Posted by: Tanmoy Chakrabarti | February 10, 2009

Of Sheep and Volcanoes – 2

Acknowledgment: This post is based on my discussions with the locals who know a lot about the region, guide books published by Lonely Planet, Fodors, National Geographic, internet research on Wikipedia and some excellent books of which most majorly is the book – Tongariro: a sacred gift: a centennial celebration of Tongariro National Park by Craig Potton, Andy Dennis, Veronica Black, Kevin Hackwell. Thus, please forgive me if you have already read about these somewhere written in similar forms. I am especially thankful to the researchers who have extensively studied and written about these things. I am writing these for my records and also for the benefit of the very few readers that I have. I am especially thankful to Mr. Kevin Hackwell for taking out his time and post a comment on my post. This indeed clarified some of my concepts. I hope to read some more about volcanoes in New Zealand. The Department of Conservation publications may be a good start.

Before I actually describe my trek, it would be interesting to recapitulate about the volcanic activities in the region that we visited. I prefer to probe a bit hard into the places that I visit and thus forgive me for doing the same.

While the oft talked about mountains of Mount Tongariro, Mount Ngauruhoe and Mount Ruapehu are the major volcanoes here, the entire region is actually a volcanic zone known as the Taupo Volcanic Zone. There are around 22 volcanoes here resulting in crater lakes, hot springs, diverse vegetation and of course attractive tourist destinations. These mountains always bear the threat of erupting any time. Despite regular monitoring sporadic rise of smoke and falling boulders can be seen on a regular basis.

Lake Rotoaira, which lies between Lake Taupo and the foot of Tongariro

Lake Rotoaira, which lies between Lake Taupo and the foot of Tongariro

The Lake Taupo is the largest lake by surface area in New Zealand. The Lake is a composite crater formed much before humans arrived in NZ. The two most recent big eruptions of Taupo occurred 26,500 and 2000 years ago. The most recent eruption is one of AD 180. This is one of the largest volcanic eruptions that have ever occurred in history.

Lake Taupo belongs to the volcanic form of Supervolcano. This is a large volcano that usually has a large caldera (cauldron-like volcanic feature) and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulphur and ash erupted. They are the most dangerous type of volcano. The island formations on Lake Taupo are actually plugs of low-gas magma with the Lake being the caldera.

The Tongariro ranges lie at the Southern end of the Taupo Volcanic Zone and as mentioned the three mountains of Ruapehu, Ngauruhoe and Tongariro form the major volcanic points. Mount Ruapehu is one of the world’s most active volcanoes and the largest active volcano in New Zealand and it first erupted 250,000 years ago. Minor eruptions are frequent in Ruapehu, with at least 60 since 1945. Some of the minor eruptions in the 1970s generated small ash falls and lahars (mudflows). One can read about the destruction caused by a lahar, when one reads about disasters such as Armero tragedy in Colombia. As Mr. Hackwell mentions in his comment – Mt Ruapehu had two years of regular eruptions in 1995 and 96 during which there were numerous lahars. The crater lake emptied during those eruptions and the deposit of ash on the crater rim created an unstable dam. It took over a decade for the crater lake to refill and in March 2007 the ash dam finally collapsed sending a lahar down the Whangaehu River.

Lava tracts on the crater of Mt Ngauruhoe

Lava tracts on the crater of Mt Ngauruhoe

Mount Ngauruhoe is the youngest vent in the region, and first erupted about 2,500 years ago. It erupted 45 times in the 20th century, most recently in 1977. Those who have watched the movie trilogy ‘The Lords of the Rings’ may note that this mountain was used as the fictional Mount Doom. I am yet to watch the movies though.
Common Notice

Common Notice

Mount Tongariro erupted first 260,000 years ago. It consists of approximately 12 cones and Mount Ngauruhoe is actually a vent of Mount Tongariro. While Mount Ngauruhoe being the most active of the cones, the other craters of Tongariro have resulted in formation of lakes and unusual landscapes.

These mountains belong to the volcanic form known as Stratovolcanoes and are of the similar nature as Mount Fuji and Mount Vesuvius. These volcanoes are made up of are made of cinders, ash and lava.

