Aconcagua 2 of 4: Acclimatisation

In 2. Aconcagua, South America, Project 7in4by Steve

Why Waste Time Acclimatising?

Since arriving at Aconcagua Base Camp (Plaza de Mulas) last Tuesday, we’ve spent the past few days acclimatizing. But why do we need to acclimatise?

At 6962m, Aconcagua is the 2nd highest mountain out of the 7 Summits and the highest mountain in the world outside of the Himalayas. It is not an overly technical climb by the route we are taking but the altitude does make it a serious undertaking. For us normal sea level dwellers, if we went straight from sea level to 6962m we would likely fall unconscious and without intervention, die. Obviously an undesirable outcome, so we need to acclimatise. But before getting into acclimatization, what is the oxygen effect at altitude?

There is a common misconception that at altitude there is less oxygen. This is possibly due to Everest movies where they talk about “lack of oxygen”. But this is actually false. It is the pressure that is changing not the amount of oxygen. At sea level, there is a pressure equivalent to approximately 10m of water pressing down on us all the time (101.325 kPa to be precise, average atmospheric sea level pressure). This is due to the weight of the column of air above us. When you climb up a mountain, there is less air above you hence the pressure drops. As the pressure drops the air expands, so there are less molecules of air for any given volume, also known as Boyle’s Law or P1V1 = P2V2, a formula I use almost daily at work. There are also temperature and humidity effects but I won’t bore you with a science lesson.

So at altitude there is still 20.95% oxygen in the air, the same as at sea level, but the pressure is lower hence there are less molecules of all air constituents for any given volume, including oxygen. Basically the air is thinner. Take one breath and you get less air.

On Aconcagua, the average air pressure is approximately 43 kPa, compared to 101 kPa at sea level. So with each breath you breathe in, you are only getting about 43% of the oxygen you would otherwise get at sea level.

So in short, we need to acclimatise so our bodies can still function on this thinner air and so we come back down.

How Do You Acclimatise?

Well, the jury is out on that one. Different people have different views on the best way to acclimatise. In general, people will tell you to climb slowly (I am not a great proponent for that) and to not increase your sleeping elevation by more than 1000ft per day. There are also new systems people are now using such as altitude tents and altitude training masks to try and pre-acclimatise at home. I’m not going to comment on those as I have never tried them. But what I find that does seem to work well for me is the old, tried and tested, “climb high, sleep low” theory. Climbing higher to new altitudes each day and returning back down lower to sleep.

Climb High, Sleep Low!

After arriving at Base Camp at approximately 4300m elevation on Tuesday, Wednesday we climbed up above Camp 1 (Canada) to ~5300m and dropped back down to sleep the night. Yesterday (Thursday) we climbed up again, this time above Camp 2 (Nido) to a small refuge called Camp Berlin at approximately 5930m and again descended back down to Base Camp to sleep. It was a wonderful day out with 1630m of ascent followed by 1630m of descent back down to Base Camp to rest and sleep. On this rotation we also carried gear to Camp 2 and deposited it there to use when we come up to sleep.

It was a rapid acclimatization program, but it’s all about listening to your body and how you’re feeling. Climbing at these altitude we felt great and were moving quick so we’ve decided to take today as a rest day and to plan for our summit push.

The conditions on the hill at the moment are fantastic. There had been an unusually large amount of snow in the past few weeks meaning we were on snow and in boots and crampons from just above Camp 1 at 5200m. Over time this snow has now become hard packed which makes for much easier going compared to loose rock and scree which is apparently more typical on the lower slopes of Aconcagua at this time of year. On the descent however, from Camp 1 to the bottom there is a steep scree slope which we can run/skate down making for a very quick descent.

Exploding Chocolate and Splash Back

Another effect of altitude is that items sealed at sea level effectively become pressurised as you go up. Sealed plastic bags become like balloons.

Our duffles with expedition gear and food for the hill were transported to base camp via mules, a dirty dusty means of travel, while we trekked in. Upon opening our food bag I noticed dust throughout the bag. I couldn’t for the life of me figure out how it got in. I have awesome Sea To Summit duffles which are pretty much bomb proof. Even submerged in water they barely leak. I inspected the bag all over and there were no cuts or tears. And there was no way the dust particles could have got in through the zip. It was then that I noticed the dust had a sweet smell and tasted delicious…. don’t ask why I was tasting dust.

Along with our food I had a bag of chocolate drinking powder which upon closer inspection had exploded and deposited chocolate powder throughout the inside of bag. Everything was coated. It was a disaster (albeit a tasty one). I can’t survive on the hill without my hot chocolate. Back home I basically live on the stuff, going through a 1.2kg tin of Milo on average once per week, but have been known to polish one off in 4 days. But to be honest, most of it gets eaten straight out of the tin and never makes it as far as the cup.

Anyway, I needed to rescue my drinking chocolate so I went through the tedious task of slowly removing all the other items one by one, wiping off all the chocolate powder that I could, until I was left with just an empty duffle and a pile of chocolate powder in the bottom. I then carefully scooped all the powder into a zip-lock bag, with more than a few spoonful’s going straight into my mouth in the process. It was tiring work and I needed to keep my energy levels up.

Once I scooped out every last particle that I could, I then wiped out the inside of the duffle bag with my towel which now leaves a chocolate cologne every time I use it. At least I can sleep easy knowing I have hot chocolate for the hill.

And talking about wiping things clean, that leads me on to another topic – splash back. You can probably guess where I am going with this so if you want to stop reading now, please do.

You’re still reading….. ok, don’t say I didn’t warn you.

In Base Camp they have a few toilets, basically just small tin sheds the size of a Portaloo, positioned over a hole in the ground. In the hole there is a drum which gets removed and emptied periodically. The little sheds have a timber panel floor with a cut out in the middle and two oval bits of timber nailed down indicating where to place your feet to squat. Pretty much your standard outback long drop, except this was a short drop, and with the drum underneath retaining liquids, their inlaid the problem. Taking a No.2 was like bombing into a pool with unpleasant liquids rising back up out of the hole. The splash back was horrendous.

I’ve subsequently learnt the other toilet has a makeshift toilet seat which helps retain the splash back, so I know which one I’ll be using from now on.

Monitoring the Weather

With bags and bottoms clean, and some good acclimatisation behind us, we are now just resting in Base Camp and researching the weather for a good summit window.

“Go with the decision that will make for a great story”.


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