Glacial Erosion

Glacial valleys and fjords are among the most spectacular examples of combined erosion by glacier ice and meltwater. Such valleys may be 100s to >1000 m deep and extend for 10s to >100 km in length. They are typically found in mountains or rugged upland areas that were invaded by ice sheets or subjected to local valley glaciation and are

FIGURE 12-1 Triad of effects created by glaciation, on which modern glacial geomorphology is based. Taken from Aber and Ber (2007, fig. 1-5).

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FIGURE 12-2 Conventional, panchromatic airphoto of the Crestwynd vicinity, southern Saskatchewan, Canada. Large ice-shoved ridges cross the scene from NW to SE. Photograph A21639-7 (1970); original photo scale = 1:80,000. Reprocessed from the collection of the National Air Photo Library, Natural Resources Canada. Taken from Aber and Ber (2007, fig. 2-20).

FIGURE 12-2 Conventional, panchromatic airphoto of the Crestwynd vicinity, southern Saskatchewan, Canada. Large ice-shoved ridges cross the scene from NW to SE. Photograph A21639-7 (1970); original photo scale = 1:80,000. Reprocessed from the collection of the National Air Photo Library, Natural Resources Canada. Taken from Aber and Ber (2007, fig. 2-20).

FIGURE 12-3 Palisades State Park in eastern South Dakota, United States. Glacial meltwater eroded a spillway channel across a bedrock ridge composed of hard quartzite. The vertical wall of the spillway can be seen on the right side of this oblique view toward the southwest. Kite aerial photo by JSA, July 1998.

FIGURE 12-3 Palisades State Park in eastern South Dakota, United States. Glacial meltwater eroded a spillway channel across a bedrock ridge composed of hard quartzite. The vertical wall of the spillway can be seen on the right side of this oblique view toward the southwest. Kite aerial photo by JSA, July 1998.

especially common where montane glaciers descended into the sea or large lakes. Famous examples include Hardangerfjord, Norway; Konigssee, Germany (Fig. 12-4); and Lake Okanagan, British Columbia, Canada.

The Finger Lakes occupy a series of long, straight valleys that penetrate the Appalachian Plateau south of the Lake Ontario lowland in west-central New York, United States (Fig. 12-5). The Finger Lakes are often described as inland fjords because of their deeply eroded bedrock valleys and thick sediment infill. The valleys are generally wide and shallow toward the north with thin sediment fill, and the troughs become narrow, deep gorges to the south with thick sediment fill. The Finger Lakes troughs were eroded by strong ice-stream flow coming from the north enhanced by high-pressure subglacial meltwater drainage (Mullins and Hinchey, 1989).

Among the individual Finger Lakes, Keuka Lake is the most unusual because of its branched shape (Fig. 12-6). SFAP was conducted with a small helium blimp at Branchport at the northern end of the west branch of the lake. Most of the surrounding land is heavily forested or agricultural (Fig. 12-7), which limited ground access for SFAP, so an open field at a school was utilized as the spot to

FIGURE 12-4 Königssee, a lake in a deep ice-carved valley on the northern side of the Alps, Berchtesgaden National Park, southern Germany. Ground photo by JSA, July 2007.

FIGURE 12-5 Astronaut photograph taken from the space shuttle over the Finger Lakes district of western New York. Asterisk indicates Keuka Lake. STS 51B-33-028, April 1985. Hasselblad, 70-mm film, near-vertical view. Courtesy K. Lulla, NASA Johnson Space Center.

FIGURE 12-6 Topographic map of Keuka Lake vicinity in west-central New York. Length of Keuka Lake from Penn Yan to Hammondsport is ~32km; elevations in feet; contour interval = 50 feet (~15 m). Asterisk indicates SFAP ground site. Adapted from Elmira NK 18-4, New York, 1:250,000 (1973), U.S. Geological Survey.

FIGURE 12-5 Astronaut photograph taken from the space shuttle over the Finger Lakes district of western New York. Asterisk indicates Keuka Lake. STS 51B-33-028, April 1985. Hasselblad, 70-mm film, near-vertical view. Courtesy K. Lulla, NASA Johnson Space Center.

launch the blimp. Oblique photographs were acquired with a primary focus on the valley of Sugar Creek to the north and West Branch Keuka Lake to the south (Fig. 12-8). These views emphasize the long, straight nature of the valley bounded by steep bluffs incised into the upland plateau.

