452 Transactions. — Geology 



volcanic belt. The existence of the inimitable terraces, and the 

 activities that prevailed over a large extent of country in their 

 vicinity, showed that the underlying forces were yet powerful 

 and far from being played out. 



Lake Rotomahana was a warm lake of varying temperature 

 at the time of the eruption. It had an area of 180 acres, and 

 was situated 1,080 ft. above sea-level, or 120 ft. below the level 

 of Lake Taupo. Near its northern end was the celebrated 

 Te Tarata, or White Terrace, and on the western side of the 

 lake was the Pink Terrace. Rotomahana communicated with 

 Lake Tarawera by means of the Kaiwaka Stream of warm 

 water, which entered the lake near Te Ariki, a small native 

 settlement. Rotomahana Lake appears to have been little more 

 than a lid covering in an intensely warm area — in fact, a crater 

 solfatara that slowly became filled with warm water. Round 

 about the lake were hundreds of hot springs that showed the 

 intensity of the pressures in the vicinity of the lake. Every 

 steam- vent, constant or not, is evidence of pressure. Hoeh- 

 stetter's map of Rotomahana, published in 1859, after his visit 

 to New Zealand, shows the location of most of the ngawhas. 

 puias, fumaroles, and solfataras that surrounded Rotomahana. 

 After the eruption, what was Lake Rotomahana became a huge 

 crater-like area, 515 ft. in depth, at the bottom of which stood 

 a small lake about 10 acres in area. Within the crater intense 

 activity prevailed : " the whole of the space seemed to be occu- 

 pied by a vast number of small craters ejecting mud. water, and 

 steam, all in a furious state of eruption : whilst ever and anon 

 an explosion that caused the surrounding hills to shake denoted 

 a more than usually violent outburst, which was accompanied by 

 a discharge of great rocks." But the whole of those eruptive 

 centres are now hundreds of feet beneath a lake that has increased 

 since the eruption to the depth of Lake Taupo. To the north- 

 east and south-west of Rotomahana deep chasms were formed, 

 and many changes took place in the surface - features of the 

 country. Without taking any estimate of the quantities of 

 material from the chasms and rifts, Mr. Percy Smith, the late 

 Surveyor-General, estimated that 600,000,000 cubic yards of 

 material was thrown out of Rotomahana alone, the crater 

 extending over 2,000 acres with an average depth of 515 ft. 

 The lowest point of ejection was Rotomahana, and the highest 

 Tarawera. 



Attendant upon the eruptions at Rotomahana and Tarawera, 

 and the formation of numerous craters of explosion, were a 

 number of earthquake-cracks in the vicinity of Waikorua and 

 Pareheru. Two photographs of these were taken by the late 

 J. C. Blvthe. an old friend of my own. who was at Wairoa at 



