Join Dr. Alley and his team as they take you on "virtual tours" of National Parks and other locations that illustrate some of the key ideas and concepts being covered in Unit 7.
Click on the first thumbnail below to begin the slideshow. To proceed to the next image, move the mouse over the picture until the "next" and "previous" buttons appear ON the image or simply use the arrow keys. Virtual Field Trip #1: Yosemite National Park
Tracking the Great Glaciers from Yosemite to Greenland and Alaska. Yosemite truly is an incomparable valley. Bridalveil Falls, on the right, is a hanging valley; its small glacier did not cut downward as rapidly as the main glacier. All photos by R. Alley
Closer view of Bridalveil Falls, right. The U-shape of the valley of Bridalveil Creek shows that it was glaciated.
Bridalveil Falls, Yosemite National Park. Bridalveil Creek has just started to cut a notch into the U-shaped cross section of the former glacial valley. The rapids at the bottom of the waterfall is running on rocks dumped there by the creek; eventually, the waterfall will be completely transformed into a rapids unless another ice age brings glaciers to re-form the waterfall.
Lower Yosemite Falls, Yosemite National Park. The numerous waterfalls of the park exist because the ice-age glaciers eroded the tremendous cliffs of the valley.
Half Dome above Yosemite Valley. A glacier flowing to the lower right deepened and widened the valley; see the next slide for a modern example.
Glacier draining Greenland Ice Sheet into head of Scoresby Sund, NE Greenland National Park. The scale is similar to that in the previous picture. Yosemite’s glaciers ended on land; this one calves icebergs into the fjord.
Near ice-sheet edge, NE Greenland National Park. The folds show that ice flows. Blue at top is a meltwater lake; such lakes may drain to the bed.
Corridoren Glacier, Greenland. The stripes are medial moraines, rock debris picked up from ridges where two tributary glaciers join.
Several tributary glaciers joining; flow is to right. NE Greenland National Park. Accumulation area in cirque (red arrow), lakes in ablation zone (green arrow) and medial moraine (blue arrow) are visible.
Accumulation zone in cirques (top), ablation zone (bottom), 150-year-old moraine (red), subtle, 11,500-year-old moraines (blue), NE Greenland Natl. Park.
Debris-bearing basal ice (red arrow) of a glacier in south Greenland. Rocks in such ice sandpaper, or abrade, the bedrock beneath as the ice moves.
The granite behind George the marmot has been abraded by debris-bearing glaciers, in the highlands of Yosemite National Park.
Rock ptarmigan on glacially striated granite (striae are faint lines on rock; a few of many are shown by blue arrows), east Greenland.
Glacially striated and polished bedrock, east Greenland. Ice flowed up the cliff from the lower right.
Glacially abraded and plucked rock in fjord wall, S. Greenland. The ice came from the left, as indicated by the arrow, scratching/abrading (S) some places and plucking (P) others. Picture is about 10 feet across.
Small snow avalanches into a cirque, east Greenland. The layered rocks are flood basalts from opening of the Atlantic Ocean.
Horn, Stauning Alps, NE Greenland National Park. Several cirques have intersected to leave this towering peak.
U-shaped valley from glacial erosion, Tracy Arm Wilderness Area, Alaska.
Moraines around retreating glaciers, Alpe Fjord, NE Greenland Natl. Park.
Moraines around retreating glaciers, NE Greenland Natl. Park.
Deposits of Bjornbo Glacier, NE Greenland Natl. Park. Ice was here about 1850. Glaciers carry pieces of different sizes, which make till when deposited.
Virtual Field Trip #2: Glacier, Glaciers and Glaciation: The Ice Really Was Bigger, Glacier National Park
Bear Grass (really a lily, not a grass) blooming in a glacier-carved but now glacier-free cirque along Going-to-the-Sun Road, Glacier National Park, Montana. All photos by R. Alley, except for some of the Alaska pictures, which are by either R. Alley, C. Alley, J. Alley or K. Alley, and we’re not sure on some of them because we kept trading cameras.
Glacier-carved scenery, Logan Pass, Glacier National Park.
Cameron Falls, Waterton Lakes, Alberta, Canada (Glacier-Waterton Lakes International Peace Park). The rocks were folded by mountain-building, and the waterfall follows the bent layers.
Female bighorn sheep, Glacier National Park. In search of salt, she was going from car to car, licking steering wheels where perspiring hands had left deposits.
Bighorn sheep. This ram was over the border in Canada, but surely has relations in Glacier.
Mountain goats are aptly named. Glacier National Park.
Glacially carved “paternoster” lakes, Glacier National Park.
Glacially truncated cliff. The ridge on the left was cut off by a glacier that reached at least as high as the sunlit peak, and that flowed over the point where the photographer stands. Glacier National Park.
Meltwater stream entering lake, surface of the Greenland Ice Sheet. At higher elevation, the ice-sheet surface is just snow. Such ice sheets now cover 1/10 of the Earth’s land, but during the last ice age covered almost 3 times more.
Caribou on the surface of the Greenland ice sheet, here about 1 mile from the edge, avoiding mosquitoes. Healed crevasses are evident. This is in the ablation zone, and meltwater plus wind-blown dust have dulled the white snow.
Bald eagle (arrow) on top of Margerie Glacier, Glacier Bay National Park, Alaska. Glaciers can be large. Glacier ice is blue, as seen here, for the same reasons that water is blue (preferential absorption of red by water molecules).
Bald eagle, Sitka, Alaska, near Glacier Bay National Park, in case you wanted to know what the bald eagle in the previous picture looks like. Mostly, this is an excuse to stick in a cool picture.
