Wednesday Rocks: #2


As I have mentioned before, New Zealand's North Island is rife with volcanic activity. I spent part of December and January on the North Island and part of that time was spent camping near Rotorua. Rotorua is part of the Taupo Volcanic Zone. Volcanism here is related to the subduction of the Pacific Plate beneath the Australian/Indian (depending on your source) plate. The volcanic zone has four recent andesite or dacite calderas which are, in order from west to east; Taupo, Maroa, Okataina and Rotorua. Maroa is the largest and Rotorua is the smallest (Cole, 1984). These calderas are situated in the Taupo-Rotorua depression and evidence suggests that the depression is the result of extension (Cole, 1984).

The photos below are from the Whakarewarewa Geothermal Village which is the happy marriage of New Zealand culture and geology. The village is home to the Tuhourangi/Ngati Wahiao people who use the geothermal springs for cooking, bathing and hot water. The village has been open to visitors since the beginning of the 19th Century and is definitely worth a visit. The people of the village are fantastic and the guides very knowledgeable. While we were at Whakarewarewa we had a hangi, a traditional Moari meal cooked using hot stones. At Whakarewarewa the hangi is unique as it is cooked using the heat from the geothermal system. One of the geothermal pools is also used for cooking. Food is placed in a basket which is lowered into the pool for about 7 to 15 minutes, depending on what's being cooked. 

The geothermal footprint at Rotorua is extensive with hot springs occurring on both the northern and southern shores of Lake Rotorua. Whakarewarewa is situated on the southern shore and the hot water found here ranges from about 90 - 110C. The composition of the hydrothermal waters at Rotorua suggests that there are three related hydrothermal cells. Whakarewarewa and a hydrothermal system which surfaces beneath Lake Rotorua are the hottest reaching temperatures in excess of 250C, at depth. The water flowing to the north of the lake is cooler at 220C. Ions dissolved in the hydrothermal fluids suggest that they interact with basalt and/or rhyolite at depth with basalt being the probable heat source for the thermal waters (Giggenbach and Glover, 1992).

Cole, J.W. 1984. Taupo-Rotorua depression: an ensialic marginal basin of North Island, New Zealand. Geo. Sco. London, Special Pub. p 109-120.

Giggenbach, W.F.  and Glover, R.B. 1992. Tectonic regime and major processes governing the chemistry of water and gas discharges from the Rotorua Geothermal Field, New Zealand. Geothermics pp 121-140

Parekohuru, most of the hot water used at Whakarewarewa comes from this spring. It is also the cooking pot.
Pohutu, Big Splash, Geyser (I think)

Whakarewarewa Village with Rotorua in the background

Mud pool with gas bubbles. Photo by Julian Joyce.

The hangi meal, cooked with the wonders of geothermal energy :) and very tasty

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