Tongariro National Park is NZ’s oldest national park and was the fourth to have been established in the world. Consisting of the three mountain ranges of Tongariro, Ruapehu and Ngauruhoe this park also encompasses other lakes and craters created by volcanic eruptions.

Historically, in 1887, Te Heuheu Tukino IV, one of the most significant chief of the Māori gifted the major portion of the current national park, consisting of the peaks of Mount Tongariro, Mount Ngauruhoe, and parts of Mount Ruapehu, to The Crown, on condition that a protected area was established there. Subsequently further areas were bought to establish the National Park on the lines of Yellowstone National Park in the United States. In October 1894, the New Zealand Parliament passed the Tongariro National Park Act and the Park got built from early 20th century. Visitors to the Park increased post opening of railways in 1908 and roadways in 1930’s. The original inhabitants consider these ranges sacred and thus one has to take special care to protect the environmental sanctity.

The crossing

The crossing

This is the place we trekked on 7th February 2009, known as the Tongariro Alpine Crossing. The crossing covers 19.4 kilometres and provides an opportunity to go the summits of Mount Tongariro (1978 meters) and Mount Ngauruhoe (2291 meters). I think we climbed up till approximately 1950 meters before we started to come down. We did not aim to climb Mount Ngauruhoe since it appeared risky with our level of fitness. Even the Mount Ruapehu (2797 meters) climb is for the experienced climbers, though there is a very popular ski field there. However, we did not visit the ski field since our main objective was the Tongariro Alpine Crossing.

To be continued..



  1. Hi Tanmoy,

    Enjoyed looking at your posting this morning. I noticed that the first photo labelled “lake Taupo” is actually the much smaller lake Rotoaira, which lies between lake Taupo and the foot of Tongariro.

    I also noted the references to the way Lake Taupo was formed, etc.

    Unfortunately, there is a lot of partial understanding and exageration written about Lake Taupo and its history.

    As the first humans arrived in New Zealand 800 years ago the area was completely uninhabited at that time.

    The lake is a composite crater formed over a much longer period than you state. It is not the result of a single eruption 26,500 years ago – although there is no doubt that this was one of Taupo’s more recent really large eruptions.

    The comment: “Much of the geographical formation of Southern Hemisphere is said to have resulted from this particular eruption. ” is incorrect.

    The last Taupo eruption some 2000 years ago deposited a layer of pumice over a third of the North Island that is 100m thick in a few places (ususlly close to the lake), but is on average only a matter of tens of centermeters thick. This pumice layer fades out to just a centermeter or two at the edge of the “blast zone” – some 80 km from the Lake.

    A thin layer of the airborne ash has been found in marine deposits close to South America – but this hardly amonts to”much of the geographical formation in the Southern Hemisphere”.

    Mt Ruapehu had two years of regular eruptions in 1995 and 96 during which there were numerous lahars. The crater lake emptied during those eruptions and the deposit of ash on the crater rim created an unstable dam. It took over a decade for the crater lake to refill and in March 2007 the ash dam finally collapsed sending a lahar down the Whangaehu River (images at ,you should also be able to find good video of this on utube etc.)

    Glad you enjoyed your Tongaririro crossing. It certianly is one of the World’s great walks.


    Kevin Hackwell

  2. Thank you Kevin for enlightening me. I have undertaken changes in my post. If you do not mind, I shall like to get in touch with you to learn a bit more. Are you based in Auckland?

  3. Hi Tanmoy

    Can I suggest that you change the third sentence in the third paragraph from:

    One of the most recent eruption of Taupo was approximately 26,500 years ago in AD 180.


    The two most recent big eruptions of Taupo occired 26,500 and 2000 years ago. The most recent eruption is one of …..

    I’m based in Wellington.



  4. Thanks I have made the change.

    I wish you were in Auckland, I would have taken some time from you and met you. Both my wife and I are eager to give some time to work on Conservation matters.

  5. I am so happy that you have seen and enjoyed so much. This trip of yours has surely given a boost to your knowledge of geography. I hope your knee is happy too. Take care.

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