The Primrose Terrace and the Wai-O-Tapu Geothermal Area

There are many places in the world where near-surface geothermal activity causes silicates to bubble up with hot water and then to be precipitated as the hot water trickles away or evaporates. Where these siliceous precipitates are deposited, impressive structures of delicate miniature pools and terraces are formed. Perhaps the most famous is the Mammoth Hot Spring terrace of Yellowstone National Park. In the southern hemisphere, New Zealand’s North Island has some of the most impressive geothermal features, particularly around Rotorua and Wai-O-Tapu.

The Wai-O-Tapu area includes a variety of natural features such as hot spring pools, bubbling mud pots, collapsed craters, and a sinter terrace known as the Primrose Terrace. This is the largest known sinter terrace (1.5 ha) in the Southern Hemisphere, since the Pink and White Terraces were destroyed in 1886 by the eruption of Mount Tarawera. The siliceous sinter flows in hot water from the Champagne Pool, which gets its name from the carbonic gases that bubbling out of the 73-degree water. Microbiolites and microstromatolites play an important role in the silicate precipitation by providing templates for silica precipitation. Around the Champagne Pool, various elements provide the colours of the rich pallet, including colloidal sulphur and ferrous salts (green), antimony (orange), manganese oxide (purple), silica (white), sulphur (yellow), iron oxide (red), and sulphur and carbon (black).

The Wai-O-Tapu area is associated with volcanic activity dating back to 160,000 years ago. The Champagne Pool is much younger, only about 900 years old, and the Primrose Terrace is believed to have been forming only for the last 700 years.