In and About Tuff Canyon, Part 8: A Tale of Two Fluids, Big Bend National Park, Texas, USA

Standing in the bed of the canyon-forming Blue Creek. The tree that's eking out a living in the joint in the wall is a Honey Mesquite (Prosopis glandulosa). That vertical crack must be joint rather than a fault, because there's no noticeable displacement of the layers on either side.

I could have subtitled this shot "Rocks-a-Rama," because it certainly features a lot of stones on display. They include those that were transported and dumped here by two fluids of different densities.

On the creek bed, there are those deposited by water itself. This good example of alluvium is a poorly sorted assortment of sand, gravel, cobbles, and small boulders. They all remain in a state of repose until the next flash flood comes surging through, and moves them a little closer toward the Rio Grande.

Also of great interest is the very rocky stratum near the bottom of the cliff. It's a lahar or debris flow deposit. These stones, of all shapes and sizes, were carried along by a volcanic mudflow, a porridge- to soup-like glop composed of airfall ash that mixed, one way or another, with enough lubricating water to flow down a hillside or channel. For a closer look at what this substance looks like when lithifed, see Part 7.

In populated regions, modern lahars can be tremendously destructive, and there are various gruesome examples of houses, automobiles, and even whole towns getting entombed in the mud before their occupants can escape. (If you don't believe me, just look up Colombia's 1985 Nevado del Ruiz lahar that buried the city of Armero, with a death toll of more than 20,000.)

My other photos and descriptions in this series can be found in my Canyonlands album.

Taken in: United States / Texas / Castolon (show map)

Taken on: March 14, 2002

Tags:

geology

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Texas

Tuff Canyon

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Sets appears in: • Canyonlands • Natural History: Big Bend Region & All of Trans-Pecos Texas more » • Overt Tree Worship • Rock Forms, Rock Formations « less

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Camera: MAKER NAME 96660, f/1.8, 1/41 sec, 2.8mm, ISO 50 (more info) (hide info)

Camera:	MAKER NAME 96660
Aperture:	f/1.8
Exposure Time:	0.024 sec (1/41)
Focal Length:	2.8mm
ISO:	50
Exposure Bias:	0 EV
Flash:	Auto, Did not fire
Exposure Program:	Program AE
Metering Mode:	Average
White Balance:	Auto
Color Space:	Uncalibrated
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