Glaciers
43
of great mountains. In Antarctica air temperatures of -89.2~ have been recorded;
warmer temperatures of - 30~ are reached as well, but temperatures increase with depth
as a result of the geothermal heat and of the internal deformation of the ice mass in the
glacier flow (Sugden, 1982).
Warm ice is formed when sufficient heat to produce melting is available. During
summer, melting of surface ice is common. This water percolates into the ice mass and can
freeze again, releasing its latent heat and by each gram of refrozen water elevating 160 g of
ice by 1 ~ This can be one of the most important heat sources. In these circumstances the
whole warm-ice glacier can be formed by ice at its pressure-melting point. At the ice base
geothermal heat is usually sufficient to elevate the temperature of the ice to its melting
point. This warm ice can also be at the bottom of glaciers whose superficial layers are of
cold ice (Budd et al., 1970).
These ice types allow differentiation of polar, or cold-based, and temperate or warmbased glaciers. These classifications are very simplistic, because the thermal conditions
of glaciers can vary in space and time (Sugden, 1977; Paterson, 1994), so that polythermal
ice is becoming increasingly recognized. Antarctica is dominantly a polar or cold-based
glacier, but some parts have warm ice at their base. In temperate glaciers the transformation of firn into ice is faster than in polar glaciers. These differences in ice temperature
are of extraordinary importance in glacial geomorphology and mainly related to the
presence of a thin water film in temperate glaciers lubricating the bed of the glacier and
facilitating its movement. At the same time this subglacial water facilitates quite important
erosive and sedimentation work.
5.2. Morphologic classification
Morphologic classifications are based upon geometry, position and size of the ice masses.
Some ice accumulations are restricted by the topography, whereas others do not present
any type of confinement. Continental ice sheets are represented by those of Antarctica
(Fig. 2.8) and Greenland. They show a domal form with a convex surface produced by
the ice flow. In the centre, ice accumulation thickness is larger and towards the margins
the surface slopes smoothly, increasing its gradient progressively and with diminishing
thickness. These ice sheets preserve or fossilize the underlying topography, although in
some cases the relief of the bedrock substrate exceeds that of the ice mass, and the rock
outcrops protrude through the ice as nunataks (Fig. 2.9).
Ice shelves (Fig. 2.10) are great masses that extend out into the sea > 500,000 km 2,
like the Ross and Filchner-Ronne ice shelves in Antarctica that occupy great bays and
have extensions corresponding to 7 per cent of the ice sheet. The ice thickness can reach
up to 200 m and the cliffs up to 30 m with the loosening of icebergs (Fig. 2.11) and
melting of its base. These floating ice masses contain particles of different sizes that fall
to the bottom of the sea when the ice melts (dropstones) (Fig. 2.12). On the ocean
surface remains a floating mass of split and rather thinner ice, denoted as pack ice
(Fig. 2.13). If the size of ice domes is smaller than 50,000 km 2 (Sugden and John, 1976)
they are denoted as mountain, plateau or plain ice caps, according to their topographic
position. The first is located on a plateau zone (Fig. 2.14), being the ice cap of
43
of great mountains. In Antarctica air temperatures of -89.2~ have been recorded;
warmer temperatures of - 30~ are reached as well, but temperatures increase with depth
as a result of the geothermal heat and of the internal deformation of the ice mass in the
glacier flow (Sugden, 1982).
Warm ice is formed when sufficient heat to produce melting is available. During
summer, melting of surface ice is common. This water percolates into the ice mass and can
freeze again, releasing its latent heat and by each gram of refrozen water elevating 160 g of
ice by 1 ~ This can be one of the most important heat sources. In these circumstances the
whole warm-ice glacier can be formed by ice at its pressure-melting point. At the ice base
geothermal heat is usually sufficient to elevate the temperature of the ice to its melting
point. This warm ice can also be at the bottom of glaciers whose superficial layers are of
cold ice (Budd et al., 1970).
These ice types allow differentiation of polar, or cold-based, and temperate or warmbased glaciers. These classifications are very simplistic, because the thermal conditions
of glaciers can vary in space and time (Sugden, 1977; Paterson, 1994), so that polythermal
ice is becoming increasingly recognized. Antarctica is dominantly a polar or cold-based
glacier, but some parts have warm ice at their base. In temperate glaciers the transformation of firn into ice is faster than in polar glaciers. These differences in ice temperature
are of extraordinary importance in glacial geomorphology and mainly related to the
presence of a thin water film in temperate glaciers lubricating the bed of the glacier and
facilitating its movement. At the same time this subglacial water facilitates quite important
erosive and sedimentation work.
5.2. Morphologic classification
Morphologic classifications are based upon geometry, position and size of the ice masses.
Some ice accumulations are restricted by the topography, whereas others do not present
any type of confinement. Continental ice sheets are represented by those of Antarctica
(Fig. 2.8) and Greenland. They show a domal form with a convex surface produced by
the ice flow. In the centre, ice accumulation thickness is larger and towards the margins
the surface slopes smoothly, increasing its gradient progressively and with diminishing
thickness. These ice sheets preserve or fossilize the underlying topography, although in
some cases the relief of the bedrock substrate exceeds that of the ice mass, and the rock
outcrops protrude through the ice as nunataks (Fig. 2.9).
Ice shelves (Fig. 2.10) are great masses that extend out into the sea > 500,000 km 2,
like the Ross and Filchner-Ronne ice shelves in Antarctica that occupy great bays and
have extensions corresponding to 7 per cent of the ice sheet. The ice thickness can reach
up to 200 m and the cliffs up to 30 m with the loosening of icebergs (Fig. 2.11) and
melting of its base. These floating ice masses contain particles of different sizes that fall
to the bottom of the sea when the ice melts (dropstones) (Fig. 2.12). On the ocean
surface remains a floating mass of split and rather thinner ice, denoted as pack ice
(Fig. 2.13). If the size of ice domes is smaller than 50,000 km 2 (Sugden and John, 1976)
they are denoted as mountain, plateau or plain ice caps, according to their topographic
position. The first is located on a plateau zone (Fig. 2.14), being the ice cap of