508 Transactions. — Geology. 



line that steam would rise and betray Euapehu as a slightly- 

 active volcano at a distance. But Euapehu does mount above 

 the snow-line, and the steam at first is used up for melting 

 the snow it meets. This is the obvious origin of the lake. 

 The cinder-cone is very excentric near the eastern rim of the 

 southern part of the main crater. There the snow would soon 

 be melted, and the temperature of the water might rise, if it 

 were not for the other sides of the cone, where (more especially 

 from the rather extensive inner slopes of the southern and 

 south-western parts of the main crater-rim) neves or glaciers 

 hang down, and, according to well-known laws of movement 

 of glaciers and neves, move towards the deepest place — that 

 is, the lake. Thus, whereas the steam has the tendency of 

 raising the temperature of the water, the sieves, of course, do 

 the reverse. The result must depend upon the relative power 

 of the two antagonistic forces. If steam from the depths be 

 plentiful, and the glaciers be slow, the warm water and the 

 steam rising from its surface may melt the snow at a certain 

 distance, and prevent any considerable amount of frozen water 

 from touchmg the lake ; and then, of course, its temperature 

 might reach boiling-point. In that case the steam from the 

 depths would not be condensed any longer, and the lake, under 

 such circumstances, might exhibit geyser-like phenomena. If, 

 on the contrary, the steam from the depths be scarce, or the 

 masses of snow travelling towards the lake be large and their 

 rate of progress fast, the temperature would be kept down and 

 no steam could escape, as it is readily condensed in the cold 

 or only lukewarm water. 



Euapehu, I think, may be fully as active as Ngauruhoe 

 (as I found it) without appearing so. There was snow in 

 the crater of Ngauruhoe, and if Ngauruhoe were higher there 

 would be more snow ; again, if the crater were larger there 

 would be accumulated snow ; and if the steam had to deal 

 with sufficient masses of snow it necessarily would form a 

 lake, which it does on Euapehu where the above conditions 

 prevail. 



It may be asked. What becomes of the water of the lake ? 

 A part, doubtlessly, evaporates ; but it seems very probable 

 that the Eiver Wangaehu receives water from the lake by 

 percolation. The lake is contained in a cinder-cone, situated 

 excentrically, at the south-eastern rim of the main crater. 

 The visible eastern surroundings of the lake are masses of 

 dark cinders, which, of course, are easily permeable. The 

 Wangaehu Eiver starts from the eastern slope of Euapehu, 

 and its waters, as well as the waters of the lake, are turbid, 

 and have a smell of sulphuretted hydrogen. Taking these 

 facts into consideration, there can, I think, be but little doubt 

 that this is the way the water takes. 



