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Ngauruhoe - Mt Doom
GEOLOGY
The Tongariro National Park covers an area of young volcanoes all still active to some degree. Mt Ruapehu to the south, and the tallest of the three mountains, last erupted significantly in 1995 and 1996 including several lahars and the emptying of the crater lake. More recent activity, in 2007 was the generation of a lahar of an estimated 1.4 million cubic metres of mud, rock, and water that thundered down the Whangaehu river after the tephra dam holding back the crater lake burst. Later in 2007, activity also included a hydrothermal eruption where rocks were ejected, one of which crushed the Dome hut.
Mt Tongariro is the oldest of the three mountains, approximately 10,000 years older than Ruapehu, having first erupted around 260,000 years ago. Consisting of 12 cones, and containing the highest geothermally active system in the country, the most recent significant activity from Tongariro was an eruption of ash from Red Crater, central to the volcanic complex, in 1926. Hot springs and active steam vents can be found in a number of areas on the massif. Tongariro also has a number of explosion craters, some of which have filled with water, forming the spectacular Emerald Lakes, a popular lunch stop along the Tongariro Alpine Crossing track, and the tapu and quite acidic Blue Lake, sacred to the Maori people.
Ngauruhoe, in the middle, is the youngest of the three volcanoes, having begun formation only 2500 years ago. While most view Ngauruhoe as a separate volcano, it is actually a secondary cone of the Tongariro volcanic complex, and is currently Tongariro's main active vent. It presents today as a classic cone volcano, resulting from regular eruptions, and will be remembered by Lord of the Rings fans as Mt Doom, the part it played in the epic movie trilogy.
Mt Ngauruhoe was most recently active in 1975 and erupted 45 times last century. There have been over 70 ash eruptions from Ngauruhoe since 1839, and three lava eruptions witnessed over the same period, in 1870, 1949 and 1954. In 1954 Mt Ngauruhoe produced more than six million cubic metres of lava – the largest flow ever witnessed in New Zealand in historic times. Spectacular lava fountains played above the summit, and a sizeable scoria cone built up within Ngauruhoe’s crater.
 From early 1973 to 1975, activity became steadily more violent, pronounced by explosive eruptions of ash, during one of which it threw a 3,000-tonne block of lava 100 metres out of the crater. During the last and most violent eruption, gases streamed from the crater for several hours, producing a churning plume of ash that towered up to 13 kilometres above the crater. This column collapsed under its own weight, forming ash and scoria avalanches that swept down the flanks of Ngauruhoe, leaving trails of rubble in their wake.
Although Ngauruhoe’s eruptions have seldom been more than nine years apart, the mountain has been quiet since 1975 – the longest break in activity in its recorded history. Its steam vents have temporarily cooled, suggesting that the main vent has become blocked.
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THE TONGARIRO ALPINE CROSSING
To access this earthcache you will need to walk at least part of the 19.4km Tongariro Alpine Crossing track, considered by National Geographic as one of the top ten day walks in the world. The crossing takes approximately 6 to 8 hours to walk comfortably from the usual start at the Mangatepopo Valley carpark to the Ketetahi carpark, perhaps plus some extra time for stops along the way, like searching for caches.
If you plan to walk the whole crossing, you should be aware that you will need to be prepared to spend a number of hours in an alpine area with no shade or vegetation, and no drinking water. A reasonable level of fitness and outdoors confidence is required to undertake the walk and you should go prepared with plenty of water, food and warm waterproof clothing. A map and elevation chart are shown below.
It is a highly recommended walk very popular with overseas tourists, crossing geologically young and active terrain, and affording spectacular views of other mountains and the surrounding central volcanic plateau - just don't hesitate to turn back if the weather turns, and remember the emergency telephone number in New Zealand is 111. More information can be obtained on the official website.
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THIS EARTHCACHE
To claim a find on this earthcache you will need to perform the tasks described below. Failure to provide the required answers, which can be found at the puiblished coordinates, via email, or upload the required photo with your online log may result in your log being removed.
1 What formed the black rocks on which you are standing at the published coordinates, and when did this event occur (day, month and year)? The answer to this question must be emailed to the cache owner.
2 The Mangatepopo Hut and much of the lower Tongariro Alpine Crossing track is built on a lava flow from which eruption (day, month and year)? The answer to this question must be emailed to the cache owner.
3 Using your GPS unit, what is your elevation, or altitude, at the published coordinates? The answer to this question must be emailed to the cache owner.
4 From the published coordinates, or nearby, please take a photo of the Mt Ngauruhoe showing your GPS unit. Be careful not to reveal the answers to the above questions, and please make sure your GPS unit is visible in the photo. This photo should be uploaded with your online log.
You can log this cache straight away after you have emailed your answers to the cache owner, no need to wait for confirmation. Please include the name of this earthcache in the email - you'd be surprised how many people forget. Also, when contacting us with answers, if you want a reply, please include your email address. Any problems with your answers we'll be in touch.
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