Chapter 5
Fluvioglacial erosion and sedimentation
1. The melt waters
The waters resulting from ice melt are a significant part of the glacial system and are the main
product of glacier ablation (Figure 5.1). The importance of melt water on the velocity of
glacier movement and on particle flow in a subglacial environment has already been
discussed. Furthermore, its important erosive and depositional role must be added, especially
downstream from the ice masses, where it can cause rapid changes in the drainage network
(Price, 1980) (Figure 5.2). Ice melt increases from the equilibrium line and reaches a
maximum in the more distal parts of the glacier. Here the fluvioglacial subsystem overlaps
the glacial one, in such a manner that the latter losses its predominance against the
fluvioglacial processes in the final parts of the ice mass (Sugden and John, 1976).
Melt waters can have a surface or an internal origin, the former being much more
important. The proportion of the surface ice melt diminishes with altitude, as other sources
increase: summer rainstorms, contributions from tributaries and groundwaters (Benn
and Evans, 1998). The basal and internal water derives from geothermal heat that, as an
average, is able to melt annually an ice sheet of--~6 mm thickness. The basal sliding
and deformation also produce heat and can cause the melting of a layer of 10 to 15 mm
thickness (Walder, 1982). Ice melt is maximum in temperate seacoast environments, and
diminishes in the high latitudes and in the interior of continents.
Ice melt results in channel developments (Figure 5.3) that occupy very diverse
positions inside and out of the ice masses, and even can pass through different
environments (Brodzikowski and Van Loon, 1991). According to the thermal regime, the
water can flow over the surface or in within the glacier. The size of the channels can range
from metric to kilometric scales. In marginal (Figure 5.4) and submarginal channels, melt
waters flow along the contact between the ice mass and the rocky hillslope, and can occupy
a lateral or frontal position in relation to the glacier. They are short, rarely exceeding 2 km
in length. Supraglacial channels reach a great development over the ice sheets, with
dendriform networks (Ferguson, 1973). The channels are straight or meandering, with
depths ranging between a few centimetres to a few metres (Figure 5.5). Their waters can
occasionally disappear into crevasses that progressively enlarge, becoming cylindrical
pools called moulins, with a glacial karstic topography (Stenborg, 1970).
The system of intraglacial and subglacial channels (Figure 5.6) reflects an internal
drainage, similar to that of soluble rocks, with large corridors and englacial lakes
(Figure 5.3 and Figure 5.7). This series of internal pipes is originated by ice melt, whereas
in karstic bedrock they develop by dissolution. The section of the pipes is circular if they
develop by forced or phreatic flow, and vertical-elongate if the flow is vadose or free. The
enlargement of the internal pipe network occurs mostly in summer, as a consequence of
Fluvioglacial erosion and sedimentation
1. The melt waters
The waters resulting from ice melt are a significant part of the glacial system and are the main
product of glacier ablation (Figure 5.1). The importance of melt water on the velocity of
glacier movement and on particle flow in a subglacial environment has already been
discussed. Furthermore, its important erosive and depositional role must be added, especially
downstream from the ice masses, where it can cause rapid changes in the drainage network
(Price, 1980) (Figure 5.2). Ice melt increases from the equilibrium line and reaches a
maximum in the more distal parts of the glacier. Here the fluvioglacial subsystem overlaps
the glacial one, in such a manner that the latter losses its predominance against the
fluvioglacial processes in the final parts of the ice mass (Sugden and John, 1976).
Melt waters can have a surface or an internal origin, the former being much more
important. The proportion of the surface ice melt diminishes with altitude, as other sources
increase: summer rainstorms, contributions from tributaries and groundwaters (Benn
and Evans, 1998). The basal and internal water derives from geothermal heat that, as an
average, is able to melt annually an ice sheet of--~6 mm thickness. The basal sliding
and deformation also produce heat and can cause the melting of a layer of 10 to 15 mm
thickness (Walder, 1982). Ice melt is maximum in temperate seacoast environments, and
diminishes in the high latitudes and in the interior of continents.
Ice melt results in channel developments (Figure 5.3) that occupy very diverse
positions inside and out of the ice masses, and even can pass through different
environments (Brodzikowski and Van Loon, 1991). According to the thermal regime, the
water can flow over the surface or in within the glacier. The size of the channels can range
from metric to kilometric scales. In marginal (Figure 5.4) and submarginal channels, melt
waters flow along the contact between the ice mass and the rocky hillslope, and can occupy
a lateral or frontal position in relation to the glacier. They are short, rarely exceeding 2 km
in length. Supraglacial channels reach a great development over the ice sheets, with
dendriform networks (Ferguson, 1973). The channels are straight or meandering, with
depths ranging between a few centimetres to a few metres (Figure 5.5). Their waters can
occasionally disappear into crevasses that progressively enlarge, becoming cylindrical
pools called moulins, with a glacial karstic topography (Stenborg, 1970).
The system of intraglacial and subglacial channels (Figure 5.6) reflects an internal
drainage, similar to that of soluble rocks, with large corridors and englacial lakes
(Figure 5.3 and Figure 5.7). This series of internal pipes is originated by ice melt, whereas
in karstic bedrock they develop by dissolution. The section of the pipes is circular if they
develop by forced or phreatic flow, and vertical-elongate if the flow is vadose or free. The
enlargement of the internal pipe network occurs mostly in summer, as a consequence of