Leaving Huka Falls, we were intrigued by signage to ‘Craters of the Moon’ and thought it warranted a closer look. This fascinating steamfield is part of the Wairakei geothermal field, the largest in New Zealand.
When the geothermal Wairakei Power Station was built in the 1950s, underground water levels were lowered and the hot water from deep within the field rose to the surface, emitting steam through any vent it could find.
Wooden boardwalks have been constructed along the 2.4km walking trail to protect human feet from the heat of the soil and they are regularly moved as new vents emerge. Gravel tracks lead to viewing platforms for a closer look at the bubbling cauldrons.
As I soon found out, it is important to be aware of the wind direction when taking photographs. Being enveloped in a cloud of sulphurous steam is neither good for camera nor operator. There is a wide variety of thermal features but three main ones. Fumaroles are openings through which steam and volcanic gases escape and can vary in size and intensity.
The pressurized steam makes whistling, hissing or roaring sounds depending on the size of the vent.
The craters are most impressive. They are formed when the pressure beneath the surface increases due to a blockage of a steam vent. The resulting eruption of hot water, steam, mud and pumice causes the surrounding soil to collapse, leaving a deep hole or crater.
The condensed steam and acidic gas chemically alter the pumice soil giving it the stunning orange and red colours.
It seems that mudpools are not technically pools of mud. The steam, containing hydrogen sulphide and carbon dioxide, reacts with the surface water to form sulphuric acid. This eats away at the surrounding rock and turns it into a soft clay that bubbles and belches as more steam and gas tries to escape.
I hadn’t expected so much vegetation on a lunar landscape, few species can survive the steamy ground. There is a plant endemic to New Zealand, prostrate kānuka, that only grows in geothermal areas and the hotter the ground temperature, the more prostrate the plant. Numerous ferns, mosses and lichens that would normally only grow in the tropics thrive in these conditions, adding colour to an otherwise barren place.
Toward the end of the walk, there is a fabulous view of Mount Tauhara, a dormant volcano overlooking Lake Taupo less than twenty kilometres away.
Soon after, a steep track to a lookout rewards with an impressive vista of the geothermal field.
Being so close to a restless earth was somewhat disconcerting, especially with the White Island disaster, only three months before, still fresh in our minds. Visitors are reassured that the thermal activity is monitored regularly by scientists from the Institute of Geological and Nuclear Science.