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.

My post for today shall begin with a clip of what we've been priviledged to see every day whilst on field work in Mexico. Lee, Dave and I are all keen photographers and agree that there's a picture wherever you look. The light is literally perfect and there's barely a sound (bar that of scientists chipping rock) that can be heard in these wide expanses of grass, pines and volcanic matter.

(Note: this video has no sound)

After a high buzz start to the day, linking live to our Attenborough Studio to take excellent questions from sweet, keen students in a special event for schools, we visit our next outcrop (an area of exposed rock), a beautiful area called Tlamacas at 3,900m above sea level. No sooner had we piled out of the jeep than we see the cheery sight of Hugo, springing up like a mountain goat, to rocks roughly 10 metres high. I ask him as he descends a little later what is the highest he's climbed. 'K2', he beamed, 'at 7,300m.' I feel my lungs tighten and my admiration grow.

Hugo and Chiara investigate. Popo watches on in the distance.

I approach Dave to nosey into his activities by the exposed rock face. What have we here then? 'Volcanic rock. Feldspar. The likes we've seen here already. It's called Dacite.' I look on as he photographs the rock and ask how these images are then used. 'Pictures go alongside the collections. They show the features of the flow.' This has a snappy ring to it but a lot of sense too. Unfortunately Dave does not receive the same kind of imagery with samples given by others to the collection. 'If only' he smiles. 

I'm keen to know what finding similar rocks means in different outcrops. 'It's unusual not to have lots of change in a volcano but Popo's rocks so far are fairly similar. Chemistry should change over so many hundreds of thousands of years but they've not done so much here. The whole process is a bit random, so change should occur. This makes Popo pretty interesting.' The team chip away samples and discuss their finds. Hugo and Chiara pass samples between each other until Chiara pleads with hands full. 'Poor Italians, you only have two hands' laughs Hugo.

Chiara takes five to speak with Hugo's University TV Crew.

Our second outcrop is but a walk away. A steep walk. Downwards. Chiara must have some idea of how steep and she looks apprehensive. Her apprehension makes me excited. Are we going on a difficult hike? Hugo takes us to a spot, points down and says he'll meet us at the bottom. 'Don't follow the river for long as there are cascades. I'll meet you down there.' Our springy mountain goat not coming? Then I'm with Chiara on this one.

Cascades you say? Dave and Chiara following the river. And by river they mean where it used to be. I was looking for water. Doh.

I discover the senses figure highly in rock collecting. Firstly, as I sniff a fresh surface of exposed rock I discover that licking them is an everyday geologist pastime. Why? 'To taste the minerals' says Chiara, which seems a reasonable enough idea. Soon after I see Dave shaking his head in disapproval as he hammers a rock face in several places. 'No, no, no' he says as he slings the 'bad' rocks to one side. What gives, Dave? Well, sound is important too it seems. 'The thing you want is kind of a tinny sound when you hit it. Means its hard, unweathered and fairly fresh.'

You go first. No, you go first.

Our search for a particular rock named ignimbrite reaps little rewards. An incredibly weathered outcrop is what we discover and this is impossible to sample usefully. We have, however, tested our fitness by climbing down pretty much a vertical slope, zig-zagging all the way. Thank heavens the high altitude grasses or Sacaton are strong rooted or this reporter would be no longer with you. We stop, eat chocolate and ponder our route to meet up with Hugo.

Our first evidence of large mammals as we hike our way to meet Hugo.

The compass looks right, the road looks semi-alright (in two places we duck under barbed wire to continue) and we feel confident of our direction to the jeep. An hour passes and Chiara seems slower and more laboured. We check on her health and she admits to feeling the altitude as she takes out her inhaler and calms her asthma. Dave and I have headaches. Unusual and intense.

We continue more slowly and Chiara hangs back to throw up in the most polite way I have ever seen. There's no doubt it's moderate altitude sickness. A few more stops and Hugo hoves into view. Exhausted glee. It's back to base and straight to bed after a long day in the field.