Mauna Kea – the world’s tallest mountain

At 10,000m from its oceanic base to the peak, Mauna Kea is the world’s tallest mountain. It provides an arduous high-altitude hike over barren volcanic terrain, where the numbers look straightforward but the lack of oxygen adds a considerable challenge. There’s a high chance of experiencing snow in Hawai’i (and an altitude headache!)

Total distance: 20741 m
Max elevation: 4196 m
Total climbing: 1499 m
Total descent: -1499 m

Let’s open with a very strong word of warning: do not underestimate this route. This is a high to very-high altitude hike with little opportunity to properly acclimatise. Altitude impacts people in different ways, and even the fittest of hikers may start to experience severe symptoms at the starting altitude.

The effects of altitude can be fatal, and in many cases the only option is to descend.


Mostly volcanic rock on a steady gradient, with occasional steeper volcanic scree making walking more arduous. The last 200m of ascent is on a road, but there’s not a lot of oxygen so it’s harder than one would think.

In good conditions, for an experienced hiker, the terrain, ascent, distance and navigation is straightforward. Managing the impact on your body is the greater challenge. In poor conditions – why are you even up there at all? Go to a spa, or head to the sunny part of the island to a beach, this hike is best enjoyed when you can see the view.

Check the forecast on the Mauna Kea weather center site: you’ll likely get a good view at these altitudes even with rain at sea level. We were lucky enough to have an inversion, holding the cloud base well below the starting altitude.


The hike starts at the Mauna Kea Visitor Information Station at 2,800m. You can drive up to it, which is where the first challenge lies: it can take less than an hour to get from sea level accomodation to 2,800m. This is not enough time to acclimatise to the altitude, so it’s best to spend some time at the VIS.

Acclimatize and Register

We opted to get to the start for sunrise, take some pictures, and generally faff around for 45 minutes to aid the process of acclimatization. Toilet facilities are available at the VIS 24 hours a day.

Park in the lower car park, then go to the main information station building and fill in a registration form so they know you are out hiking on the mountain. I don’t know what they do if you don’t come back, but they looked quite relieved when we rolled in just after sunset. At some point after dark they might come and haul your exhausted body off the trail, but please don’t let it get to that. Be sensible, and if it’s time to quit, you should quit (more on quitting later).

Sunrise at the Mauna Kea Visitor Information Station

Finding the Trail

Leave the Visitor Information Station turning right onto the main road and continue ascending. The spell on the road is brief – look for the 4WD track heading off the road to your left, marked “Humu’ula Trail”. This is is easily spotted just before the road turns from asphalt to gravel. After another few hundred metres the trail proper begins, branching off the 4WD track to the right and uphill.

While the main road takes long zig-zags up the mountainside, the trail climbs more steeply and directly, slightly to the west, mostly within the Mauna Kea Ice Age Reserve. This route soon puts cinder cones between the trail and road, providing splendid isolation from vehicular traffic. The trail is marked by metal posts every 500ft or so, and the gently worn path is easy to follow by itself. The terrain is rocky throughout and what little signs of life there are quickly disappear.

The first 600m provides the steepest ascent, but with limited technical difficulty. A few areas have steeper ash slopes, with the inevitable sliding back down with every footstep. It’s worth stopping to take in the views, give yourself more time to acclimatize, take on some water, and eat. At altitude your body starts to divert blood away from your digestive system to prioritize oxygen to your brain, so eat early.

A great view unfolds across the volcanic landscape out to Mauna Loa and the comparatively diminutive Kilauea beyond. Kilauea is the island’s active volcano, and as the baby of the bunch is still growing. One day, it too might reach the soaring heights of Mauna Loa and Manua Kea.


Crossing 3,500m, the gradient eases as the trail heads in a northwesterly direction between cinder cones. Views of the wide, open plain below give way to an other-worldly environment: high above the clouds, a vast rocky expanse extends around you. Monochromatic at first, vibrant orange and green hills come into view. On inversion days, a fluffy layer of cloud sits far below you, with towering cumulus congestus clouds foreshadowing the ground-level rain to come.

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Piles of basalt sit by the side of the trail; Mauna Kea hosted a basalt quarry used by ancient Hawai’ians, mined here and turned into tools in workshops on the volcano. The piles of basalt encountered here mark the site of one of the main workshops, the material destined to be turned into adzes (a tool similar to an axe), hence the name Ke-ana-ka-ko‘i, “cave of the adzes”.

Altitude Bites – Escaping the Mountain

At 3,600m, the route enters ‘very high altitude’ territory. The isolation from the road comes to an end, as track and trail start to converge for the final climb. Although hidden at various times by rocky outcrops, the summit area – and the long road up to it – is squarely in view.

