For decades, daredevils and adventurers had explored the New Lengai Fissure Zone and all its wonder. From above, it didn’t look all that threatening. Magnificent, to be sure, but not scary. As the monocopter descended I could make out the distinctive white terraces, like scales down the flank of the mountain, directing black flows that stretched for kilometres.

My pilot and I knew what we were really looking at. The flows were not of water, but of carbon-rich lava that ran continuously from volcanic vents. This was very unusual lava because it ran like water, even becoming turbulent in a few confined spots. Time and exposure to the air eventually chilled the lava into a thick, brown slush, then into the soft, white rocks of the terraces.

Amazing though it was, we weren’t there to film the black stream itself. We were more interested in the person surfing on top of it; the undisputed queen of lavaboarding, Sika.

“We’re coming in for landing,” crackled the pilot’s voice. “Your camera crew is already down and setting up, Doctor.”

“Spiffing,” I replied. My AR glove was already in communication mode, so I waggled my fingers to tell the crew they could start as soon as they were ready. I didn’t need to be there for this sequence. In truth, I only wanted to see Sika in action, or I would have flown straight to the cave system at the base of the volcano. That was where the real story was.

Our monocopter touched down, slowed its rotary stabilisers and folded away its rotor. We stepped out onto one of those awesome terraces, its circular form some thirty metres in diameter. I strode right up to the edge, scope in hand. Under a perfectly clear sky, I could make out every detail of the hot, black torrent below us. It bubbled, sizzled and popped; the sound of meat being roasted. There was certainly an ambient heat, nowhere near as strong as I’d felt on the basaltic islands of the Neotethys, but enough to make my biological parts sweat.

“Over there, Doctor,” the pilot pointed. Sure enough, my trusty cameraman and soundwoman were finishing their equipment checks on a platform below us. Several film drones hovered around them. “Best I lead the way. This part looks like it might crumble at any moment. Do you have everything you need?”

I said that I did, but wished I’d brought some chocolate, as the brown half-solid lava reminded me of its lumpy texture. We clambered along and down, kicking clods of carbonatite loose as we went. The displaced stones disintegrated as they clattered down the slope, their fragments plopping quietly into the lava. My cameraman, as it turned out, was already rolling. I stared excitedly. Sika was incoming.

She appeared in a flurry of black globs that chilled to brown in mid-air. Her protective pyrosuit shone like fire under the sun. Like her stout lavaboard, it had the striking purple colour of a sliced whiskerbean. Down the terraces she swooshed, flinging up 500-degree waves that washed harmlessly across her body. Her legs and torso twisted constantly to keep her upright, her arms stretched horizontally to provide balance.

Sika’s gaze was not fixed on her board or on the drones hovering around her. She kept her eyes firmly on her destination; the caves straight ahead. Her behelmed head was remarkably still, as if a giant were holding onto it, but letting the rest of her worm around underneath. Years and years of practice showed in her graceful movements, her extraordinary focus and the way she slid effortlessly across the surface.

Our cameras worked hard to keep up as she surfed the river of lava. One drone smacked into a rocky shelf as she passed by us. It fell and disappeared into the bubbling blackness, but none of us would fret. Drones were cheaper than chairs back in the city.

Our subject finished her display with a stunning ramp, flipping her board as she rose above the rocks. She flew away from us, all the way into the cave mouth where faint green and blue lights blinked in the darkness. Her cybernetic legs absorbed the shock of her landing, engaging with a hiss that echoed back out into the open. Behind her, the lava was swallowed up by a crevasse that amplified the sizzling sounds within. We had our opening sequence.

“Spiffing!” I said. Our journey to the cave was rather less graceful. The four of us gathered up the equipment that didn’t fly and climbed down to join Sika. We eventually reached her and walked deeper into the cave to get away from the now-deafening torrent. It was very warm inside, but also humid, perhaps from groundwater evaporated by the heat of the volcano.

Sika was grinning when she removed her pyrohelmet to reveal a tangle of curled, silvery hair. She bumped our fists in turn – the traditional lavaboarder’s greeting. Then she looked up at the blinking lights of the film drone and asked, “Is that one still recording?”

