Moraine
Accumulation of glacial debris carried by ice.
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 down to gravel and sand, in a groundmass of finely divided clayey material sometimes called glacial flour. Moraines are landforms composed of glacial till deposited primarily by glacial ice, and they may be found on the glacier's surface or deposited as piles or sheets of debris where the glacier has melted.
- field
- Geology
- known_for
- Accumulations of glacial till forming various landforms such as lateral, terminal, and medial moraines
- etymology
- Borrowed from French moraine, derived from Savoyard Italian morena ('mound of earth'), introduced into geology by Horace Bénédict de Saussure in 1779
Lore & Background
The word moraine is borrowed from French moraine, 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'). The term was introduced into geology by Horace Bénédict de Saussure in 1779. 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. Active processes form or rework moraine sediment directly by the movement of ice, known as glaciotectonism, forming push moraines and thrust-block moraines. Moraines can be classified either by origin, location with respect to a glacier or former glacier, or by shape. Types include lateral moraines, ground moraines, Rogen moraines, de Geer moraines, end or terminal moraines, recessional moraines, arctic push moraines, medial moraines, supraglacial moraines, washboard moraines, and Veiki moraines. 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.
Reader's Guide
Moraines are significant as primary landforms that record the history and dynamics of glaciers and ice sheets. They provide evidence of past glacial extents, as terminal moraines mark the maximum advance of a glacier, while recessional moraines indicate pauses during retreat. The study of moraines helps geologists understand glacial processes, climate change, and landscape evolution. Rogen moraines and de Geer moraines, with their distinctive ribbed patterns perpendicular to ice flow, offer insights into ice sheet behavior. The reworking of moraines may lead to the formation of placer deposits of gold, as is the case of southernmost Chile. Moraines also influence modern landscapes and ecosystems, as seen in examples like the Oak Ridges Moraine in Canada and the Kettle Moraine in Wisconsin. The term's introduction by Horace Bénédict de Saussure in 1779 marks a foundational moment in glacial geology.
Did You Know?
- The word moraine is borrowed from French moraine, derived from Savoyard Italian morena ('mound of earth'), and was introduced into geology by Horace Bénédict de Saussure in 1779.
- Rogen moraines are named after Lake Rogen in Härjedalen, Sweden, the landform's type locality.
- Reworking of moraines may lead to the formation of placer deposits of gold, as is the case of southernmost Chile.
Frequently Asked Questions
What is a Moraine in geology?
A moraine is a pile or sheet of unconsolidated glacial debris—ranging from boulders down to fine clayey material—that was transported and deposited by a glacier or ice sheet. These landforms can appear on the surface of an active glacier or left behind in formerly glaciated terrain.
What types of Moraines are there?
The main varieties are lateral moraines (ridges along a glacier's sides), terminal moraines (debris piles marking the glacier's farthest advance), and medial moraines (strips forming where two glaciers merge and their side debris converge).
What is a Moraine made of?
Moraine material is essentially glacial till: a mix of partly rounded rock fragments, gravel, and sand set in a matrix of very fine clayey particles sometimes called glacial flour. Because the debris is unsorted and unconsolidated, boulders and silt can sit side by side with no layering.
Where does the word 'Moraine' come from?
The term was borrowed from French and traces back to the Savoyard Italian word 'morena,' meaning a mound of earth. Swiss naturalist Horace Bénédict de Saussure introduced it into formal geological usage in 1779.
Why do geologists care about Moraines?
Moraines serve as visible records of past ice extent and movement, helping scientists reconstruct glacial history and understand how ice sheets shaped landscapes. Their composition and position also provide clues about the speed, direction, and duration of ancient glaciation.
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