Page 583 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 17 glacial and Periglacial Landscapes 547
Fjord
N
HPS 19
Penguin Glacier
Fjord
▲Figure 17.13 Fjords on the Pacific Ocean side of the Southern Patagonia Ice Field, Chile. as ice from the Penguin glacier and HPS 19 flows into fjords, it calves and forms ice- bergs. (HPS stands for Hielo Patagónico Sur, or Southern Patagonia ice Field, in the number- ing system for glaciers with no geographic name.) The largest iceberg in the image is about 2 km in width. [naSa ISS astronaut Photo.]
CRITICALthinking 17.1 Looking for Glacial Features
after looking at Figure 17.12 to identify glacial features, go back to the photos in the chapter opener and Figures 17.1 and 17.3, and then examine Figure 17.12 again. List all the glacial formations that you can identify in these photos. are there any erosional landforms you find on all the pho- tos other than the glaciers themselves? •
Depositional Landforms
Glaciers transport materials upon and within the ice, producing unsorted sediment deposits, as well as by the actions of meltwater streams at the glacier’s downstream end, producing sorted deposits. The general term for all glacial deposits, both unsorted and sorted, is glacial drift.
Moraines As mentioned earlier, as a glacier flows to a lower elevation, a wide assortment of rock fragments be- come entrained (carried along) on its surface or embedded within its mass or in its base. As the glacier melts, this un- sorted and unstratified debris is deposited on the ground as till, usually marking the glacier’s former margins.
The deposition of glacial sediment also produces a class of landform called a moraine, which may take sev- eral forms. In areas that have undergone alpine glacia- tions, lateral moraines are lengthy ridges of till along each side of a glacier. If two glaciers with lateral moraines join, a medial moraine may form (see Figure 17.1). In areas that
were formerly covered by single, large ice sheets, lateral moraines and medial moraines are lacking.
End moraines accumulate at the glacier’s termi- nus, or endpoint, and are associated with both alpine and continental-scale glaciation. Eroded debris that is dropped at the glacier’s farthest extent is a terminal moraine (Figure 17.15). Recessional moraines may also be present, having formed at other points where a gla- cier paused after reaching a new equilibrium between accumulation and ablation.
Till Plains When the ice sheets retreated from their maxi- mum extent, about 18000 years ago, during the most
▲Figure 17.14 Norwegian fjord. Sediment carried in runoff is visible in this fjord, which fills a U-shaped, glacially carved valley. [Bobbé Christopherson.]