Iceberg behind float-plane propeller, Northwest Fjord, east Greenland. The berg reaches about 400 feet above the water, and is close to one-half-mile long.
Harbor seal on very small iceberg, Glacier Bay National Park, Alaska. Glaciers lose mass either by melting, or by calving icebergs.
Rainbow above iceberg, Scoresby Sound, NE Greenland National Park. Icebergs are highly relevant to the study of glaciers and ice ages, but we’re not above sticking in pictures primarily because they’re pretty.
Fulmar in front of sea ice, NE Greenland National Park. Sea ice is frozen ocean water, usually less than 10-20 feet thick. Icebergs calve from glaciers formed from snowfall, and can be more than 1000 feet thick and the size of small states.
Marble Island, in Glacier Bay National Park, Alaska, was scoured smooth by glaciers, and is now home to numerous sea lions.
An immature bald eagle (arrowed) concerns the gulls and ravens of South Marble Island, a glacially scoured rock in Glacier Bay National Park, Alaska.
The deep, glacially carved fjords of Glacier Bay National Park and surrounding Alaska are home to humpback whales and other charismatic macrofauna (big, cute critters).
Raised beaches form a bulls-eye on this small island in east Greenland. Melting of ice sheets raised global sea level at the end of the ice age, but some regions that had been depressed under the former ice sheets rebounded faster than the sea rose, raising beaches out of the water.
Satellite image of Chesapeake Bay. Geological study of the Bay and its surroundings confirms what you can see by inspection: the bay is a drowned river valley, indicating either that sea-level rose or the land fell fairly recently (mud is filling the bay; if the change happened a long time ago, the bay would be filled). Similar features along many coasts, including those being raised tectonically, show that sea level rose rather than the land falling.
Virtual Field Trip #3: Bear Meadows
What do Rocky Mountain, Bear Meadows, and Greenland have in common? Hint: It’s cold up there on top of Rocky Mountain… All photos by R. Alley, maps from USGS and NOAA.
First, some Rocky Mountain wildflowers. left: Spotted coral-root orchid, middle: Glacier lily, right: Blue columbine.
http://www.ncdc.noaa.gov/paleo/slides/slideset/11/11_177_slide.html National Geophysical Data Center, NOAA, Mark McCaffrey The last ice age was most intense between about 24,000 and 18,000 years ago. This image re-creates the northern hemisphere about 18,000 years ago (left) and today (right). Notice that broad areas now submerged were exposed during the ice age by the lower sea level (e.g., green areas west of Alaska), and that both land ice (white) and summer sea ice (gray) were more extensive then. Southern-hemisphere changes were smaller. Also notice that the ice came close to Pennsylvania.
http://www-atlas.usgs.gov/articles/geology/features/glaciallimit.html This map from the USGS uses distinct colors for different geological units. The white line shows how far south ice-age ice came from Canada. The “Driftless Area” in Wisconsin (white outlines and arrow) was missed by ice, which was channeled south along Lake Michigan and west along Lake Superior. Numerous flooded river valleys including the Chesapeake Bay (yellow arrow) are evident. Bear Meadows (pink arrow) and surroundings were beyond the Canadian ice, but must have been very cold when ice was close.
Bear Meadows, above State College, PA, occurs where natural wetlands are rare. Sediment cores indicate that the bog formed during the ice age.
Permafrost enhances mass movement (downhill creep). Direct measurements have documented motion of roughly 1 inch per year. Such downhill motion can move a lot of rocks over time, and might dam a stream occasionally. Shown here is a permafrost hillside roughly 1/2 mile across, in east Greenland, with rocks creeping downhill toward you.
This band of large blocks has moved down to just above Bear Meadows from the ridgetop, most of a mile away. (Is it any wonder that Pennsylvania hikers need good boots to avoid twisted ankles?) Trees growing on some of the rocks show that motion is not occurring now.
Permafrost often sorts stones by size, making fascinating patterns, as here in Greenland. Dr. Alley’s boot toe (bottom center) for scale.
Unfortunately, the best sorted stone circles in central PA are now obscured by leaves. Weak examples are shown here, with coarse clasts circling the finer centers, which are marked by the white “X” symbols in the lower left and right.
The tendency for moving hillsides in permafrost to align clasts tipped on edge can be seen in Greenland (right), and is evident above Bear Meadows (left).
Similarities in size and orientation of blocks in flows that have moved downhill are evident in Greenland (right) and above Bear Meadows (left).
Present and Past Permafrost Hillsides.
Virtual Field Trip #4: Are Glaciers Really Changing?
Are glaciers changing? Yes. Over the last century, and over the last few decades, the great majority of glaciers on the planet have gotten smaller. Over shorter times, the “fun things” glaciers do (surges, kinematic waves, etc.) have caused some to grow while others shrank, but overall shrinkage is strong. Here are some photo pairs, historical and more recent, assembled by Bruce Molnia of the United States Geological Survey, and archived at the National Snow and Ice Data Center. The lenses used are not always identical, but the photos are taken as nearly as possible from the same spot, and you should be able to see the changes clearly.
Muir Glacier, Alaska, August 13, 1941, photo by B.F. Molnia.
Muir Glacier, Alaska, August 31, 2004, photo by W.O. Field.
Holgate Glacier, AK, July 24, 1909, photo by U.S. Grant.
Holgate Glacier, AK, Aug. 13, 2004, photo by B.F. Molnia.
McCarty Glacier, AK, July 30, 1909, photo by U.S. Grant.
McCarty Glacier, AK, Aug. 11, 2004, photo by B.F. Molnia.
McCarty Glacier, AK, Aug. ??, 1906, photo by C.W. Wright.
McCarty Glacier, AK, June 21, 2004, photo by B.F. Molnia.