He surged forward and veered into the main tunnel facing the entrance to the magma chamber, where Costas should have been visible. What he saw instead was an image from hell. A surge of lava was lapping towards him, five metres or more into the tunnel. All his instincts told him to go back, to seek some other way out, but he knew he had to go forward and swim over the lava to where he could now see Costas’ beam shining at him no more than ten metres away.
He finned frantically, following the tethering line for the ROV. After five kicks he was over the lava, almost within touching distance. He was being pushed against the roof of the tunnel, and realized to his horror that the boiling water above the lava was rising and forcing him upwards. He remembered his failing coolant system. He was beginning to overheat. The sweat dripped off his face on to the interior of his visor, and he could see the outside of his suit crinkling and turning brown. He was being cooked alive. Suddenly there was a yank on the tether line and he held on, feeling himself being pulled. He turned upside down and clawed his way along the ceiling, but then remembered his cylinder and air pack. He might survive the Kevlar on the front of his suit being scorched, but not his breathing gear. He turned over again, drew himself up into an upside-down crab crouch and pushed his feet and elbows against the rock, hopping forward a metre or so each time, trying to keep his helmet away from the lava. The sweat in the inside of his visor began to boil like spatters of water on an oven hot ring. He pushed one last time and was free, rocketing up into Costas in a tangle with the tethering line. He was dimly aware of Costas unhooking the line and fumbling with his wrist control panel, and he saw that the thermostat had been turned down to its lowest setting, ten degrees Celsius. Costas spun him round and stared him in the face. ‘There may be enough juice in that thing to give you a burst of cool air before it packs up. Can you feel it?’
Jack felt the sweat drip into the corners of his mouth, and then he sensed the coolness. He opened his eyes, blinking the salt out, then reached with his lips for the water tube and sucked hard, grateful that he had not tried to come out upside down and cooked the water reservoir on his back. He spat out the mouthpiece after a few gulps, then gasped hard for a few moments while Costas looked him over. ‘I don’t see any sign of leakage in your e-suit. But the heat-resistant outer shell and the Kevlar is melted from your elbows and knees. You’re not going anywhere near lava again and surviving it. Which is a good thing, because as of about a minute ago, that option closed on us anyway.’
‘What option?’ Jack gasped. ‘What do you mean?’
‘I mean the option of going back the way we came. The option that would have taken us close to the lava again. Take a look.’
Jack floated free of Costas, kicking a loop of the tether cable away, then looked down. It was a terrifying sight. The lava below them had risen at least five metres in the time since they had exited the tunnel. He suddenly realized what Costas meant. He looked over to the tunnel entrance, where the borer had broken through into the magma chamber, their entry point. A great surge of lava flowed up into it, and then another. He spun around to Costas. ‘What are the options?’
‘When Lanowski and I took the submersible over the volcano, we saw a number of places where gas was escaping into the sea. Mostly they were pinpricks, but there was one really big flow. I took a GPS fix on it and I’ve just been trying to relate that to all the directional data I’ve got from our dive. I think it’s one of those two caverns above us.’
Jack looked directly up, and saw two distinct areas of blackness in the rocky ceiling of the chamber some ten metres overhead. ‘Which one?’
‘We’ll have to take pot luck.’
There was a heave in the water, and Jack looked down. To his horror he saw that the entire lava lake had surged upwards, and a great bulge like a wave was rippling towards them from the far side of the chamber. ‘Up! Now!’ he shouted. He finned hard, remembering to breathe out as he did so, then stopped and flipped round, heading back down. Costas was struggling with the tether cord, which was caught around the strap of one fin. Jack reached behind his breathing pack, whipped out his knife and pulled the serrated edge as hard as he could against the cord, sawing the knife against the metallic cable inside. The cord snapped and he pulled Costas’ foot away, smearing himself with the melting rubber of Costas’ fin. He finned frantically upwards, grabbed the cord at the back of Costas’ pack and yanked it to fill the emergency flotation wings in the shoulders of the e-suit. He exhaled forcefully to avoid an embolism and prayed that Costas was doing the same. The lava surge passed only a few metres below them, and seconds later they hit the ceiling of the chamber, jarring against the lava. Jack still had his knife in his hand, and he stabbed it into Costas’ buoyancy aid to expel the air, watching as the bubbles from the torn fabric disappeared up into the darkness above. Costas pushed off, looking down at the melted remains of his fin, and then at Jack. ‘Phew. That was close.’
Jack felt himself close to boiling point again. He took a slurp of his water, now unpleasantly warm, and looked down. The lava was surging up all round them, rising at a horrifying speed. ‘I think what we’ve got here is a major volcanic event,’ he said hoarsely.
‘No kidding. It’s called an eruption. And with the lava pressing up into this space, the volume of water inside the chamber is decreasing and boiling up. There’ll be a flashpoint and another phreatic explosion and everything will vaporize, including us.’
A lava fountain licked the bottom of the divide between the two caverns. ‘See that?’ Jack said. ‘We haven’t got any choice. It’s going to have to be this cavern.’ He pushed off the wall, and they both began swimming up. Jack glanced at his gauge. They were sixty-five metres below sea level, which put them about ten metres higher than the point on the outside of the volcano where they had left the sub. He looked at Costas. ‘Does that magic program of yours tell us how far away the sub is?’
‘The system’s crashed in the heat. But I think we’ve come in a curve, so not as far as we’ve swum. Maybe fifty metres from here, a bit more.’ They reached the top of the chamber, a jagged ceiling of solidified lava that looked like malformed stalactites, with deep cracks and crevices between. The upper recess was about five metres wide. Costas flicked on both of his headlamp beams and swam a circuit on his back, staring up, before returning to Jack’s position. ‘There are three possibilities. How much air have you got?’
‘Almost on reserve. Fifty-five bar.’
‘Okay. You vent carbon dioxide from your rebreather into one chamber, I’ll do mine in another. You’ve got about ten bar more than me left in your breathing gas, so for the third chamber vent some air straight from your tanks.’
‘Roger that.’ Jack followed Costas to the first hole and pressed the button that vented the accumulated carbon dioxide from his rebreather. They watched the bubbles ascend in the beam of Costas’ headlamps, and Costas peered hard while Jack looked down at the lava surging below them. ‘I can see where the gas is pooling against the ceiling,’ Costas said. ‘Nothing’s escaping.’ They moved to the next spot and repeated the process. An arc of lava shot up in the water to within a few metres of them. Costas looked at Jack. ‘Same story.’
‘You sure?’
‘Yep.’
‘This is it, then.’ They looked at each other, then peered down. Jack realized that the lava was rising with greater speed now because the cavern had narrowed, forcing the molten material upwards. ‘We’ve just run out of time.’ An upwelling of gas enveloped them and they both caught hold of a lava protusion just in time to prevent themselves from falling. They finned together up the last five metres, face to face, until they hit the ceiling. Jack saw something, twisted sideways and switched off his headlamp. It was a patch of green light coming down around a hanging pillar of lava about five metres away. He pulled his way over and peered at it, then looked upwards, his heart pounding. They might make it. He had a sudden thought, and turned to Costas. ‘You got any detonator cord?’