses underneath the ice sheet. The Kvarken Archipelago, Kvarken has a very high density of de Geer moraines.


End or terminal moraines

Image:Erratics-Cascades-PB110028.JPG, left, Multiple erratics on the terminal moraine of the Okanogan Lobe. Cascade mountains in the background. End moraines, or
terminal moraine A terminal moraine, also called end moraine, is a type of moraine that forms at the Glacier terminus, terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed b ...
s, are ridges of unconsolidated debris deposited at the snout or end of the glacier. They usually reflect the shape of the Glacier terminus, 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.


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, Yukon, 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, 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 Till#Types of Till, lodgment till. The name "washboard moraine" refers to the fact that, from the air, it resembles a washboard (laundry), 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 :* :* :* :* :* :* ; Moraine examples :* :* :* :* :* :* :*


References


Further reading

*


External links


"Glacial moraines unmistakable vestige of last ice age" – ''Pantagraph''
(Bloomington, Illinois newspaper) {{Authority control Glaciology Sediments Moraines, Mountaineering Geomorphology Glacial landforms