The Tatra Mountains in southernmost Poland and northern Slovakia are part of the Carpathian Mountain system of east-central Europe. The Tatras experienced significant tectonic uplift within the past few million years, and highest peaks exceed 2500 m elevation. The Tatras supported numerous alpine glaciers during the Pleistocene, and these glaciers left behind a classic assemblage of

FIGURE 12-6 Topographic map of Keuka Lake vicinity in west-central New York. Length of Keuka Lake from Penn Yan to Hammondsport is ~32km; elevations in feet; contour interval = 50 feet (~15 m). Asterisk indicates SFAP ground site. Adapted from Elmira NK 18-4, New York, 1:250,000 (1973), U.S. Geological Survey.

ice-carved valleys, moraines, and outwash deposits. The combination of tectonic uplift and glaciation led to rapid erosion, and extensive alluvial fans were deposited from streams and glacial meltwater along the southern flank of the range.

Kite aerial photography (KAP) was conducted on both sides of the Tatra Mountains in order to document and understand better the geomorphic features connected with glaciation (Aber et al., 2008). On the southern flank, broad alluvial fans form a conspicuous apron that slopes southward from the Tatra range into lowlands (Fig. 12-9). Much of the surficial sediment was derived from deep glacial erosion of valleys within the mountains. Among the largest of these valleys is Vel'ka Studena dolina, which is some 6 km long and more than 1000 m deep (Fig. 12-10).

The appearance of the Tatra Mountains on the Polish side differs considerably. The mountain front ends abruptly along a linear trend adjacent to a relatively low flanking valley without prominent alluvial fans to mark the transition (Fig. 12-11). Within the Polish Tatras, glaciated valleys are abundant (Fig. 12-12), but generally are not so long nor so deep as on the Slovak side. Kite aerial

FIGURE 12-7 Panoramic ground view of KeukaLake looking toward the northeast from the western side. The lake is about 1.2 km wide to right (south) and branches into two major arms toward left. Note heavily forested terrain. Adapted from Aber and Ber (2007, fig. 9-11).

FIGURE 12-8 Oblique views of glaciated valley at Branchport, New York, United States. (A) View over West Branch Keuka Lake looking south toward the sun. (B) View northward along the valley of Sugar Creek (visible in lower right corner). The upland plateau in right background stands ~90 m above the valley floor in foreground. Helium-blimp aerial photos by JSA and SWA, August 2005.

FIGURE 12-8 Oblique views of glaciated valley at Branchport, New York, United States. (A) View over West Branch Keuka Lake looking south toward the sun. (B) View northward along the valley of Sugar Creek (visible in lower right corner). The upland plateau in right background stands ~90 m above the valley floor in foreground. Helium-blimp aerial photos by JSA and SWA, August 2005.

FIGURE 12-9 Wide-angle view of the southern Tatra Mountains looking toward the northwest from near Stara Lesna, Slovakia. The broad terraces in the foreground and left background represent alluvial fans built of gravelly sediment washed out of the Tatra Mountains, in part by glacial meltwater. Kite aerial photo by JSA and SWA, July 2007.

FIGURE 12-9 Wide-angle view of the southern Tatra Mountains looking toward the northwest from near Stara Lesna, Slovakia. The broad terraces in the foreground and left background represent alluvial fans built of gravelly sediment washed out of the Tatra Mountains, in part by glacial meltwater. Kite aerial photo by JSA and SWA, July 2007.

photographs emphasize the geomorphic differences between the northern and southern sides of the Tatra Mountains, a situation not readily obvious from conventional maps or satellite images.

In the general scheme of alpine glaciation in the northern hemisphere, glaciers on northern sides tend to be larger and, thus, have more geomorphic impact than glaciers on southern sides of mountain ranges. But this is not the case in the Tatra Mountains, as demonstrated by SFAP, where recent tectonic uplift and fault movements have played important roles for glaciation and landform development.

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