“It’s live-streaming,” replied the soundwoman. “We broadcast live on both our network’s science channels: Nature’s Wonder and Parole d’Explorateur.”

“Oh. Hello, world!” Sika waved and gave the drone a shy smile. I’d later learn that no less than a million were watching her.

Our chatter was brief, for we were anxious to film the main piece. New Lengai’s caves had been considered a natural wonder for generations, but it was only recently that their true significance was discovered. The cave systems were formed over thousands of years by the interactions of the black carbonatite lava flowing from above with a tholetiic mantle plume from below. They had produced a geological system that extended for dozens of miles and was revered and worshipped by Sika’s people.

The faint lights we’d seen twinkling earlier became much more prominent as we penetrated further into the cave system. On all sides, the swirling, faulted, greyscale walls were studded with lights: green, blue, red, white and combinations of all four. They were crystals ranging from fingernail-sized to the width of Sika’s lavaboard. My crew and I gasped. We’d seen the newsclips, of course, but they failed to do the real thing justice.

“Welcome,” said Sika, “inside the Crystal Brain.”

There was no need for lampsticks in the chamber where we had stopped. Clusters of plagioclase, forsterite, calcite and other silicates shone from all angles. Yes, this was the incredible Crystal Brain, a network of crystalline neurons that, in the heat from the lava beneath, could transfer information as ions through three solid solutions. It was not alive in any sense humans would understand, but there was undoubtedly a kind of life there. As we watched, minerals connected to the carbonate solution twinkled and blipped, and the flow of calcium and sodium in the plagioclase solution turned the blue ones a rusty reddish.

“My elders have shown me how to talk with it,” Sika continued. “Would you like to see?”

I said that I would, and ensured every camera at our disposal was rolling. We were led over to a cluster of prismatic carbonate crystals that protruded from the sloped floor and reached up to hip height. Sika kneeled before them, then detached her gloves and placed a smooth hand on the tallest of the crystals. Her expression was serene and relaxed, but the rest of us knew what she was doing required intense concentration. It would take a moment for her biochemical brain to interface with the geochemical one.

We got the response a minute later. A screen of bluish feldspars shone out from the darkness above Sika’s head, illuminated by a rush of excited ions. I had to shield my eyes as the light grew brighter than the summer sky, dotted with the white points of the crystals projecting it. Then another chemical change created a layer of green, then a smear of white and black materialised, and I realised we really were looking at the sky, but also the fissure zone and the river of lava we had just left behind. It was a hazy, shimmering image of the tropical world above us.

Sika stood up and wiped her hand on her pyrosuit. It was shining with sweat. “I’m sure you know the Brain is self-aware. It has already passed the classic tests that most human-made artificial intelligences fail. Its computational power is… astronomical. Possibly, even greater than that of our own brains.” She smiled at me. “And you’re the first natural historian to record it for the whole world to marvel at. How wonderful!”

My eyes were still drawn to the image on the wall, blinding though it was, so I just said, “Spiffing.” Caught up in the wonder of it all, I’d nearly forgotten we were there to make a documentary. However, it was time to get to work. Sika was just our guide; I was the one who had to talk into a camera and provide perspective. I nudged my cameraman and my soundwoman, who were similarly transfixed by the feldspar screen. So was my pilot, but he was harmless enough where he stood.

When we were ready to begin, I asked Sika if she wanted to say anything before we switched to the junior-friendly script. She nodded and told me, in a quiet and careful voice, “The people of New Lengai approve of your goals here, but they wanted me to give you and your audience a reminder. The Crystal Brain is, in our view, a living being. It feeds on the magma that wells up underground and gives energy back to the world as light. It grows as the volcano grows and it should live for as long as the lava flows through it.”

“But if the volcano were to die, so would the Brain. I know it seems silly to consider, but the Australochine Federation have machines that could do it. What I meant to say is… there is so much we don’t yet understand about the world and so much potential for destruction if we make the wrong choice. I hope your viewers will continue to make the right choice and protect the ecosystems you explore, Professor.”

I said that I would make a point of it in my film. With that, we got to business. Our network ratings were going to be spectacular.