Day five and we see a split in the team. The public engagement crew are town-bound due to our scientists traversing dangerous terrain at heights they've never been to before. I see the logic but I miss the buzz of the hike and reporting back first-hand. We travel as far as Tlamacas wth them at 06:00, me in the jeep asking them questions from UK students that are being relayed to me via phone, and all the while I'm eating a cheese and chilli sandwich. We're all tired but Dave and Chiara's day will push this exhaustion to its limit.

Still, it's vital to record their day for your good selves so I instruct Dave to take many photos, which you'll discover he was rather good at.

Popo, you never take a bad picture.

Rocky V: The return of the rugged outcrop. Actually, kinda like Stallone's face these days.

Chiara, Dave and Hugo cross a steep section of rocks roughly 30cm x 2m across, zig-zagging all the way. This in itself is tough going, those lungs in constant need of oxygen. But they're faced with an even steeper incline of pumice and loose ash after that and Dave gently laughs at the prospect. Slipping their way up, they are rewarded with reaching the snowline. A small patch of what once covered Popo to a greater degree, only to be reduced dramatically by the change in climate.

I'm fairly convinced this isn't a water stop. Hugo only stops to collect rocks.

The altitude sickness has lost it's bite for now and both Dave and Chiara are doing well. At least Dave can see straight away when he gazes up without the second or two delay he's been experiencing. Through his renewed vision, he spots a bread-crust bomb and as he photographs they hear a muffled, loud BOOM! The first explosion from Popo and I'm not there [shakes fist at sky]... A plume of gas drifts over the ridge and Dave remembers this isn't a mountain, this is an active volcano. And he's close enough to the crater to feel fear for the first time since being here.

The bread-crust bomb. Explain what it is or it'll break granny's teeth.

Meanwhile, I'd arranged to visit a local middle school in nearby San Pedro Nexapa to find out how the kids feel about living next door to Popocatepetl. The generous Gabriela and Gisela from the national park office had made this possible and as we turn into the gates I thank them. A sea of curious faces turn our way and I know from how they react we are in for a warm and funny visit.

Elsa, Marianna and Ana Paola had been chosen to speak with us and after shy introductions and a briefing that hopefully set them at ease, we set up camera. I didn't know what to expect as sometimes kids can be ambivalent to such real fears but the girls all showed it. They were more than aware from family members, the past dangers of Popo and, although very friendly, they were solemn on the subject. Marianna was particularly eloquent and agreed to appear with us on the live-link to the Museum's Attenborough Studio at 14:30 on Saturday (so check back with this blog as we hope that a recording of the event will be uploaded soon after).

Back to Popo and our scientists continue their climb ... the pumice under foot is 'Like standing on marbles' says Dave. Without poles? 'Nearly impossible.'

Two more BOOMS makes eight in the trek so far. Chiara, Dave and Hugo reach as far as they are going to climb today - 4,630m - where they'll take their first sample. They can see the stratification (arranging of layers) of the lava flows as they dip down into the valley.

Look at the strat on that.

The descent begins, back down to the snowline and Dave describes his footing as 'surfing the scree.' Much easier to slide down keeping the body stable than to scramble up it as he did earlier. He's keen to meet Chiara who's a little way off and make their way to the jeep after a 'cracking day.' Three or four more BOOMS in quick succession. Popo's really picking up the pace.

They descend further to 4,215m and feel the chill as the clouds descend. At an outcrop, they discover something new. A dark rock with really nice pink and white crystals of feldspar. Quite big crystals. They'd describe this as porphyritic and are both 'anxiously excited to find out why this rock is here and why it's different.'

The team made it back to base, safe and sound, despiite the frequent booms and rumbles that Popo made during their trek. Lee and I met them for dinner after a brilliantly guided visit by Gabriela to The Hacienda de Panoaya; home to a zoo, the international museum of the volcanoes, and a museum honoring Sor Juana Ines de la Cruz (Mexican nun and writer), who lived here during her childhood. Lee finished our visit in style with a post-lunch zipwire, crying out the word for 'mud' in Spanish to impress Gabriela with his learning.

