Before I tell you about another dramatic day in the field, here's a choice clip of our base town Amecameca. Lest we forget just how interconnected Popocatepetl volcano and this cool little town's residents are.

(This video has no sound)

Today we travel to a station in Tlamacas, 4,000m up, and on the way the subject is raised of Thursday and Friday's 5,000m climbs. 'What do we do if someone fails?' says Chiara. Hugo discusses the severity of symptoms and probability of sickness increasing with numbers. I suddenly feel the opportunity to climb slipping away. But altitude sickness is not something you can take sole responsibility for. If you get sick, the whole team is affected. So it's clear who should stay and who should go.

For now though, we travel together and hit the point in the road where a deep volcanic ash becomes our path forwards. 'We can drive a little further, then we walk' says Hugo. With that, our four wheel drive tries to engage it's four wheels. On our right is a drop of say 20 metres. Our back right wheel decides the latter is the route this car is taking and Hugo's passengers lose all colour in their cheeks. I bail without hesitation and we all attempt to push the car to safety, walking boots slipping ever nearer toward the drop. Purchase achieved, our lungs recover and our nerves unjangle.

Getting stuck is the pastime of a true geologist.

Where are we? It's a landscape I've never seen before, never thought existed. 'We're on the moon,' says Dave grinning.

Ash, more high altitude Sacaton and mounds of alien-looking mosses. A perfect location for a 70's Bowie video.

The conversation stays dark like the volcanic ash we tread as Dave shows me how to grip a walking pole so as not to break my wrists if I fall. I appreciate the technique and continue the hike to the station. My heart is racing but my pace is slow. Hey altitude, nice of you to drop by again.

Chiara steams ahead on a full recovery. Last one up writes the blog.

We're on the south west side of Popo and as we reach 4,000m Hugo needs to inform Cenapred (National Centre for the Prevention of Disasters) of our wish to collect samples. The monitoring equipment they use will pick up our hammering and - possibly - even our footsteps. Negotiations take place and we continue.

Hugo points out an incredible face of bi-colour lava. 'Look at the layers, says Dave. 'Shows incredible flow.' Hugo, armed with hammer smashes clean samples for everyone. 'It's between 1,300 to 2,000 years old. Two generations of magma, perhaps. 'The excitement is palpable, our dark thoughts are shifted.

Undeniably beautiful but I wouldn't want to carry a slab at 4,000m.

On our ascent to the station we see some fabulous scoria. One of the major igneous rocks, lightweight and extrusive. I'm sure I see Dave skip. And there were definitely three 'awesomes' as he surveyed the rocks. But we'd not collected any as the ascent seemed our goal. We want some now, especially a large specimen we'd all cooed over.

To get it we need to descend and it's steep, loose and a little scary to Chiara and I. 'As we Italians say, 'If you don't have head, you give leg!' she says which means we have to go back and get it. 'It's FINE. Let's do a scree run,' says Dave nonchalantly. I check my walking pole straps to ensure non-breakage of wrists and we run down the slope after Dave who, arms outsretched and invigorated is shouting, 'Easy!' 

Altitude-enhanced snack packaging. Never gets old.

I've brought with me a friend's backpack that she took to Everest. Its roomy to say the least. I offer it up for the collection of the big scoria. Proudly I carry what Dave and Chiara were sure would make it into the Museum's collections or possibly a gallery. Ten glorious minutes of hefting it, then I beg Dave to carry it.

Before we head back to the jeep, we survey Friday's climb. The ten hour hike. We've fared very well today, quite elated stomping down from the station. Not even tamales can prepare the team for what's to come.

"It's so close, let's do it now," says Chiara.

After a 24hr door-to-door journey from London, Lee and I secure our hire car and take on the streets of Mexico City. The traffic carries us along as it weaves and bobs haphazardly; the pavements are alive with switched on, purposeful looking residents. We’re roused from our jetlag by the hustle and bustle of the roads but crash back down to earth the instant we reach the hotel.

It's bumper to bumper, the vehicles have indicators but I've not yet seen one lit.

There are approximately 24 million people living in Mexico City (that's almost 4 Greater Londons!) and it’s impossible to prepare for the field work ahead without considering the impact this volcano has had on the people that live in its shadow. 15 eruptions have occurred since the Spanish arrived in 1519 A.D. with an unknown quantity before. Then, after fifty years of quiet, in 1994 a series of earthquakes signalled that eruptions had started.

A cloud of ash could be seen over its peak and it fell on the nearby city of Puebla. Civil defense evacuated 19 villages (a population of 31,000 people) east of Popo. By Christmas of that year, the total number of evacuees reached 75,000 and a ban on climbing the volcano for non-scientific visitors has been in place ever since.

A local squeezes through traffic.

We make an early start and drive to Amecameca, the town we’ll use as our base from which to climb Popo. Chic’s ‘Le Freak’ and breakneck-speed Spanish pumps from the radio as we tackle the GPS and the ‘soup’ of traffic. The map and the actual roads don’t always match but wrong turnings show us more of a landscape I already love.

Municipal buses don't come any cooler.

Gentle hustle on the busy streets.

Popo was visible from Mexico City but as we travel out in our car, the built-up scenery subsides to be replaced by quarries and swathes of red earth as the volcano begins to dominate our view. If Lee climbs like he drives he’ll conquer this giant, no problem. I stare in awe at the smoke plumes rising from its summit and think, ‘Will my climbing boots melt up there?’

View from our car on the 115 to Amecameca.

Checked in at our base in Amecameca, we explore the town and gaze up at Popo. You find yourself wanting to see it from wherever you stand.

The bar at Hotel Fontesanta, with neon palms and cutlery timepiece. Oh, and Popo on the horizon. 

Sunset from nearby town San Pedro Nexapa

We’ve arranged to meet National Park official Agustin, to gain access to the park and get closer to Popo. Lunchtime’s late in Amecameca and by 16:00 we’re greeted by a hulking great man with a warm demeanour and an unhurried efficiency. Gabriella and Gisella run the education programme and agree to an escorted drive part way up Popo. Lee and I depart for lunch. You’ve never seen two people eat cactus quesadillas so fast or with so much excitement.

A winding 3,600m drive up to Paso de Cortes, our breathing begins to feel heavy, our heads light. In the thinning atmosphere, I feel oxygen rich and starved all at once. Coordination feels clumsy but our sight is fixed. Lee has climbed further to grab some establishing shots of Popo and has been noticed grinning uncontrollably by one of the rangers. 'Emotion' he says knowingly as he gestures toward him. Chiara and Dave arrived Friday night and the sampling begins on Sunday.

Popocatepetl: Don't hold your breath, you'll need it.

We arrived here by car and this is the closest view non-scientific visitors see. From here, another 300m drive up is Tlamacas and from there, the ascent on foot begins. It’s been so valuable to take in the landscape before the science begins, to spend a little time at altitude and with the people who live with this volcano.

‘It’s exciting to live so close to Popo’ says Nacho, one of the park rangers with an incredible smile. We smile too and whether this is in agreement or the lack of oxygen to our brains, I cannot say. One thing’s for sure, the next 9 days are going to be pretty wild.