The ice mass on the eastern side of the remaining dorsum was at one point very near to the ridgeline. The dirigible captain let out more anchor line and they floated east on the prevailing wind until they were directly over the ridge, where they could see clearly that only meters of rock remained to be overcome. And off to the east was a walking pipeline, a blue hose sliding slowly back and forth on its ski pylons as its nozzle shot water onto the surface. Under the drone of the props, they could hear occasional creaks and moans from below, a muffled boom, a high crack like a gunshot. There was liquid water below the ice, Diana explained, and the weight of new water on top was causing some sections of ice to scrape over barely submerged dorsa. The captain pointed to the south, and Maya saw a line of icebergs fly into the air as if propelled by explosives, arcing in various directions and falling back onto the ice, breaking into thousands of pieces. “Maybe we’d better back off a little,” the captain said. “It would be better for my reputation if we did not get shot out of the sky by an iceberg.”

The walking pipeline’s nozzle was pointing their way. And then, with a faint seismic roar, the last complete ridge was overwhelmed. A rush of dark water ran up the rock, and then poured down the western side of the ridge in a waterfall some hundred meters wide. It fell the two hundred meters of its descent in a slow lazy sheet. In the context of the great ice world stretching to the horizon in every direction, it was no more than a trickle— but it kept pouring steadily, the water on the eastern mass now channelized by ice on its sides, the falls booming like thunder, the water on the western side fanning out in a hundred streams through the broken ice— and the hair on Maya’s neck lifted in fear. Probably a memory of the Marineris flood, she decided, but couldn’t say for sure.

Slowly the volume of the waterfall decreased, and in less than an hour it had all slowed and then frozen, at least on the surface; though a sunny fall day, it was eighteen degrees below freezing down there, and a line of ragged cumulonimbus clouds was approaching from the west, indicating a cold front. So the waterfall eventually stilled. But left behind was a fresh icefall, coating the rock ridge with a thousand smooth white tubes. So now the ridge had become two promontories which did not quite meet, like all the other ridges of the Zea Dorsa, all diving into the ice like sets of matching ribs: matching peninsulas. The Hellas Sea was continuous now, and Minus One truly an island.

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