Show EROSION OF BRYCE CANYON 4 dy by K 11 weight hanger naturalist zion and bryce canyon represent unique phases of 0 erosion oslon ei the former a vertical walled U shaped canyon of great majesty and healt beauty Y cut pilm arlly by a river the latter a dowl or amphitheatre full ot of pinnacles pini nac I 1 a 0 or r monuments of such infinite variety and pattern to be almost unbelievable cut and carved primarily OY ay too myriad trickles of at water that bow after infrequent brainstorms rainstorms rain storms and melting snows it la Is the scenic features of those we io canyons that attracts most attention OLI tIOn but the chief message which each dach has hag to offer la Is ono that appeals not only to the aesthetic senses but also to t the understanding perhaps the highest enjoyment comes to one viewing these unique handiworks handi works of nature natzio when the story of their cre cie allons Is understood tills this s story ory Is primarily one ona of erosion hence wo we havo have asked each naturalist to tell the story each one from a different point of view we hope that each article will add something to the understanding of these natural wonders the main bryco bryce canyon Is rea really ily a great amphitheater composed of several small canyons leading down from the rim collecting together in the bottom it has no permanent stream of water flowing through it it Is a call canyon you of intermittent or ephemeral streams these streams vary in size and depend entirely upon the water horn from infrequent rainstorms brainstorms rain storms and melting snows iraln water is the principal agent of erosion assisted by wind frost plants and animals to a minor degree upon looking over the rim ot of the i canyon one sees a steep hillside j this steep slope has thousands of ota ravines ranging in size from those just visible to several feet in depth the smaller ones near the the topi top gradually coalesce into one large one near the bottom they have been formed by the rain water on its way to the bottom of the canyon during a heavy rainstorm thousands of trickles of water flow from the slope down these ravines collecting together to form a large stream at the mouth of the canyon pure water has very little cutting power as it passes over rocks but when armed with small particles of clay sand and silt it functions like a file or rasp cutting the limestone rock away at a rapid rate these thousands ot of rivulets remove the soft clay soil boll that is in its path and soon the bare hard rock Is exposed tile the grinding of tho the heavily loaded water carves deeper and deeper into the pink limestone cliffs until finally deep canyons are formed wall street through navajo aral passes Is one of the best examples the vertical walls of the individual canyons sometimes five or six hun died feet in height are gradually cut crosswise into separate parate Be parts by similar processes monuments or pinnacles of various shapes finally result some have a heavy capping at tile the top which resists erosion more than the softer layers underneath this produces undermining around the sides ot of the pinnacles pirina cles and they become so thin at the sides that tile the larger mass above tor top plea over the tha various monuments are being washed moro more slender blender and graceful each year continued action of the tha agents of erosion finally cause the tha monuments to disappear entirely when this stage is reached the landscape will be that of smooth rolling ridges separated by small ravines the monuments and walls 0 of bryce canyon when viewed from a distance appear to be very soft this impression in is due to the clay deposit that is found on the surface rain water falling on the monuments above picks dick up the fine clay particles from the various layers and as the water continues down the wall leaves part of its load as aa a dai de posit on the sides of the walls oi or pinnacles thus often hiding biding the real color of rock underneath the deposit Is 13 sometimes several inches thick the rate of erosion is comparatively rapid at the heads of the var various IOUs canyons conifers growing on tho the rini ilni have been undermined by the action ot at rain water and wind roots exposed tor for several feet on oil the canyon canion side are evidence that the canyon la Is eating gradually into the forest on I 1 the plateau above this rate recession is estimated osti mated to be ba about one halt half or three quarters inches peri per year tho the monuments erode away much slower slover estimated to bo be about the thickness of a thin piece ot of paper per year ground water functioning as a solvent as it passes through the tha underground rocks plays its part in the chemical decomposition of the rocks especially where it emerges from the at the toot of walls iron oxides are ara dissolved out wea weakening 0 the rock which soon crumbles to pieces the freezing of water ln in crevices produces a great pressure resulting in the flaking and chipping I 1 ot of tho the rock surface tho the I 1 nd st attas Tas awl and changing aaU EIng dally daily temperature play a part in the physical and chemical decomposition of 0 the rock the many small caves found in the tha perpendicular white just under the rim are probably pio bably due dua to the above agents to summarize a myriad trickles of water which flow following infrequent heavy rains or melting snows dig dep channels channe 1 leaving vertical walled ridges between them these in turn are cut crosswise la in a similar manner leaving pinnacles or monuments the monuments mou ments wear down in two ways principally by undermining of softer layers underneath by the agency of ground water frost drying etc preparing prepare ng the wa way for them to tall fall over but also by rain water vater falling on the top of the pinnacles and running down the sides As new ridges and monuments appear at the head older ones disappear near the bottom so that the not net result Is a gradually era gra duall movement into the plateau leaving a lengthening canyon behind zion bryce nature notes |