OUR GREATEST NATIONAL MONUMENT 



229 



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Photograph by P. R. Ilagelbarger 



LOOKING ACROSS THE SAND-PLOW NEAR ITS TERMINUS 



This illustration is panoramic with the picture on the opposite page. The massive char- 

 acter of the flow and its relations to the undisturbed forest covering the hills beyond its 

 reach are evident. The fiery torrent consumed everything it touched (see page 241). 



torrent ran down the valley for about 17 

 miles. Even at that distance it was so 

 hot that, although it no longer utterly 

 consumed the forest nor started fires up 

 the mountain sides beyond its reach, it 

 still reduced every stick it touched to 

 charcoal (see page 224). 



The charcoal forests, uncovered where 

 the streams have later cut into the sub- 

 stance of the cooled and stiffened flow, are 

 extremely impressive witnesses of the 

 fiery avalanche that overwhelmed them — 

 far more striking than the utter barren- 

 ness of the upper valley, where the work 

 of destruction was so complete as to 

 leave the imagination powerless to recon- 

 struct the original scene. 



ESSENTIALLY DIFFERENT FROM A LAVA 

 FLOW 



In many places one can see the trunks 

 of the overwhelmed trees standing where 

 they grew, rooted in the ground, but 

 turned to columns of black charcoal. 

 Such charcoal logs are sometimes a foot 

 in diameter. In other places the mat of 

 vegetation that originally covered the 

 ground is preserved as a conspicuous 

 stratum of charcoal on top of the old soil 

 (see pages 224 and 226). 



Although the description will undoubt- 

 edly call to mind the condition of an or- 

 dinary lava flow, this fiery mass cannot 

 be properly compared with a stream of 

 molten lava, for it differed from a lava 

 flow in many essential particulars. Al- 

 though undoubtedly liquid in the begin- 

 ning, it did not long remain so, for the 

 escaping gases promptly converted it into 

 a suspension of innumerable solid frag- 

 ments buoyed up by the enormous quan- 

 tities of gas which were being given off 

 from within their substance. 



The physical behavior of the resultant 

 fluid was very different from molten lava, 

 for lava under the most favorable cir- 

 cumstances is a viscous liquid, moving 

 slowly, like stiff tar, whereas such a sus- 

 pension may run like water. 



Had the quantity of gas been less, the 

 material might have remained a liquid 

 lava of the conventional kind and hard- 

 ened into solid rock on cooling, but the 

 heavier constituents were so completely 

 disrupted that on cooling they became ash 

 and pumice similar to that formed in the 

 typical explosive eruption. When the 

 flow came to rest and cooled down, there- 

 fore, it became a fine-grained friable tuff, 

 easily cut into by running water, rather 



