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 10.
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 Fieldtrip #1: Great Basin National Park and the Lehman Caves
Great Basin National Park’s Wheeler Peak, Nevada--Caves, Bristlecones, and the Age of the Earth Diagram from NOAA, photos from National Park Service (indicated) and by R. Alley
Cave formations, Lehman Cave, Great Basin National Park “Popcorn” on column (left), helectites on column (center) and flowstone (right).
http://www.nature.nps.gov/geology/caves/gallery/speleothems/shield.htm and bifrost_soda_straws.htm A shield (left) and hollow stalactites (soda straws; right). The National Park Service Web site doesn’t identify the cave pictured, but because shields are almost unique to Lehman Caves, and twisty stalactites (called helectites) are common there as well, these images are probably from Lehman.
Bristlecone pines live fast and die young in “good” environments (wet and warm, with rich soils), but live long if barely prospering in cold, dry environments with impoverished soils. These are at Cedar Breaks National Monument, Utah.
The distinctive “bottle-brush” branches of the bristlecone pines (left, at Cedar Breaks) look like they are ready to clean test tubes in a lab. The rapid erosion at Bryce (right) leaves bristlecone roots exposed above the ground.
Still more bristlecones, this time on Mt. Evans, Colorado. The tree shown at right is kept alive by a narrow strip of bark (yellow arrow), while most of the tree has had its bark sand-blasted away or otherwise removed (pink dashes). Tree-ring dating must be done under the living strip of bark.
http://www.ncdc.noaa.gov/paleo/slides/slideset/index18.htm Laboratory of Tree-Ring Research, The University of Arizona, NOAA Paleoclimatology Program Slide Set on Dendrochronology. In this example of cross-dating in tree-ring research, the pattern of thick and thin rings in a core from a living tree (A) is matched to the pattern in a dead tree (B), then to wood in a native-American site, C, and then on to other, older wood samples (D-J).
Long House, Mesa Verde National Park. Construction was done mostly with stone and mud, but also with some wood (log in upper right, arrow), often hauled in from long distances. Tree-ring studies allow reconstruction of ages and of past climates.
Museum specimen (upper right), and logs from Long House (above and right; arrow on right shows plug removed for tree-ring research and replaced by modern wood), Mesa Verde.
Virtual Fieldtrip #2: Grand Canyon National Park
Grand Canyon National Park
http://asterweb.jpl.nasa.gov/gallery-detail.asp? data-cke-saved-name=PGC name=PGC NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team Satellite-generated oblique view of the Grand Canyon, looking across the South Rim Village (lower right, yellow label “S”) toward North Rim Village (“N”).
http://landsat.usgs.gov/gallery/detail/371/ USGS Landsat image. At 277 miles long, 5 to 18 miles wide (average 10 miles wide), and about 5700 feet deep (just over a mile), Grand Canyon is not the longest, deepest, widest, or steepest on Earth, but it may be the grandest for combining length, depth, width, and steepness. South Rim Village (S) and North Rim Village (N) are indicated.
http://data2.itc.nps.gov/hafe/hfc/npsphoto4h.cfm?Catalog_No=hpc%2D001583 National Park Service Historical Photo, helicopter-rescue training exercise. National Park Service web site says: “Over 250 people are rescued from the Canyon each year. The difference between a great adventure in Grand Canyon and a trip to the hospital (or worse) is up to YOU - follow the rules of smart hiking and - DO NOT attempt to hike from the rim to the river and back in one day, especially during the months of May to September.”
Some who didn’t need help hiking to the bottom of the canyon and back. (left) Left to right, CAUSE students Stephanie Shepherd, Dave Witmer, Sameer Safaya, Sam Ascah and Irene McKenna, at Silver Bridge after moonlight hike to the bottom of the Canyon. (top right) Geography staff member Anna Brendle and videographer Topher Yorks (bottom right) Raya Guruswami and Sam Ascah
Mule deer in feeding trough for pack mules, and Columbian ground squirrel, Indian Gardens, Grand Canyon.
(left) California condors have been reintroduced to the Canyon successfully (right). It is a pleasure to see them wheeling above the vast spaces.
Despite the dryness, the Canyon has many beautiful flowers. Prickly pear (upper left), phlox (left), century plant (center), and penstemon (right).
South Bright Angel Trail (left), and having a little fun with it (right).
Metamorphosed rocks abraded and polished by Colorado River, Bright Angel Trail. Note that river-worn rocks look very different from glacier-worn rocks, but show clear evidence of erosion.
