Subterrestrial by Michael McBride

Halversen’s team had done a miraculous job of keeping a lid on the TransBering disaster so far, but at the rate the water was returning and the seas were rising, they wouldn’t be able to contain it forever. The Halversen contingent couldn’t allow that to happen, at least not until they had a grasp on the one variable for which they couldn’t seem to account.
    The entire leeward side of the island was slick with a foot-thick layer of ice formed where the heat rising from the mouth of the stone orifice melted the snow. The chunks of granite and ice that once sealed it formed a treacherous slope over which Martin and his men had been forced to use crampons and ice axes to climb.
    Martin cast one final glance at the sky and ducked inside the cave. His men followed without prompting. Paul Sullivan and Oleg Renton, who’d been with him since Afghanistan, knew him well enough by now to read his moods. Besides, they were smart men who recognized what was required of them and when.
    The screaming wind faded behind him as he descended into a zone of utter silence. It reminded him of wearing earplugs. His own breathing was amplified tenfold and his heart beat so loudly it nearly had an echo of its own. The walls were cold and gray and so narrow that he felt constricted, as though he were crawling down the throat of some monstrous being. He heard the hollow plinking sound of condensation dripping from somewhere ahead of him and felt the faint vibrations in the stone from water flowing beneath him. While they’d worn their Thermoprene wetsuits for just that contingency, he really hoped they weren’t going to need them. Their mission was one of simple reconnaissance: they were to survey the subterranean passages detected by thermal satellite imaging and plant the fail-safes at a point where their detonation would collapse the tunnels. The last thing they could afford was for whatever had surfaced on Little Diomede to reach the mainland, assuming it hadn’t been eradicated in the explosion that rained liquid fire and tons of debris down the air vent. What kind of idiots stored hundreds of thousands of gallons of highly combustible fuel on an island within shouting distance of the most seismically unstable region on the planet anyway? They were just begging for a major catastrophe.
    The roof of the cavern lowered as the ground sloped downward. The granite gave way to gneiss and migmatite that sparkled in the beams of their headlamps. The sedimentary layers grew closer together until they fused into sandstone, which abruptly gave way to limestone and jagged karst topography. His light reflected off the placid water maybe ten feet down, where the tunnel vanished beneath it. The subterranean river was still some distance beneath them, flowing high and fast and shunting the overflow into the caverns above it, flooding the warrens with a combination of freshwater and brine that he couldn’t help but equate to bilge water.
    He stepped into the cold water and carefully felt his way down the decline. There was maybe two feet of air above the water level, just enough for him to keep out his head and upper chest. He couldn’t quite stand erect, but it was vastly preferable to having to swim. The feel of terra firma under his feet gave him some semblance of control over the situation. After all, he’d been a Ranger, not a SEAL.
    Droplets of condensation streaked across his peripheral vision at the very edge of his light. The surface rippled from his exertions and refracted his light onto the stalactites and the earthen roof. His men’s lights swept the cavern from one side to the other. Its dimensions were impossible to divine thanks to the darkness and the flooding. The lack of current caused the sediment to float around them in a murky brown cloud and settle to the ground in a layer so slick that maintaining his traction became a conscious act of defiance.
    Renton slipped and went under with a splash. He emerged with a startled gasp