By Assistant Chief Ranger George L. Collins
ALL Grand Canyon waterways, including not only the Colorado River, but several tributary streams as well, are characterized by their extremely unusual surroundings. They become immediate centers of interest wherever seen because they are practically the only animating features disclosed to view. There is an absorbing interest for anyone in watching the Colorado River's wild rush through its narrow channel deep down within the Grand Canyon. One cannot help but be deeply stirred in such a setting by the strange personality of power, mystery and loneliness the river manifests.
Almost, all visitors are caused to reflect on the story of relentless wearing away expressed by the Grand Canyon streams, with its many ramifications in thought of beauty and size and power. Such reflection is brought about primarily because people are able actually to see the streams at work. Observational evidence of such things always seems most impressive as is attested by the idea that although there are other streams flowing within the Grand Canyon mighty streams, in fact, covering the whole area they are nevertheless quite ignored by the average visitor simply because he cannot see them. Yet there they are; working more gently and with less concentration than the rivers of water perhaps, but as ceaselessly contributing their share in the general scheme of things. You have guessed by now that the reference is to those other great streams streams of air which twist and swirl so sleekly in and about the Canyon.
On some cool day you may have witnessed the smoke from Grand Canyon Village flowing along close to the ground and then over the Canyon rim to tumble down and down into the depths, perhaps for some hundreds of feet or more before it disperses.
This sight occurs frequently during periods of cool or cold weather when smoke hangs heavily and the prevailing wind, in flowing up from the south over gradually elevating land surfaces, becomes steadily colder and heavier until, on reaching the rim, a giant air cascade occurs just as would a waterfall. If the village chimneys are smoking in any volume at that time, the course of air in its fall will be indicated somewhat as the smoke is carried along.
Grand Canyon Airlines pilots tell us that the prevailing southwest wind averages some 800 feet in depth or thickness. At times it may be much greater, depending, of course, on temperatures and the accompanying fluctuations in density. Above it are other air currents in succession reaching up through the troposphere and tropopause to those frigid and vaporless levels of the stratosphere.
As the air stream tumbles down into the Canyon it expands swiftly due to higher temperatures encountered. (The difference from rim to bottom being about 15 degrees normally with a far broader change at times.) The action here is the same as occurs when cold air is admitted into a heated room. It settles toward the floor until lightened by warmth and expansion. Then it rises toward the ceiling. So does the stream of air we are following settle into the Grand Canyon to join with other local circulations in forming a great up-draft or vertical column which, if visible, would certainly appear as a gigantic fountain rising generally over the central portion of the Canyon.
This fountain is ceaseless in its activity since the Canyon is so deep that air at rim temperature never reaches the bottom. Quite infrequently, however, during periods of especially cold weather, it may not rise more than a short distance before being equalized and largely dispersed, by refrigeration penetrating from rim areas for a considerable distance down into the gorge.
In addition to the stream of air we have been tracing, there are many other local air currents to complete the picture. For instance, there are drafts coursing up and down the inner gorge, and also the smaller side canyons.
Apparently the air rolls and twists in a continuous side play attendant on the general trend. But in all the mysterious tumult of convection currents which one would see if air were visible, the great up-draft would no doubt be the most imposing feature. Just as a symphony is built around a central theme so does our fountain "carry the air" in the magnificent symphony of inner-canyon winds.
Sometimes there is immense force shown by this fountain of air. Aviators have passed over the Canyon edge at a thousand feet or more above ground and after entering the zone of upward flowing air found their planes steadily elevated for hundreds of feet simply through the lifting power of this current. One pilot told us that a glider could probably ride the canyon winds for days at a time with no particular struggle for elevation - perhaps sometime it may be tried.
Since the air is thus able to support such large bodies as air-crafts, it is not hard to imagine how easily it carries its mass of fine sand-particles, sometimes accompanied by rain, as cutting tools with which to grind away at canyon walls in the usual manner of wind erosion.
Aircraft not of man's design sometimes ride the Canyon air streams and by their presence disclose more evidence of interest to our story. These are masses of vapor, the stately cloud formations which sail upward in vast squadrone so quietly and beautifully after some local storms.
We find that during a storm period the air is unusually heavy laden with moisture and it is probably somewhat colder. After the air stream has tumbled down into the Canyon and expansion has taken place, it rises in the up-draft to the upper levels where refrigeration and cloud creation follow quickly; just as the hot, damp air gushes out of your tea kettle spout to vaporize almost immediately as it comes in contact with the cold air. Sometimes this action occurs far below the Canyon rims and the clouds bore upward, seemingly as ships on a vertical ocean.
Perhaps during such a period conditions will cause rain to fall from these clouds of vapor - again, just as condensation from your tea-kettle is so great at times that drops of water fall and splutter out upon the stove. Not always, by any means, but occasionally, rain will fall into the Canyon and be absorbed by the warmer and dryer air near the lowest levels to such degree that only a few drops ever reach the bottom. Inner-canyon trail parties have thus actually passed with no discomfort directly under showers of rain which have given higher reaches of the Canyon a good soaking.
Probably there is nothing so unusual about air streams of the Grand Canyon, at least to the average visitor, that any special effort need be made to point them out to him. They are, however, vastly important as an indication of those many forces of nature which are ceaselessly at work in the never-ending process of creation going on about us, not only at Grand Canyon, but wherever else we are as well.
Not long before this issue of Nature Notes went to press the writer was one morning sweeping from the parapet of Yavapai Station a few hours' accumulation of fine sand particles deposited there by the wind. Only a light breeze was blowing that morning. Through its gentle pulsing could occasionally be heard a muted bass from the Colorado River far below. Wisps of clouds, like fairy fingers light entwined, were forming in the sea of sky which fills our mighty gorge.
As I paused for a moment to absorb something of the glorious spectacle disclosed, the whine of a powerful airplane motor came into hearing. Soon the machine appeared like a lazy bumble-bee singing dolefully along its course. There was the river, the Canyon, the clouds, the wind and the airplane. At my feet was a handful of sand. How closely related they were; how closely interrelated with the forces of nature is man's mastery of his environment.
It seemed, as sweeping was resumed with measured swish in full attune, that something might be said to correlate the many interesting thoughts about the scene at hand. And so, in time, wind rivers of the Grand Canyon reflect themselves in Nature Notes.
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