The vertical distance between any two surfaces, and in particular between the glacier face and the summer surface, or the glacier surface and the bed. Glacier thickness is measured ideally by interpol
ating from a dense array of point measurements, constructed for example from ground-penetrating radar traverses. However the measurement density is often less than ideal, as when the array consists of a single traverse or even just a small number of boreholes. On most glaciers there are no thickness measurements at all and the thickness must be estimated, for example by volume-area scaling or as a function of surface slope and estimated basal shear stress. The definition of thickness as a vertical distance is adopted almost invariably in studies of mass balance, but not in all branches of cryospheric science. For example Fierz et al. (2009) define thickness as the coordinate normal to the slope, measured from the base of a layer of snow.
The change in the thickness of the glacier at a defined horizontal location. Thickness can change at a point due to ablation and accumulation at the surface and bottom of the glacier, compaction of sn
ow and firn, or a non-zero emergence velocity or submergence velocity. Thickness change is often used interchangeably with elevation change, but the two are not necessarily the same. For example, elevation can change due to glacial isostatic adjustment or vertical tectonic motions, without a change in glacier thickness. The thickness change at a point is not equivalent to the climatic-basal mass balance at that point because the thickness change may be due in part to emergence or submergence. Thickness change at a point is therefore not a direct indicator of the local climate. The glacier-wide mean thickness change is the volume change of the entire glacier divided by the mean glacier area during the time span of the measurements: 2(h V VS S 21)/(21) , where V is volume, S is area, and subscripts 1 and 2 refer to measurements at an earlier and later time, respectively. The quantity 21( ) V V V is the volume change. Usually the two volumes are not known separately, and: V is obtained from measurements of by geodetic methods. The mean thickness change, if multiplied by the density of the mass gained or lost, is equal to the glacier-wide mass balance over the period of the thickness change. The mean thickness change differs from the change of mean thickness, which is V2/S2 V1/S1.
First-year ice 30-70 cm thick. May be subdivided into thin first-year ice of the first stage 30 to 50 cm thick and thin first-year ice of the second stage 50 to 70 cm.
An entity, situation, association, or event that may be perceived, known, or imagined. Equivalent to Entity of Sowa (2000). Top concept in this domain of discourse.
The mass flux through a vertical cross section corresponding to the decrease of mass upglacier from the section (that is, the integral of density over the thickness of the glacier and the upglacier ar
ea).