Hydrothermal Raw Soils (Fig. 13.5) include two quite
distinct geothermal situations and marked differences in the
resulting soil properties. In areas associated with
alkali-chloride features, such as Pohutu geyser at Whakarewarewa and the Champaign pool at the Waiotapu geothermal area, the water that is erupting has an alkaline pH. As
the water flows out over the land surface and cools some of
the ions dissolved in the water, predominantly Si
4+ , precipitate out and gradually build up the land surface with a hard
silica sinter coating. The famous Pink and White terraces
(that were largely destroyed in the Tarawera eruption of
1886, although surveys show probable remnants of both
Fig. 13.4 Soil landscape of Rocky Raw Soil on lavas from Ngauruhoe erupted in 1870. The track runs through a ‘mounded’ levee landform
adjacent to a channel at right
Fig. 13.5 Hydrothermal Raw Soils at Whakarewarewa in Rotorua. The visible yellow sulphur deposits indicate the low pH, and boiling mud, the
high temperature, of these largely inhospitable soils. Pohutu geyser is playing in the background
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13 Raw Soils