The removal of ice by melting at the base of a glacier. At the base of grounded temperate ice, melting is either fuelled by the geothermal heat flux and the conversion of the kinetic energy of basal s
liding to heat, or results from variations of the pressure-melting point. Pressure melting, however, tends to be balanced by regelation. Typical continental geothermal heat fluxes G of 0.050.15 W m-2 imply potential basal ablation G/Lf of 514 mm w. E. A-1, where Lf is the latent heat of fusion. Much greater geothermal heat fluxes are found in areas of Active volcanism. If all of the energy of basal sliding is converted to heat, basal ablation ubb/Lf at rates of 330 mm w. E. A-1 is implied by sliding velocities ub of 10100 m a-1 and basal shear stress b of 105 Pa. Basal ablation rates tens or hundreds of times greater are implied beneath ice streams. At the base of an ice shelf or floating tongue, melting occurs because of convection of warmer sea water to the ice-water interface, supplying the required latent heat of fusion. The rate of melting depends on the temperature of the sea water and the efficiency of the heat transfer between the seawater and the base of the ice shelf. Basal ablation rates beneath ice shelves or floating tongues can reach tens of m w. E. A-1, equivalent to heat transfer at hundreds of W m-2.
The freezing of water to the base of the glacier, increasing the mass of the glacier and Antarctic Ice Sheeting its basal temperature if that temperature is below the freezing point. The result of bas
al accumulation is typically observable in ice cores or at glacier margins as accreted ice that is relatively clear, often with some concentration of dispersed sediments incorporated from the glacier bed during freezing. Accreted ice may also be distinguishable from glacier ice (the latter sometimes referred to as meteoric ice in this context) by differences in isotopic content, geochemical composition and optical properties, and may have distinctive dielectric properties by which it can be recognized in ground-penetrating radar records. Accreted ice at the base of an ice shelf is referred to as marine ice. For purposes of the glaciological method, basal accumulation is indistinguishable from internal accumulation in that both represent addition of mass to the glacier that goes unaccounted for by surface observations.
The layer of ice at the bed of a glacier that is the product of melting and refreezing (regelation, q.v.). It is strongly layered, sheared and incorporates a variable amount of debris.
Reduction of friction at the base of an ice sheet or glacier due to lubrication by meltwater. This can allow the glacier or ice sheet to slide over its base. Meltwater may be produced by pressureinduc
ed melting, friction or geothermal heat, or surface melt may drain to the base through holes in the ice.
Basalt is the most common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystal
s in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey. On Earth, most basalt magmas have formed by decompression melting of the mantle. [Wikipedia]
A data encoding scheme whereby binary-encodeddata is converted to printable ASCII characters. It is defined as a MIMEcontent transfer encoding for use in Internet e-mail. The only charactersused are t
he upper- and lower-case Roman alphabet characters (A-Z, a-z), thenumerals (0-9), and the "+" and "/" symbols, with the "=" symbol as aspecial suffix (padding) code.