Mauna Loa day hike via the Observatory trail

Hiking United States

A little background about Mauna Loa

At 4169 m Mauna Loa is the second-highest peak on the Island of Hawai’i. It’s also the tallest and most massive mountain in the world. While there’s a road up to its neighbour Mauna Kea (at 4205 m the highest peak on the island), getting to the top of “the long mountain” is a bit more of a challenge.

Let’s quote my guidebook for a moment:

Getting to the top of Mauna Loa is tough, no matter which way you slice it. […] You can do it the hard way or the very hard way – it’s your choice.

The hard way is a 3-5 day hike. I only spent five days on the island, so this option was out. I had to look into the second one:

The other way is a tough 13-mile-round-trip day hike from the Mauna Loa Weather Observatory off Saddle Road. […] count on altitude sickness from starting so high […] you can do it in a day, if you’re into punishment […] It’s always cold up there, and snow can come any time of the year without warning. Altitude sickness is common, even among the fittest.

This comment comes from one of the best guide books, I’ve ever used and folks, who don’t seem to dramatize things. I also met a Scandinavian hiker on Mauna Kea, who told me he tried the hike the day before but had to turn around, mainly because he did not bring the right shoes. I would not have wasted much thought on this, but he also told me he summited Cho Oyu (8201 m) in winter. Having someone with that level of experience say the hike you plan is challenging, makes you wonder if it’s such a great idea.

I did some research on it and had three concerns: length, weather and altitude.


The trail is about the distance of a half marathon (return), and the official sign at the beginning of it puts the summit hike at 10-12 hours, most tour guides list it at 10 hours, while some guys do it quite a bit faster. I’m not a slow hiker, so I was confident that even in the worst case, I’d be down before sunset as long as I start early enough (sunrise is around 7 am).


The weather is a bit trickier. The clouds that build around Mauna Kea and Mauna Loa almost every afternoon give you an idea of how foggy, cold and uncomfortable it can get. And while it feels surprisingly warm in the sunshine, temperatures still drop well below freezing not only at night. In short, I made sure to check the weather report to pick a clear day for the hike, but also prepared for the worst (brought my winter hiking gear). During my ascent, I found some hideouts that would allow you to sit out a storm, but I would rather not have to try.


The biggest challenge is the altitude. 4000 m isn’t high compared to other mountains, and if you acclimatize well it shouldn’t be a big deal at all. The trouble on Hawai’i is that many people (including me) don’t have or don’t take the time to do acclimatization properly. Most of the places to stay are along the coast and around sea level. That means, if you don’t camp at higher sites, your body will have to endure an altitude difference of around 4000 m in just a couple of hours.

My lame attempts to get at least some form of acclimatization were visits to the Mauna Kea Visitor Center (2804 m), Mauna Loa Observatory (3370 m) and the Mauna Kea summit (4205 m). I tried to spend as much time there as possible, but everything was still done by car in quite a rapid pace. I visited the start of the hike near the Mauna Loa Observatory the day before my summit push. The reasonable choice would’ve been to camp there for the night (probably in the car). I decided against it and went back to sea level to spend the night. If you want to enjoy all parts of your summit day, DO NOT DO THAT!

The most important thing at high altitude is to drink enough. The air is dry, and there’s no water on the mountain, so prepare for carrying ridiculous amounts (I think I used somewhere around 6 litres during the hike). I had a small water bottle in my hand and was drinking from it regularly. Whenever it was empty, I refilled it from one of the larger bottles in my backpack. I also used chewing gums (supposedly chewing helps with the difference in air pressure) and low dosed aspirin pills to prevent and ease some of the symptoms of altitude sickness.

There’s water with added oxygen, that’s been advertised for some years now. Maybe hiking in altitude could be a use-case for it. I only thought about it during my hike, so I didn’t try. It’s likely more a marketing gag than being effective anyway. Then, of course, there are all forms of bottled oxygen (as the social media guys of one company pointed out to me after posting my summit photo to Instagram), but that’s a bit over the top for anything lower than the Himalayas. It’ll help for sure, but better spend more time on acclimatization instead.

UPDATE: Later that year, I learned about WMH breathing. If you’d ask me today, that’s what I’d recommend.

The hike

I start at 4:45 am and frive up Saddle Road to the Mauna Loa Observatory Road, a narrow 28 km road winding up to the Observatory through endless, awe-inspiring lava fields. The road has been repaved recently, so it’s quite enjoyable to drive, but you need to be careful at the various blind spots (although traffic coming down the mountain is unlikely so early in the day).

After arriving, I prepare for the hike and start shortly after the 7 am sunrise. The trail begins right where the street ends. You follow a dirt road for some minutes before the path turns to the left and south up through old lava, a style of track that will continue for most of the hike. The trail leads through interestingly shaped lava formations. It’s mostly marked only with rock cairns (ahu) easily visible in good weather. Sometimes, you’ll follow an old dirt road or a comfortable trek over greenish looking sand. However, most of the time, you struggle through harsh and rather unforgiving lava terrain.

I didn’t know how the altitude would affect me, so I started slower than usual, making sure not to over-pace.

After about 6 km there’s an intersection with the trail to the Mauna Loa Cabin. I follow the 4 km long Summit Trail to the top of the mountain. It’s a long, very gradual ascent and I begin to feel the effect of the altitude (or let’s say my lack of acclimatization) somewhere around the 4000 m mark. I get a minor headache and realize that calculating the remaining time to the summit (based on my average speed and the distance still in front of me) suddenly becomes challenging. Everything takes a bit more time at “high” altitude. I’m relatively close to the summit, so I decide to push through and only turn around if my condition gets worse. Shortly before the summit, I get the first view down into the vast crater. It’s a big WOW moment and worth all the struggles to come here.

A couple of minutes later (around 11 am) I reach the summit. I take some pictures and then quickly begin to head down again.

Descending the Summit Trail is tough. The signs of altitude sickness worsen, and the trail stays around 4000 m altitude for quite some time, giving you no option to lose height as quickly as you wish. My foot gets stuck under a rock in a moment of carelessness, and I fall face forward onto the hardened lava. My hands manage to stop most of the fall, and I get away with only minor bruises and cuts (lava rock creates nasty scars). After this incident, I slow down again and eventually reach the old dirt road at around 3800 m. From here on, it’s an enjoyable hike, and I start to realize my accomplishment. In a steady pace, I reach the Observatory Road around 2:30 pm. I take 4 hours to ascend and 3,5 to return down. If you know the trail, are reasonably fit and well acclimatized, I’m sure you can do it a whole lot faster.


This hike has been a very humbling experience. The landscape is breathtaking and beautiful. The scale of Mauna Loa is still hard to grasp, but hiking (and driving) on it for so many hours starts to give you an idea just how large it is. It’s not a technically challenging hike, and at lower altitudes, this could almost be called a “walk in the park”. The altitude and remoteness make it challenging nevertheless. It’s also worth mentioning that I didn’t meet a single person on the mountain all day (and it was a beautiful, sunny Saturday), so this is quite a remote and solitary place to explore.

Surprisingly, I don’t feel much muscle fever the days afterwards, but I have a general feeling of being worn-out and tired the day after the hike. Everything below 3900 m has been excellent, above that, it was tough for me (but that’s just the missing acclimatization). It’s been a great experience, and I am glad I’ve done it.