Tectonic geomorphology at late Cenozoic time scales - Tectonic Geomorphology - page 353

Glacial Valley Proiles Mean Elevation

37˚N 37˚N

G

steep
small glacier

4755 4755

gentle
large glacier

K

deglaciated
zone

4601 4601

3973 3973

RH

4081 4081

A: Rapid Rock Uplift

3222 3222

SN

gentle
small glacier

GS

4087 4087

gentle
large glacier

deglaciated
zone

3774 3774

NP DD

D

4290 4290

35˚N 35˚N

B: Slow Rock Uplift

Mean Snowline

37˚N 37˚N

Fig. 10.39 Glaciated topography as a function of
rock-uplift rate.
Glacial valley profiles resulting from average Quaternary
conditions: ∼ 400 m of snowline lowering. A. Glacial
valley profiles under rapid rock-uplift regimes. Both
headwall relief and the gradient of small glaciers increase,
whereas large glaciers retain their low gradients.
B. Under slow rock-uplift regimes, both large and small
glaciers have gentle gradients and headwall relief is
modest. Modified after Brocklehurst and Whipple (2007).

rapid rock uplift include significant increases in
the height of cirque headwalls, a modest rise in
mean elevation (due largely to the headwall
lengthening), and a steepening of moderate- to
small-sized glaciers (Fig. 10.39).
Even in rapid uplift zones, large glaciers
retain low gradients, suggesting that they erode
effectively irrespective of rock-uplift rate. At
least two factors could serve to enhance glacial
erosion in regions of rapid rock uplift. First,
these areas often contain very high peaks, even
if the mean elevation is not particularly high.
Such peaks have been termed “topographic
lightning rods” because of their role in causing
more precipitation on their flanks (Brozovi ´
et al ., 1997). Greater ice fluxes should lead to
more rapid erosion. Second, although one's
eyes are attracted to the high summits, only a
few percent of the total topography will
typically occupy the upper 10-20% of the range
in elevation. For example, in the Himalaya, our

35˚N 35˚N

0 50 100 km

Snowline Elevation (m)

<4600 <4800 <5000 <5200 <5400 <5600 >5600

Fig. 10.38 Mean elevations and mean snowlines in
the northwest Himalaya.
(Top) Mean elevation (meters) of subregions in the
northwest Himalaya. D: Deosai Plateau; DD: dissected
Deosai; NP: Nanga Parbat; RH: Rakaposhi-Haramosh;
SN: Skardu north; K: Karakoram; G: Ghujerab. (Bottom)
Elevation of modern snowline in the same region as
shown above. Note that snowlines also rise toward the
northwest and generally lie

∼

700-1000 m above the
mean elevations. The topographic and snowline
gradients trend at nearly right angles to the tectonic
gradients in this region (Fig. 10.28). Modified after
Brozovic´ et al . (1997).