shirking inability to confront her, even if it did arise from some kind of consideration for her. And the way he stayed always busy at his screen—he never actually looked out the low floor windows of the rover, to see the flood with his own eyes. The cameras have a better view, he would say mildly when Michel urged him to have a look. And after only a half hour of watching the first arrival of the flood on the TVs, he had gone to his AI screen to work out what it might mean to his project. Water rushing down Ius, freezing, breaking up and rushing down again; certainly into Melas; whether there would be enough water to make it into Corprates, and then down into Capri and Eos, and then down into the Aureum Chaos … it seemed unlikely on the face of it, but the Compton Aquifer had been big, one of the biggest ever found. Marineris very likely owed its existence to outbreaks from earlier incarnations of the same aquifer, and the Tharsis Bulge had never stopped outgassing…. She found she was lying on the floor of the rover, watching the flood, trying to comprehend it. She tried to calculate its flow in her head, just as a way to focus better on what she saw, to bring it back out of the meaninglessness that threatened to overwhelm her. Despite herself she felt the fascination of the calculation, and of the view, and even of the flood itself; this had happened on Mars before, billions of years ago, and probably just like this. There were signs of catastrophic floods all over, beach terraces, lemniscate islands, channel beds, scablands…. And the old broken aquifers had refilled, from the Tharsis upwelling and all the heat and outgassing that that engendered. It would have been slow, but give it two billion years….
She forced herself to focus, to see. The near edge of the flood was about a kilometer away, and 200 meters below them. The foot of the northern wall of Ius was about fifteen kilometers away, and the flood stretched right to it. The flood was perhaps ten meters deep, judging by the giant boulders that rolled downstream like Big Man’s bowling balls, smashing ice to shards and leaving steaming black polynyaps in their wake. The water in the open patches seemed to be moving at perhaps thirty kilometers an hour. So (punching figures into her wristpad) perhaps four-and-a-half-million cubic meters per hour. That was about a hundred Amazons out there, but running irregularly, freezing and bursting in a perpetual series of ice dams building and failing, whole steaming lakes leaping downhill over whatever channel or slope they found themselves on, stripping the land down to bedrock and then tearing the bedrock away…. Lying on the floor of the rover, Ann could feel that assault in her cheekbones, vibrating the ground in a rapid pounding. Such tremors hadn’t been felt on Mars in millions of years, which explained something else that she had seen but not been able to comprehend; the northern wall of Ius was moving. The rock of the cliffs was flaking off and falling into the canyon, which shook the ground, and triggered more collapses, and giant waves that washed out into the flood, water pouring back upstream over the ice, the rock bursting apart in explosions of hydration, the frost steam pouring so thickly into the dust-choked air that she could see the northern wall only in snatches.
And without a doubt the southern wall would be collapsing in a similar way, although their view of this wall, which loomed over their road to the right, was foreshortened and cut off. But it had to be falling. And if it flaked off above them, then they were dead for sure. It was quite possible—very possible. Judging by her glimpses of the north wall, the chances might be as high as 50 percent. But then it was probably worse over there; the northern wall appeared to be undercut by the flood, while the south wall was removed from it by the bench they were driving over. So the southern cliffs should be a bit more stable—
But then something drew her eye forward, downstream from them. Up there the south wall was indeed collapsing, falling in great sheets of rock. The base of the cliff exploded in a cloud of dust that bloomed over the talus, and the upper sections of the cliff slid down into this