It’s mid-May and Mount Ruapehu is showing signs of a winter coat as early season snow is starting to settle around the tops. Being local, we get to appreciate the mountain all year round, and we do enjoy the contrast between summer and winter. However, unseen to most, it’s what happens high up on the Summit Plateau that continues to amaze, surprise and, increasingly, concern us.
Working as a guide with Adrift Tongariro, I get to spend a fair amount of time high up on the mountain throughout the year although that’s limited to around Dome in summer and the head of Whakapapa Glacier in winter. There’s a map further down in this post by the way, but I’ll get to that a bit later when I share some really interesting facts about the mountain. The point is that I don’t spend that much time high up on the northeastern slopes of Ruapehu. In fact the last time I was up around that side was in February 2021 when Debs and I spent an incredible few days exploring around upper Waihohonu Ridge and Te Heuheu. It was on that trip that we took the photo at the start of this post along with the one below.
This was the first time that we’d actually seen the north crater glacier lake up close-ish and we were totally transfixed by this translucent aquamarine gem.
Fast forward to May this year and Stew Barclay from Adrift pinged me a message to say “Hey, I’m heading up the mountain, want to join?” Given the current situation, our usual route up to Dome was out of the question so instead, we decided to head up Pinnacle Ridge to a spot below Te Heuheu summit. And for those of you who don’t know what situation I’m referring to, as I write this, Mount Ruapehu, an active volcano, is currently at alert level 2, a heightened state of volcanic unrest.
But, having checked the latest update from GNS Science, the organisation responsible for monitoring the mountain, and also having confirmed that our intended turnaround spot was just outside the 2 km (1.2 mile) volcanic exclusion zone, we didn’t have any major concerns.
I personally was looking forward to seeing the glacier lake again, given that this was May, and the lake had been there in February the previous year. So imagine my surprise when we got to the lookout to see this view instead:
The beautiful glacier lake had been replaced by a pretty sizeable ice cave. Here’s a closer view:
As much as it would have been incredible to go down and explore the entrance to the cave, common sense prevailed and after around 20 minutes and a quick lunch, we headed back down the mountain with many questions.
Doing some research on our return, it seems that the formation and draining of the north crater glacier lake is normal and part of the annual cycle. However, anecdotal evidence suggests that this lake has gradually been getting larger over the years, and that’s a worrying sign. Studies globally have shown a correlation between increased glacier melt lake sizes and glacier retreat and while the lake on north crater is relatively small and seemingly insignificant, it doesn’t bode well for not only the summit glaciers but also, in this particular case, Mangatoetoenui Glacier to the east.
In previous years, Mangatoetoenui was fed by ice in-flow from the summit but as you can see from the previous photos, the exposed rim of north crater now separates Mangatoetoenui from the summit, reducing its chances of long-term survival.
Glaciers are extremely sensitive indicators of both local and global changes in climate, and while Ruapehu’s glaciers have seen periods of retreat, equilibrium and growth in modern times, as things stand now, the mountain’s glaciers have retreated to an all-time minimum since records began. For people like Stew who have been climbing Mount Ruapehu for the past 20+ years, seeing these rapidly increasing changes first-hand is a sobering experience.
One mountain, several craters
Those of you who are reasonably familiar with Mount Ruapehu may be wondering about my reference to a north crater. As you will see on the standard topographical map below, there is no mention of a north crater on the summit of Mount Ruapehu. But did you know that at least three craters have been active on the summit in the past 10,000 years?
The Crater Lake (Te Wai ā-moe) and the vent beneath it is of course getting all the attention at the moment, but in the past, vents beneath what is now the Summit Plateau formed two craters, unofficially referred to as central crater and north crater. It’s not that obvious looking at the topo map but the satellite view does hint at the shape of these craters, still mostly under ice. How much ice? Radio Echo Sounding in the 1980s indicated that north crater had up to 130 m (427 ft) while central crater had less, about 60 m (197 ft).
Personally, both Debs and I are fascinated by the mountain and surrounding landscape, and recently I bought a copy of Karen Williams’ book, Volcanoes of the South Wind. If you’re interested in discovering more about not only Mount Ruapehu but the Tongariro National Park as a whole and the incredible forces that have shaped the landscape, we highly recommend this book.
Order a copy online at Project Tongariro and you’ll be supporting the Tongariro Natural History Society and the many conservation projects it undertakes in and around Tongariro National Park and the surrounding environs.