REQUISITE CONDITIONS FOR THE FORMATION OF 

 ICE RAMPARTS 



WILLIAM H. HOBBS 



University of Michigan 



In a recent paper 1 Mr. J. B. Tyrrell, late of the Geological Sur- 

 vey of Canada, has made the assertion that though he has now for 

 many winters made observations on and about the Canadian 

 Lakes, he has never detected any evidence of ice push against 

 shores as a result of expansion. He thus discredits the accepted 

 explanation of ice ramparts. To one who has in other localities 

 seen the ramparts in process of formation from this cause, it seems 

 important to supply an explanation for the failure of such an expe- 

 rienced and careful observer as Mr. Tyrrell to observe the same 

 phenomenon. 



The quite obvious fact is that ice ramparts are greatly restricted 

 in their occurrence, a number of special conditions being essential 

 to their formation. Mr. Tyrrell's paper fortunately shows that 

 some of these conditions were lacking in the districts which he 

 studied. 



In order that these requisite conditions may clearly be under- 

 stood, it will be necessary to give in brief outline the theory of 

 formation of normal ice ramparts through ice expansion. The 

 initial ice cover of the winter season on our northern lakes usually 

 forms with only moderately cold air temperatures. These may 

 be assumed to be but a few degrees below the freezing point, and 

 the cover, once formed to a thickness of an inch, grows quite slowly 

 from the under surface. After it has acquired a considerable 

 thickness, the arrival of one of the "cold waves" contracts the ice 

 cover by lowering its temperature through contact with the colder 

 air layers. Under this contraction fissures open in the ice to the 

 accompaniment of loud rumblings, water rises to fill them and is 



1 J. B. Tyrrell, "Ice on Canadian Lakes," Trans. Can. Inst, (iqio), IX, 1-9 

 (reprint), pis. 1-6. 



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