A CONTRIBUTION TO THE STUDY OF ICE STRUCTURES 



II. THE LAKE-ICES 



1. PRELIMINARY 



Ice from the lakelets received most attention. There are many such small basins 

 on Cape Royds Peninsula, as will be noted by referring to the sketch of the neighbour- 

 hood prepared from the plane-table survey of Professor David and Mr. Priestley (see 

 The Heart of the Antarctic, Vol. I, p. 131). 



Much of the interest in the ice from these lakes centres in the fact that the waters 

 of the lakes illustrate various degrees of salinity and consequently the ice shows con- 

 siderable range of structure. Some of the lakelets are much Salter than others, ranging 

 from quite fresh-water basins to others as salt as the sea. In the case of the latter, 

 highly concentrated brine residues are developed in the course of freezing, which them- 

 selves eventually solidify after arriving at the cryohydric concentration. 



(a) Causes contributing to the Accumulation of Saline Matter in the Lakelets. 

 Three contributing causes are likely to have operated in furnishing the salt. 



(i) Salts carried on to the land as spray from the sea during gales in the summer 

 and saline snow from the floe blown on to the land during the winter. 



(ii) Leaching of salts from the upraised marine muds which, it would appear, at one 

 time covered the whole of the peninsula, and remnants of which are still to be seen. 



(iii) Leachings from the alkaline igneous lavas of the neighbourhood. 



Without entering into a discussion upon the subject, it will be stated that for obvious 

 reasons these three agencies must be regarded as contributing in the order stated. The 

 contribution blown from the sea is sufficient to account for all the salt. In fact it must 

 actually be held accountable for almost all. The contribution from the third source 

 must be very small indeed, for the prevailing temperature is too low for active chemical 

 decomposition. 



(b) Reasons for the varying Salinities of the Lakelets. 



In order to explain the freshness of some of the basins as opposed to the salinity 

 of others, it is necessary to draw attention to many agencies which must have been 

 operative. In the first place, as the winds which carry the saline matter over the land 

 are from the S. and S.S.E., the extremity of the peninsula must receive most of the 

 contributions blown from the sea. The neighbourhood of Blue Lake is more in shadow 

 in this respect, particularly as the head of Back Door Bay is frozen over excepting for 

 a very short period of the year. 



The wind distributing the salts over the peninsula is deflected somewhat by the 

 valleys, and so the contour of the land has some determining effect. A situation near 

 to the actual Cape itself, where most of the spray dashes over, ensures salinity. The 

 relative size of the catchment basins and the contained lakelets is important. 



The nature of the catchment and its disposition, whether it be rock or snow surface, 

 and whether it be more or less accessible to the sun is a matter of great importance, for 

 in all basins where there is much thaw in summer a considerable annual contribution 

 of saline matter will be brought in with the water. In order that it may become very 

 saline the lakelet itself must be well contained else an exceptional thaw would be liable to 

 sweep out the salts already accumulated. 



(c) The Nature of the Saline Accumulations. 



Besides the salt in the lakelets themselves there is always, in summer-time, much saline 

 to be observed over a great part of Cape Royds Peninsula in patches beneath, or in the lee 

 of, stones lying on the surface. In such positions it has the appearance of snow and 



