648 THE FRESH-WATER LOCHS OF SCOTLAND 
the lake immediately started to rise. For years some of the water 
found exit through cracks in the tuff filling the creek bed, but when 
the lake had risen 42 feet the water flowed over the dam of tuff 
which prevented its exit along the old channel and broke much of 
it away, so that the level is now 11 feet below its maximum. Low 
cliffs marking the former level of the lake testify to the changes 
which its surface has undergone. Maclaren, of the Geological Survey 
of India, expresses a doubt as to the correctness of the views of Suess ^ 
regarding the necessarily deep-seated origin of geyser water, and 
contends that such waters may be of quite superficial origin, quoting 
the instance of the Waimangu geyser in support of his theory.^ This 
great geyser, discovered in 1900, which remained in active eruption 
for over four years, became dormant on 31st October and 1st November 
1904, the very days on which the pent-up waters of Tarawera Lake 
overtopped their barrier. 
Lake Rotomahana lies south-west of the Tarawera range, in 
about lat. 38° 20' S., and occupies the site of an immense crater, which 
was apparently the most active point of the Tarawera eruption in 
1886, when the exquisite siliceous pink and white terraces were de- 
stroyed. Immediately after the great outburst there was comparatively 
little water distributed in a number of small ponds in the huge hole, 
but with no outlet. The water gradually rose, and to-day is still 
rising, though much of the water entering the lake must find some 
subterranean outlet. It is a sheet of dirty, muddy, green water some 
3J miles long by less than 2 miles broad, and with a maximum depth 
of 427 feet. The boundaries of the lake correspond with the walls of 
the crater. Thermal action is at present limited to the western end of 
the lake, where, however, there is abundant evidence of the proximity 
of a heated interior in the great columns of steam ascending from 
the cracks in the stratified tuff beds. A warm stream enters the 
south-western end of Lake Rotomahana, formed by the junction of 
two steaming cascades which flow from the craters of Inferno and 
Waimangu. 
The temperature of the lake in the Inferno crater is about 180'' 
Fahr. (82° C), and its surface is rather less than 2 acres in extent. It 
emits almost continually steam charged with hydrogen sulphide. 
In 1899 Echo Lake crater contained a lake almost a quarter of a 
mile in diameter, which has now diminished to a small pond a few 
yards across, lying at the base of a cliff of variegated tuff. The floor 
of the remainder of the crater is formed by a surface of tuff hardened 
mainly by silica, but partly by incrustations of alum ; through this 
1 Suess, "Hot Springs and Volcanic Phenomena," Geogr. Journ., vol. xx. 
p. 518, 1902. 
'-^ Geol Mag., ser. 6, vol. iii. p. 511, 1906. 
