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 (CO2) and hydrogen sulphide (H2S), will rise towards the surface. This is known as an acid sulphate geothermal system, because the hydrogen sulphide oxidizes to sulphuric 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.
There are two distinctive geothermal features at each end of Wai-O-Tapu mud pool. One is pools and vents fed by deep primary geothermal fluids which basically ascend directly to the surface. The other are pools fed from steam and gas that result from boiling deep under the earth at 10-100m. These interact with geothermal fluid and ground water to form discoloured pools and mudpots.
Wai-O-Tapu geothermal system is significant not only for being one of the very few systems not to be exploited and damaged, but also for it's interesting water chemistry. It is dominated by CO2 which encourages the precipitation of precious metals such as arsenic, antimony, gold and silver, but not of 'ore'grade. This is in the springs not the mud pots themselves.
The Earthcache:
In order to claim a find on this Earthcache, you'll need to email or send a message (through geocaching.com) answers to the following questions. Feel free to log your find in anticipation- we'll let you know if there are any issues. Logs without the emailed answers may be deleted. In addition, it is also preferable that you upload a picture of you or your group and your GPS with the mud pool in the background.
1) Estimate the width of the geothermal features here in metres (hint: the info board will help)
2) Describe the smell of the area in your own words, and what do you think is the cause?
3) Describe the appearance of the mud pool on your visit, e.g. thick & sticky with small mud volcanoes (dry conditions) or dark boiling water (wet conditions)
4) Estimate the temperature of the water and mud (hint: the info board will help)
5) Optional: Upload a photo of you or your group and your GPS with the mud pool in the background
