Hill. — Taupo Plateau and Lake. 461 



Lake Taupo was the centre of the disturbed area ; but crateral 

 rifts appeared along extensive lines of weakness, including Wai- 

 rakei and Roto-kawa. For many years the rift that narrowed 

 to the north-east was filled with thousands of steam- vents, that 

 have played an active part in cementing the pumice or in decom- 

 posing it by means of the acid gases that issue from the fissures 

 under high temperatures. As pointed out by Judd, the action 

 of acid gases causes iron, lime, and alkaline materials to be con- 

 verted into soluble compounds known as sulphates, chlorides, 

 carbonates, and borates, which on removal by rain leave a white 

 powdery substance like chalk in outward appearance, but com- 

 posed of almost pure silica ; and this action is everywhere going 

 on within the volcanic zone. For hundreds of years the rift 

 through which the Waikato flows from Lake Taupo was the 

 scene of intense hydrothermal activity not unlike what is seen 

 to-day along the line of rift extending from Tarawera to Pareheru. 

 On either side of the main rift there are deep transverse valleys 

 that are directly connected with the present Waikato Valley, 

 and in which hydrothermal action is still very active. If we 

 suppose that Lake Taupo was once much fuller than it is now, 

 there will be no difficulty in understanding the position of its 

 outflow from the lake. The river passes through soft pumiceous 

 material until it reaches lava-sheets farther down. The surface 

 rocks in the vicinity of Taupo are composed of pumice and hard 

 volcanic grits cemented together by the action of heat, and the 

 same kind of indurated pumice and grit stone go to make up 

 the material over which the river rushes and forms the cele- 

 brated Huka Fall. 



If we accept the explanation here stated as to the origin of 

 Lake Taupo, of its once much larger extent, and of its eventual 

 overflow into the extensive rift that was formed in a north- 

 east direction in the line of the Wai-o-tapu and Rotomahana, 

 it will ready be understood that Tarawera, Rotomahana, and 

 the active geysers and fumaroles in the Wai-o-tapu Valley but 

 represent portions of a great fracture or fault that has at times 

 affected the surface of the whole of the North Island. The high 

 cliffs bounding the western shores of Taupo are made up of 

 lava-flows. Even towards the top of the vertical cliffs at 

 Karangahape Point a band of red scoriaceous lava is clearly 

 seen from the deck of a steamer, although the band is 800 ft. or 

 more above the surface of the lake. Karangahape is 2,465 ft. 

 above sea-level ; Motuopa, to the south-east, on the opposite side 

 of the lake, is 1,632 ft.; and Mangamotu, to the north of the 

 Hinemaiai River, on the east side of the lake, is 2,060 ft. ; and 

 old crater-cups are numerous about the lake. Between them 

 stands Motutaiko, with its cap -covered deposit of fine powdery 



