Waiotapu Mud Pool

July 15, 2014


Photographer: Phillip Lachman
Summary AuthorPhillip Lachman

One of the myriad of interesting and entertaining sights I saw while travelling New Zealand was the amazing Waiotapu Mud Pool. It's part of the 7 sq mi (18 sq km) Waiotapu geothermal area. As its name suggest, it's a large pool of boiling, exploding mud. Waiotapu occupies the site of what was formerly the largest mud volcano in New Zealand. The original cone, present until 1925, is now eroded and filled with water and mud.

Mud pools form when steam and gas rise underneath rainwater ponds. If deep geothermal waters are prevented from reaching the surface quickly, they may boil at depth, and a mixture of steam and volcanic gases (mainly carbon dioxide and hydrogen sulfide) will rise towards the surface. This is known as an acid sulfate geothermal system, because the hydrogen sulfide oxidizes to sulfuric acid. The acidic gases attack surface rocks, forming clay and the clay-rich soil mixes with the pond water to produce a muddy, steam-heated slurry, or mud pool. Steam and gases rising through the pool create bubbles of mud that form and burst. Rainfall affects the appearance of mud pools. In dry conditions, the mud is thick and sticky, and small mud volcanoes may form. When rainfall is high, the mud is much more fluid and the pool may look more like dark boiling water.
Waiotapu has a long history as a tourist attraction. While the area has been protected as a scenic reserve since 1931, a tourist operation occupies part of the reserve under a concession and operates under the name Wai-O-Tapu Thermal Wonderland. Photo taken on January 24, 2014.