Everyone knows about glaciers, those slowly flowing rivers of ice of
high mountains or the far north. Not all glaciers are of ice, though; some consist of
rocks. Rock glaciers, unlike ice glaciers, aren't limited to areas where the snow
piles up year after year until its weight compresses the lower layers into ice. Indeed,
rock glaciers appear to be most common in relatively dry regions of continental
climate. That, of course, describes our Chihuahuan Desert, and sure enough, we have
rock glaciers; in fact, in our own Franklin Mountains near El Paso. Our glaciers
probably aren't active now, but they share many of the characteristics of ice
glaciers. If you smoothed out the rough blocks of stone and painted the glacier surface
white, they'd pass. One explanation for their presence but current inactivity is
that they are relics of the last ice age. By this hypothesis, ice and snow infiltrating
jumbled fields of boulders rendered contacts between the rocks slippery enough to allow
them to slowly give way to the pull of gravity and flow down-canyon.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.
Lovejoy, E. M. P. 1972. Wisconsin boulder flow and its geomorphic implications, Franklin Mountains, El Paso County, Texas. Geological Society of America, Bulletin 83:3501-3508.