Our group was collectively beginning to suffer. The slow, nagging, altitude headache was kicking in and the pace was dropping. We broke out the aspirin. The degradation in our pace had a compounding effect – altitude sickness increases with altitude and (initially) time, and due to our slow pace we were on the mountain for longer than expected, putting us into the 6-10h window where it starts to appear.

This proved to be the limit of one of our party, and it was time for him to quit. We began to look at escape options. At this point there were only really three options for our exhausted comrade: descend slowly on the route, climb another 300m to a trail which met the road, or head cross-country directly to the road and try and hitch a lift to lower altitude.

Having established that 1) was too risky and 2) was not physically possible, we split into two groups of two: one to continue the direct ascent, one to ensure our beleaguered colleague made it safely to the road and was able to hitch a lift back down. Fueled by energy drinks and with an energy gel (left over from Haleakala) as backup, we safely evacuated our team mate. This is an unmade, rocky, undulating route, but makes a suitable evacuation option when there’s no other choice. In poor conditions, carefully navigating to the east will allow you to find the road.

Note: employees at the observatories (and I assume tour buses) are forbidden from picking up hitch-hikers except in medical emergencies, but there are plenty of hire cars heading up and down in good weather.

Resuming the Climb

With our stricken compatriot safely heading off the mountain, the remainder of the pair (me!) returned to catch the second group and complete the ascent.

To be honest, I felt considerably less ill while I was chasing down the lead group than climbing slowly before, presumably due to the increased heart rate. I made good time, following the road briefly to the parking lot for Lake Waiau. A trail from there skirts Pu’u Hau Kea and climbs to 4,000m where it intersects the main trail.

Lake Waiau

The intersection of the main trail with Lake Waiau is obvious. From the main trail direction, heading to the left/due west requires a short descent before arriving at the lake. Hawai’ians consider this area to be sacred, so please don’t interfere with the various shrines around the lake shore.

Lake Waiau is one of the highest lakes in the United States. The volcanic rock on Hawai’i is usually unable to retain water at the surface, so having any lake at all, and especially at this altitude, is a wonder in itself.

The Final Pull

Returning from the lake, with the inevitable extra ascent the detour caused, continue on the main trail to emerge the other side of Pu’u Hau Kea, where the summit observatories come into view. For us, it was also the first time we encountered snow in the trail (in mid January). The trial descends slightly to the road, crossing the boundary of the Ice Age Reserve.

The summit is tantalisingly close. All that remains is 200m of unrelenting asphalt hiking, as the gradient increases to launch you up to the summit. All you have to do, if your altitude-addled brain allows, is focus on walking up.

The body is exhausted and gasping for oxygen, but the views are stunning, as you rise above the surrounding bulk of the mountain to look down on everything around. The monotony of the road itself adds to the feeling of fatigue, but the summit draws ever closer.

Finally arriving at the main summit area, you can take a look at the observatories on the surrounding hills. A sign requests that you not complete the hike to the true summit, as it is considered a sacred peak. A short hike will take you to the top if you decide to ignore this sign, or you can remain in the observatory area and consider it a job well done – the height difference is negligible at this point, and it all rounds to 4,200m.

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Return Route

After taking in the views, the conventional return route is to retrace your steps. This time, facing away from the mountain, you can take in the magnificent views as you walk.

For us, however, it was not to be. Another member of our group fancied taking her chances hitch-hiking down, and our progress had been so slow that we were running out of light. Rather than descending on the trail, with the risk of being stranded or getting lost, we elected to return to the start via the road. We were well-equipped, including with head-torches, but why increase the risk?

With our second team member heading off in a 4×4, the final two of us headed down the road in the hope of a nice sunset. Fortune was on our side – a shortcut runs alongside the main gravel zig-zags of the road, following some sort of drainage or service route. It also took us into prime position to watch the sun descend behind the clouds as the light faded.

With 400m still to descend, and another 30 minutes in the dark still to hike, we decided to cut our losses and make use of the train of 4x4s descending the mountain after sunset. One honeymooning Korean couple took pity on us and took us down the last stretch.

Stargazing & Weather

The MKVIS runs a stargazing programme, if the weather is clear. This is definitely worth sticking around for if you can. Unfortunately for us we could see the inversion breaking down during the day, with clouds growing ever higher. After 90 minutes waiting for the mist to clear at 2,800m, we returned to our car and headed out.

It turns out the huge clouds we had seen forming from above were wreaking havoc below, with visibility practically zero in the huge downpours and fog on the Saddle Road back to Hilo. The precipitation continued – 2 days after we were there, the summit road was closed due to the large amount of snowfall.

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