ROCK AVALANCHES 



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Viewing this enormous rock pile from a distance, one is impressed withits likeness to a great tongue of some viscous substance. The singular, 

 billowy surface also suggests a slow, lava-like flow. All observed rock flows, however, have been of lightning-like rapidity. It is at the 

 head of Silver Basin, San Juan Mountains, in Colorado. 



less than a generation ago in the Cimmaron Creek Valley, 

 covering several square miles, and every living creature 

 in the stricken area was doubtless killed outright. The 

 scene of the slide was \-isited within a few days by Whit- 

 man Cross, then as now a geologist of the United States 

 Geological Survey, accompanied by a photographer. The 

 area had been well timljered, but the trees were all over- 

 turned, bioken down, or standing at various angles, pre- 

 senting a weird and grotesque picture. Slopes were 

 exposed bare and many fissures gaped widely. Yet this 

 slide. Doctor Cross says, was largely surficial — a soil sliji 

 rather than a rock or land slide — and not to be compared 

 to a real rockslide. In another locality in the San Juan 

 Mountains the C. H. C. Hill, near the town of Rico, 

 progressive slipping is actually in effect at the present 

 time and there seems to be no guarantee that the Cim- 

 maron slide may not at any time repeat itself at this 

 point. At one place near the town the stump of a tree 

 has been split apart since the tree was felled and the 

 two portions were recently observed by Doctor Cross to 

 have separated about 5 feet in a period of four years. 

 This earth crack was traced for several hundred feet. 

 Any unusually wet period, such as Doctor Cross believe^ 



to have caused the Cinimarcjn slide, may precipitate ,i 

 catastrophe at this point. 



It is the injection of the human element which largely 

 determines the importance of natural catastrophes. The 

 San Francisco earthquake a hundred years ago would 

 have been of comparati\cly slight importance because 

 but few j)eoi)le woulil have been affected. On the other 

 haiifl, were the New Madrid earthquake of a century 

 ago to now repeat itself, instead of terrorizing a few 

 scattered pioneers in the Mississippi Valley it would 

 probably kill a host of people, destroy big cities and 

 cause incalculable damage. The eruption of \^esuvius 

 or Etna is always a terrible calamity because of the 

 thousands of inhabitants clustering on the slopes of the 

 mountains : yet two years ago Mount Katmai, in an 

 almost uninhabited section of Alaska, erupted with far 

 greater violence than the worst \'esuvian outljreak and 

 since no one was killed it has Ijeen looked upon princi- 

 pally as a most interesting natural phenomenon. On 

 the other hand a pro>[>ective landslide of 40 or 50 feet 

 of earth a few years ago at Mount Vernon would have 

 been a national calamity. Fortunately this approach- 

 ing slide was taken in hand in time, the dangerous under- 



