102 Br. Bu Riche Brelkr—Thc Mety'elen Lake. 



been seen empty at any time, is per se of no value unless it is also 

 shown that it was seen full the day or a few days before ; other- 

 wise it may, according to the season, have been empty for months. 

 The following are the years (since 1870) in which the phenomenon 

 has been recorded, 1 the total emptyings in eight to twelve years 

 being marked with an asterisk, while the cases of the lake being 

 seen about half full are omitted, because this, as already shown, is 

 its normal condition. It will be observed that the phenomenon 

 occurs always between June and September, an additional proof 

 that it is essentially clue to meteorological causes: — 1871. August, 

 1872. 1873.'- July, 1878.* June, 1882. August, 1884. August, 

 1885. September, 1887.* June, 1889. July, 1890.* July, 1892. 

 September, 1894. September, 1895.° 



Until recently, when the lake exceeded its ordinary maximum 

 level before it had forced a passage through the Aletsch glacier, an 

 overflow took place over the low saddle to the east towards the 

 Viesch glacier, about 770 metres or 2540 feet below the level of 

 the lake. In both cases the sudden rise either of the Aletsch or 

 of the Viesch torrent occasionally flooded part of the Ehone valley 

 above Brieg; 2 and it is with the view of eliminating this danger 

 that, the outlet of the lake to the Viesch valley has recently been 

 artificially lowered about 7 metres, or 23 feet, by a tunnel driven 

 through the low divide, about 700 yards in length and two square 

 metres (21 - 4 square feet) in section, which is intended to drain and 

 discharge on the Viesch glacier the overflow as soon as the lake rises 

 about three metres (ten feet) above the level at. which the lower and 

 upper basins unite. The overflow of which the lake will thus be 

 relieved is about three million cubic metres, equal to about one-thiid 

 of its volume at maximum level. 



It is. however, evident that although this artificial drain will 

 greatly mitigate, if not altogether prevent, the contingency of 

 damage, a discharge through the Aletsch glacier will always be 

 liable to occur whenever the ice-wall has become sufficiently porous 

 or undermined to yield to the pressure of the water. 3 Thus, while 

 rendered practically harmless, the Merjelen lake will still retain the 

 special feature which makes it unique among the glacier lakes of 

 the Alps. 



1 The data up to 1890 are derived from the lists ffiven by M. Ph. Gosset aud by 

 Prof. F. A. Forel (Jahrbuch Swiss Alpine Club, 1887 to 1890, p. 356, and 1S90 

 to 1891, p. 358) ; those up to 1895 are collected by myself. 



2 Formerly, the cowherd who first arrived in the Ehone vallev with the news of 

 the lake having emptied itself (the distance from the lake to Brieg being about nine 

 miles) was rewarded with a pair of new shoes. 



This actually happened on the 23rd September last, when the lake had risen to 

 within 50 centimetres (1-6 foot) of the floor of the overflow tunnel, and then, as ii to 

 show its contempt for this work of man's hand, emptied itself again through its 

 natural channel, the Aletsch glacier. The committee of inspection which was on its 

 way from Brieg, expecting to see the overflow tunnel in operation, arrived on the 

 24 th September only to find the lake empty. 