Sunset at the Canyon. It is worth the trip…
Virtual Fieldtrip #3: A Geologic Walk Out of the Grand Canyon—Climbing Time
A Geologic Walk Out of the Grand Canyon—Climbing Time. All pictures from USGS (as indicated) or by R. Alley
Rock units of the Grand Canyon, as seen from the south rim on the Bright Angel Trail. Temple Butte is discontinuous (as is the Surprise Canyon, a recently discovered unit just above the Redwall). The Supai Group and the Grand Canyon Supergroup include several named layers.
Above Bright Angel campground (just N. of the Colorado River up Bright Angel Creek near the bottom of the Canyon). Here, sedimentary rocks of the Precambrian Grand Canyon Supergroup rest on the unconformity (yellow line) above metamorphosed rocks.
Views of the N. side of the Colorado River from Bright Angel Trail, showing Zoroaster granite (pink) intruded into Vishnu Schist (dark) and heavily deformed, from the heart of an old mountain range.
Push-together fault (yellow) offsets and bends Precambrian metamorphic rocks (below the blue lines) and Grand Canyon Supergroup sedimentary rocks (above the blue). This fault was active before younger deposition (Paleozoic Tapeats Sandstone, above the pink line).
http://libraryphoto.cr.usgs.gov/htmllib/parks1.htm, USGS med00280, photo 434 The “Great Unconformity” between Precambrian Grand Canyon Supergroup (below yellow lines) and Cambrian Tapeats Sandstone (above the yellow). The total thickness of the lower rocks is about two miles--from upper right, measure rock thickness down pink line, walk along layer on blue line, go down pink line, along on blue…and repeat out of the picture to the left.
Precambrian rocks (below the Great Unconformity, marked in yellow) and Paleozoic rocks (above the yellow line), east end of Grand Canyon National Park.
Sedimentary layers in the Tapeats Sandstone. Cross-bedding (right) and ripple marks (seen edge-on above, yellow arrow) are among features shown. These are “normal” sediments, lacking signs of catastrophic or sudden deposition.
Burrows (yellow arrows) in Tapeats Sandstone (left) and Supai Formation (right). Creatures hide in mud or crawl through mud looking for food, leaving tracks. Time clearly is required for this to happen. Burrows occur throughout the upper mile or so of the Canyon’s rocks.
Mud cracks also are found in many, many layers of the Canyon, from many times when the sediment surface was stable long enough for cracks to form. Those to the right are in a block that fell from the Kaibab Limestone cliff, and those on the left are in the Bright Angel Shale, along the South Bright Angel Trail.
Both photos from USGS. (left) Shelly limestone from channel fill in basal Supai rocks, with trilobite tail (upper left) and some beautiful gastropods (snails). (right) Algal-mat (stromatolite) deposits, Chuar Group, Precambrian Grand Canyon Supergroup. Mats trapped mud, grew up through the mud, and trapped more.
100-foot-high cliff of Hermit Shale (below yellow line) and Coconino Sandstone (above, and shown in one-foot-wide close-up in upper left to reveal the fossil-sand-dune nature of the Coconino). Below the pink arrow, the Coconino sand fills a mud crack in the Hermit Shale. South Bright Angel Trail, Grand Canyon.
http://libraryphoto.cr.usgs.gov/htmllib/parks1.htm, USGS med00324, photo 460 (above) and 372ct, photo 476 (right). Fossil trackways, from the Supai Formation (above; foot was about 4 inches across) and the Coconino Sandstone (right). Diverse fossil tracks have been found at many different levels in the Canyon.
http://libraryphoto.cr.usgs.gov/htmllib/parks1.htm USGS med00121, photo 393 (left; photo from National Park Service) and medb0125, photo 394 (right). Two sets of trackways in the Coconino Sandstone. On the left, a reptile walked up a sand dune. On the right, millipedes were among those leaving their marks (blue arrow and similar tracks).
http://libraryphoto.cr.usgs.gov/htmllib/parks1.htm USGS nlf00128, photo 505 Still more fossil trackways from the Coconino fossil sand dunes in the Grand Canyon. Left: Lizard trackway, National Park Service museum, South Rim. Right: Historical photo taken about 1920 of sample from Hermit Trail.
Trilobite (upper right), Bright Angel Shale. USGS Brachiopod (upper left) and fossil-bearing limestone (lower left) along South Bright Angel Trail, plus nautiloid now in Grand Canyon Museum, all from Kaibab Limestone. Photos by R. Alley.
The history of the Canyon did not end with the deposition of the Kaibab Limestone, which slants down to the north beneath Zion, and Zion’s rocks slant beneath Bryce… After the deposition, erosion of the Canyon has occurred (see the Enrichment in the text), and deformation has happened. Here, the South Bright Angel Trail crosses the Bright Angel Fault--the blue arrow points at the pulverized rocks of the nearly vertical fault zone.
Word Document of Unit 10 V-trips