. Elementary physical geography . alley glaciers amongmost of the mountains of Alaska (Plate 26), in BritishColumbia, in some of the high mountains of Washington,such as Mt. Shasta (Fig. 174), and in several places inthe Sierra Nevadas (Fig. 177). The glaciers of the westare small and insignificant, but those of Alaska are among the best developedin the world. Val-ley glaciers are byno means uncom-mon in other partsof the earth ; and,among otherplaces, we findthem in Norway,New Zealand, andTierra del most of the al-pine glaciers ofthe northern hem-isphere, there isevidence that inthe
. Elementary physical geography . alley glaciers amongmost of the mountains of Alaska (Plate 26), in BritishColumbia, in some of the high mountains of Washington,such as Mt. Shasta (Fig. 174), and in several places inthe Sierra Nevadas (Fig. 177). The glaciers of the westare small and insignificant, but those of Alaska are among the best developedin the world. Val-ley glaciers are byno means uncom-mon in other partsof the earth ; and,among otherplaces, we findthem in Norway,New Zealand, andTierra del most of the al-pine glaciers ofthe northern hem-isphere, there isevidence that inthe period imme-diately precedingthe present, theyextended farther down their valleys than at present. The valley glacier has its beginning in the snow field ofthe higher portions of the mountains, which are the greatfeeding grounds (Fig. 67). Here the more level portionsof the ground are permanently covered with snow, theaccumulation of many winters. As this increases in depth,it is unable to remain on the steeper portions and drops. Fig. 175. The Rhone glacier, showing the ice stream fromsnow field to terminus. GLACIERS. 309 down the hillsides into the valleys, in the form of greatsnow avalanches. Here it begins a slow movement downthe valleys, whose slopes are usually steep; and in thecourse of this movement, the snow becomes compactedinto ice, and is transformed to the true moving glacier(Fig. 175). The rate of movement is exceedingly slow,and unless watched very carefully, is not noticeable. In ameasure, its movement may be compared to that of river water,although this comparison is capable of being extended onlyin a very general way. It moves more rapidly in the centralportion than on the margins, and, like water, it graduallymoves down the grades. Ifthe valley grade is regular, thesurface of the ice is compara-tively smooth, although it mayhere and there be creased byfissures or crevasses (Fig. 176).When the valley bottom isitself very irregular, and theslope changeable, the
Size: 1862px × 1342px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthortarrralphsralphstockm, bookcentury1900, bookdecade1900
