GLACIERS OF MOUNT RAINIER 



commonly, however, the south side of the column 

 becomes softened both by heat transmitted from the 

 sun-warmed south edge of the stone, as well as by heat 

 reflected from the surrounding glacier surface, and as 

 a consequence the table begins to tilt. On very hot 

 days, in fact, the inclination of the table keeps pace 

 with the progress of the sun, much after the manner 

 of a sun-loving flower, the slant being to the southeast 

 in the forenoon and to the southwest in the after- 

 noon. As the snow pillar increases in height it becomes 

 more and more exposed and the tilting is accentuated, 

 until at last the rock slides down. 



In its new position the slab at once begins to gen- 

 erate a new pedestal, from which in due time it again 

 slides down, and so the process may be repeated several 

 times in the course of a single summer, the rock shift- 

 ing its location by successive slips an appreciable dis- 

 tance across the glacier in a southerly direction. 



As has been stated, the slabs on glacier tables are 

 always of large size. This is not a fortuitous circum- 

 stance ; rocks under a certain size, and especially frag- 

 ments of little thickness, cannot produce pedestals ; in 

 fact, far from conserving the snow under them, they 

 accelerate its melting and sink below the surface. This 

 is especially true of dark-colored rocks. Objects of 

 dark color, as is well known to physicists, have a faculty 

 for absorbing heat, whereas light-colored objects, espe- 

 cially white ones, reflect it best. Dark-colored frag- 

 ments of rock lying on a glacier, accordingly, warm 

 rapidly at their upper surface and, if thin, forthwith 

 transmit their heat to the snow under them, causing it 

 to melt much faster than the surrounding clean snow, 

 which, because of its very whiteness, reflects a large 

 percentage of the heat it receives from the sun. As a 

 consequence each small rock fragment and even each 

 separate dust particle on a glacier melts out a tiny well 

 of its own, as a rule not vertically downward but at a 

 slight inclination in the direction of the noonday sun. 



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