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QR Code JIS X 0510 for .NET The velocity eld in a glacier in .NET Implementation Code 3/9 in .NET The velocity eld in a glacier

The velocity eld in a glacier use none none integration todisplay none on nonecreating qr code .net is stiffer than that a none none t the surface. Consequently, the vertical velocity generally decreases more rapidly beneath the divide than it does on the anks (Figure 5.9), so as layers form at the surface and are buried by subsequent accumulation, they are draped over the stiffer plug.

Because this explanation is based on Raymond s (1983) analysis of the vertical velocity eld (Equations (5.24) and (5.25)), the resulting distortion of the internal layering has become known as the Raymond bump.

Alternatively, drifting or wind scouring may reduce the accumulation over the divide, in which case the ow eld would have to adjust so that ws was lower there. Thus, again, isochronous surfaces would be buried less rapidly beneath the divide than on the anks. Nereson et al.

(1998) analyzed the layer shapes with the use of a numerical ow model. The modeling was complicated by the fact that accumulation gradients are likely to exist across the divide even if drifting has not resulted in a local low in bn . Unfortunately, the true accumulation pattern is not known so these gradients had to be free parameters in the modeling.

In addition, the bump is offset to the north with increasing height above the bed (Figure 5.13), suggesting migration of the divide. The divide migration rate thus becomes another free parameter.

With this many free parameters it was possible to model the bump rather well, but the relative contributions of a decrease in e and drifting could not be evaluated. It seems likely that both are involved. The estimated migration rate, based on the modeling, is 0.

3 0.2 m a 1 over the past several thousand years. In another example, Morse et al.

(1998) found that beneath the divide on Taylor Dome, Antarctica, shallower layers thickened southward while deeper layers thickened northward. Isotopic and chemical variations in a core were used to establish an age/depth time scale; it turned out that the northward-thickening layers were deposited during the Late Glacial Maximum (LGM). By using a numerical model of ice ow, they also found that the accumulation rate was much lower during the LGM.

The change in thickness gradient in the radar layering was then attributed to a change in storm tracks during the LGM, with storms coming from the north rather than from the south as at present. Such studies are important in trying to unravel the climatic changes that resulted in the ice ages..

GS1 Standards Knowledge Centre Effect of drifting snow on the velocity eld Glaciers ow over irregular b none for none eds, and thus have undulating surface pro les. Furthermore, their transverse ow patterns may be in uenced by nunataks or irregular valley walls. Patterns of both accumulation and ablation thus can be uneven owing to drifting and to shading from the.

Effect of drifting snow on the velocity eld A B Flow June snow depth (exaggerated). Figure 5.14. Effect of drifti none for none ng snow on the surface pro le of a glacier.

Owing to the additional accumulation in the lee of the surface convexity at A, ws does not need to be as high at B as otherwise would be the case.. 50 m. sun during the melt season. W none none e have just discussed one example of this from Siple Dome. Let us now consider some other examples.

To understand how drifting in uences the ow eld and surface pro le, consider the hypothetical situation shown in Figure 5.14 in which a glacier ows over a convexity in the bed, resulting in a similar convexity in the surface. Owing to drifting in the lee of the surface convexity, the normal June snow depth at B is, say, 2 m, while that at A it is only 1 m.

During a normal melt year, suppose that at A all of the snow and 0.5 m of the underlying ice melts, whereas at B, melting removes only the snow cover. Thus, the emergence velocity at A must be 0.

5 m a 1 , whereas at B it is 0. In the absence of the extra accumulation at B, the glacier would probably be thinner here as shown schematically by the dotted line in Figure 5.14.

The greater surface slope between A and C would then provide the increased longitudinal compression needed to develop a positive emergence velocity at B. The situation shown in Figure 5.14 occurs on a large scale on the surface of the Antarctic ice sheet above the western edge of Lake Vostok, a subglacial lake under 4 km of ice in central East Antarctica (see Figure 6.

13). The increase and then decrease in surface slope re ects ow of ice over a steep slope down into the lake and then an abrupt decrease in basal drag as the ice moves out over the lake. As this is an accumulation area, the thicker accumulation (as at B) is advected downglacier and buried.

Because ow rates are relatively low, ice moving over the lake experiences this excess accumulation for about 30 000 years. The excess shows up in radio echo pro les as an increase in the vertical distance between re ectors, and in an ice core from a borehole on the east side of the lake as a zone of high accumulation rate between 800 and 1100 m depth (Leonard et al., 2003).

Thule Baf n moraines (Figure 5.15), rst studied in detail by Goldthwait (1951), provide another geomorphologically signi cant.
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