Not my words, Chiara's, as we chat over a drink shortly after the arrival of our eagerly awaited Museum scientists. Seems Hugo (our man in Mexico and fellow scientific collaborator with Chiara and Dave) is a different kind of vulcanologist. His study of volcanic gases provides them with a rounded view of the outcrops we'll be visiting to collect over the next week.

A shakey shot but I was keen not to spook our weary travellers.

Barman Rudolph interrupts politely to tell us of two climbers who 'had trouble' on Popocatepetl two weeks earlier. A confusion of language or had they perished up there? Thankfully, it was a near-miss tale of being sure to inform people of your climb.

We take Chiara and Dave to a superb taco stall. On a blanket of coriander, busy lads fried indistinguishable meats. Tripe's popular but having tried it in the spirit of adventure, I cannot say why. Chiara enquires about our eating habits since arrival, 'No Montezuma's revenge yet?' We confidently shake our heads.' OK' she says, 'only it takes up to a week to kick in.' Momentarily anxious, I order another pair of tacos. We weave past a jumpy pack of dogs on our way back to base. The first collecting site is at sunrise, so it's time for heads down.

Chiara likes to make personal notes as well as scientific on all her field trips. She writes her first thoughts of Popo.

That same winding road and at Paso de Cortes, Chiara smiles and treads toward Popo. We both agree it looks forboding: so large and incredibly steep. The wind is up and it's cold too but the sun is spectacular, catching all the sharp contours of Popo and its neighbouring volcanoes. Hugo arrives and we begin a stone's throw away, clambering down to the first sampling area named Tutti Frutti because of the colouration of it's rocks.

Chiara consults a beautiful colour coded map showing Popo's past lava flows.

Chiara, Hugo and Dave observe the layers of volcanic deposits.

I said I'm hard rock, not soft - Chiara uses a gentler tool of Hugo's for an altogether gentler task.

To my surprise, absolute quiet descends. Collecting what appear to be soft rocks is a very sedate activity. Layers are numbered, samples are hammered lightly or scraped into bags and each one is carefully labelled.

Hugo and Chiara discuss how they collect and the age of this lava flow. Hugo states it happened 14,000 years ago. They visually identify those rock types they recognise and chat about the work of other collectors, recently here to study other aspects of Popo. It's clear Chiara is up to date on all that's written on Popo. If she's going to fully understand it, her own studies are made all the better for her knowing the work of others.

It's like scientific Simply Come Dancing watching Dave and Chiara collect. The sheer coordination.

Three outcrops in and we are on the roadside examining another lava flow. This time the rock is hard and Chiara raises her shiny new hammer. She's less than fond of this one: her favourite's been lost and this has a dreadful 'newness' about it. At 4ft 11 inches, appearances truly deceive as Ms Petrone proceeds to knock seven bells out of the basalt lava.

Be sure to put her on speed dial if you ever need a wall knocked through. It's seems a basic method but I'm told its a trusted one. But why hammer your way through rocks when there are so many of the same type around? 'To get to a fresher surface,' says Dave. Much more fruitful to study.

Beautiful crystals of feldspar (rock forming minerals) glimmer in the freshly exposed lava.

Three o'clock and lunchtime had arrived. I glanced up from the pistachio shells I was considering eating and we drove to Cholula, the town of 365 churches. Had there have been time Hugo suggested we counted them, but lunch was quick and we hopped back into the jeep to visit the last outcrop of the day. And what an outcrop it was.

Chiara and I, dwarfed by the gargantuan 2,000 year old lava flow from Popo.

The sheer height of this lava flow domiated our entire view and was for me, the most striking sight of the day. This is not to say I've become complacent at the sight of Popo but, for the first time, the scale at which the lava from the restless giant had once been hit home. It stood as a reminder of what it was capable of, what Chiara and Dave were hoping to one day shed some light on. Most of all it reflected the destruction it had brought to the people that once lived here.

A few rock samples were broken, bagged and again carefully labelled. Having Dave onhand meant at a glance, the gaps in the Museum's collection could be accurately filled. Hugo too, had sampled throughout the day, so as to duplicate what was collected. Tomorrow our plan was to climb higher and as we juddered violently in the jeep en route back to the hotel, a blinding red sunset appeared.