Temperate glaciers reach the pressure-melting point throughout, for at least for part of the year. Today, temperate glaciers are found in mild maritime climates such as southern Iceland, western Norway, New Zealand, and southern Chile, where both winter snowfall and summer melt rates are high.
Temperate glaciers are often very sensitive to changes in climate and will periodically advance (e.g. during the winter) even when in overall recession. This type of glacier is defined as active.
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The active temperate glacier landsystem reflects the wet-based thermal regime of temperate glaciers, and their tendency to oscillate in response to seasonal temperature. The landforms created by lowland temperate glaciers (such as those in southern Iceland) fall into three groups: ice marginal landforms, subglacial landforms, and glaciofluvial and glaciolacustrine landforms.
Landform assemblages of active temperate glaciers
Ice-marginal landforms
One of the most characteristic features of the active temperate glacier landsystem are the sharp, low relief moraine ridges found on their forelands1,2. These moraines are typically <10 m high and mimic the shape of the glacier snout when deposited, often taking on a saw-tooth pattern that reflects the pattern of ice-margin crevasses3.
These moraines are formed by a combination of ice pushing and the dumping of sediment from the snout. Some sediment may also be squeezed out from beneath an advancing snout (either during winter advance, or during the summer when sediment beneath the snout can become saturated with water and more mobile).
Because active temperate glaciers often advance during winter and retreat during summer, a series of annual push moraines can form during deglaciation4-6.
Subglacial landforms
The beds of former active temperate glaciers are characterised by landforms of both erosion and deposition1,2.
Where exposed at the land surface, bedrock is polished, moulded and striated. The bedrock may also be shaped into roches moutonnées, indicating that both abrasion and quarrying occur at active temperate glacier beds.
Streamlined subglacial landforms, such as flutes and drumlins, are also common on temperate glacier forelands1,7. These features form in large groups at right angles to push moraines (i.e. in the direction of former glacier flow) by some combination of subglacial deformation8,9 and the ploughing (erosion) of soft sediments by the overriding glacier10.
Temperate glacier forelands sometimes contain overridden moraines1,2, which are more subdued than push moraines and have flutes across their surfaces. These serve as evidence for ice-overriding during a glacier advance.
Glaciofluvial and glaciolacustrine landforms
While not unique to the active temperate glacier landsystem, glaciofluvial and glaciolacustrine landforms are common owing to the high volumes of meltwater released by temperate glaciers during the spring and summer months1,2.
Proglacial streams that flow away from the snout produce outwash (also referred to as sandur) fans11, whereas meltwater draining around the sides of the glacier form kame terraces and narrow outwash corridors1,2.
As sandur fans form in contact with the snout, they often develop ‘pitted’ surfaces where glacial ice is buried and later melts out, leaving small lakes at the outwash surface1,2.
Some temperate glacier forelands also contain eskers, which are narrow, often sinuous ridges of glaciofluvial sand and gravel that form in subglacial, englacial and supraglacial (all ice-walled) channels, which give some indication of the patterns of meltwater drainage in former glaciers12.
Ice-dammed or proglacial lakes are commonly found around the margins of receding temperate glaciers. These lakes interrupt the path of sediment-containing meltwater streams, allowing thick sequences of sediment to accumulate at the lake bottom1,2. Lake shorelines and deltas also form around glacial lake margins and often remain clear in the landscape after a lake has drained1.2.
The active temperate glacier landsystem
The active temperate glacier landsystem1,2 serves as a clear and detailed signature of past glacial activity, particularly of ice-front oscillations and meltwater drainage patterns.
Research has shown that active temperate glaciers existed in a wide range of formerly glaciated regions. For example, some Ice Age (around 20,000 years ago) glaciers of the Laurentide13 and Patagonian ice sheets14 and the New Zealand mountain ice cap15 produced landform assemblages typical of active temperate glacier activity.
Because the behaviour (e.g. seasonal advance and retreat patterns) of active temperate glaciers is closely tied to climate, identifying their landsystem in formerly glaciated areas can serve as a record of past climate.
In summary, the active temperate glacier landsystem1,2 usually contains: large areas of low amplitude push, dump and squeeze moraines (that mark out former glacier positions), which often record active annual recession; flutes, drumlins, and ice-moulded bedrock between moraine ridges; and extensive glaciofluvial (outwash, eskers, kame terraces) and glaciolacustrine (shorelines) features that provide evidence of abundant meltwater around the glacier snout.