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 9.
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: Bryce Canyon National Park
BRYCE CANYON: “A Hell of a Place to Lose a Cow”--Ebeneezer Bryce
Although Bryce Canyon is higher, cooler, and wetter than many of the nearby parks, life is still tough on the unstable slopes of the canyon. Here, 2-inch-tall dwarf columbine (right) and a dewy Oregon-grape leaf struggle to grow at Bryce.
Cedar Breaks National Monument, near Bryce, has the same sort of limestones as Bryce, of the same age. Notice where a small fault has offset the white layer in the upper-right corner (yellow arrow).
As at Arches, water works wonders widening joints. But the rocks here are not strong enough to hold up arches, instead making hoodoos (towers usually with harder rocks on top).
Much of the coloration is linked to how rusty the iron is in the rocks. The sedimentary layering is quite evident.
Guidebooks almost always refer to Bryce as a hoodoos close up.
The Park Service now discourages “naming” rocks, because visitors are so disappointed when erosion then changes those rocks. This one was named Queen Victoria back when naming was condoned. The layered sedimentary rocks are beautiful by any name.
Trees in Bryce Canyon, with CAUSE students Sameer Safaya (far right) and Sam Ascah.
A decade or so ago, the Park Service put the logs (yellow arrow) across the stream bed to slow the burial of a trail by sediment. As we’ve seen with dams, rocks filled the space upstream from the logs, and erosion happened downstream. Fast erosion supplied lots of rocks to fill the “lake” above the dam quickly.
Bryce’s rocks are mostly limestones, but include river gravels such as the conglomerate shown here. Many types of clasts are present; the orange one in the middle is a conglomerate itself, and the clasts in it include several types of sedimentary rocks. This picture shows a long and complex story--try telling it.
Virtual Fieldtrip #2: Arches National Park
ARCHES NATIONAL PARK: Stories in Stone Photos by R. Alley
Dr. Anandakrishnan, Arches National Park. The La Sal Mountains in the background are named for the salt beneath them. The motion of the salt created joints that then isolated the fins that made the arches, such as the one next to Dr. Anandakrishnan’s shoulder.
This isn’t Arches, but Utah’s new Grand Staircase-Escalante National Monument. Plants follow water that soaks down into joints in the fossil dunes of the Navajo Sandstone, making the grid pattern in the rocks. Various joint patterns exist; parallel rather than crossing joints are very important in making arches at Arches, as we will see next.
End-on (top) and angled (bottom) views of fins, Devils Garden, Arches National Park. The tough sandstone has been broken by parallel, vertical joints, and weathering along those joints isolates “fins” of sandstone that then are eroded to make arches.
The sandstone of Delicate Arch started as a sand dune (note bedding, top-right picture).
CAUSE student Raya Guruswami in Glen Canyon (right), and a cliff in Canyon de Chelly National Monument (top). Rockfalls from the sandstone cliffs have left arch-shaped amphitheaters. Similar falls from fins help make arches.
(right) The arrow points back up from the fallen rock to its arch-shaped scar. (left) Fallen rocks are gone, but the black arrow shows their arch-shaped scar. Two views of fossil sand dunes over redder flood-plain muds, Grand Canyon. Sand fills a gigantic mud crack on the right (yellow arrow). Today, sand dunes encroach on the Nile in a very similar setting. The arch-shaped rockfall scars suggest how arches may form.
CAUSE instructor Eric Spielvogel photographing a lupine near Double Arch. The high desert of Arches is a harsh environment, but surprisingly beautiful flowers appear after the rare, brief rains.
Double Arch. The dark streaks down the rock are desert varnish, mineral deposits formed partly by microorganisms that grow briefly when rainwater runs down the rock.
Desert varnish at Double Arch. The arrow points along a crack through which rainwater flows to form desert varnish. Enlargement of the crack will eventually lead to rockfall, changing the arch.
CAUSE student Dave Witmer (above) and instructor Eric Spielvogel (right), Double Arch. Rockfalls have helped shape the immense cliffs.
Mud deposited in a small lake near the sand dunes dried and cracked in the sun. More mud washed in and filled the cracks. After the mud hardened, the rocks were split apart, and the upper piece turned over; Dr. Alley’s index finger points to the crack-filling mud.