Convergent Series by Charles Sheffield

preparing to endure the higher temperatures that went with Summertide.
    Before Rebka could say anything, Perry was staring all around and shaking hishead.
    "I don't know what's going on here." His face was puzzled. "I said we'd find trouble, and I wasn't joking. It's too damned quiet. And we're less than thirty days from Summertide, the biggest one ever."
    Rebka shrugged. If Perry were playing some deep game, Rebka could not see through it. "Everything looks fine to me."
    "It does. And that's what's wrong." Perry waved an arm, to take in all the scene around them. "It shouldn't be like this. I've been here before at this time of year, many times. We should be seeing quakes and eruptions by now—big ones. We should feel them, under our feet. There should be ten times as much dust in the air." He sounded genuinely confused.
    Rebka nodded, then turned slowly through a full three hundred and sixty degrees, taking plenty of time for a thorough inspection of their surroundings.
    Right in front of them stood the broad foot of the Umbilical. It touched the surface, but it was not held by a mechanical tether. The coupling was performed electromagnetically, field-bound to Quake's metal-rich mantle. Perry had told him that it was necessary because of the instability of the planetary surface near Summertide. That was plausible, and consistent with Perry's claim about the violence of the event. Why else would the Builders have avoided a real tether? But mere plausibility did not make the statement true.
    Beyond the Umbilical, in the dirrection of Mandel's setting disk, stood a brooding range of low mountains, purple-gray in the dusty air. The peaks were uniform in size and strangely regular in their spacing. From their harsh profile and the steep angle of their ascent, they had to be volcanic. But he could see no pall of smoke standing above them, nor any evidence of recent lava flows. He looked closer. The ground beneath his feet was smooth and fissure-free, with no gaps in plant growth to testify to recent fracturing of the surface.
    So this was Quake, the great and terrible? Rebka had slept easy in environments ten times as threatening. Without a word he began walking toward the lake.
    Perry hurried after him. "Where are you going?" He was nervous, and it was not simulated tension.
    "I want to have a look at those animals. If it's safe to do it."
    "It should be. But let me go first." Perry's voice was agitated as he moved on in front. "I know the terrain."
    Nice and thoughtful of you, Rebka thought. Except that I don't see a thing in the terrain that needs knowing. The ground was marked here and there by patches of igneous outcrops and broken basaltic rubble, a sure sign of old volcanic activity, and the footing was sometimes difficult and uneven. But Rebka would have no more trouble traveling across it than Perry.
    As they moved toward the water the going actually became easier. Closer to the lake lay a sward of springy dark-green ground cover that had managed to find purchase on the dry rocks. Small animals, all invertebrates, scuttled to hide away in it from the approaching strangers. The herbivores held their ground until the two men were a few meters away, then unhurriedly sidled off toward the lake. They were round-backed creatures with radial symmetry, multilegged and with cropping mouths set all around their periphery.
    "You know what's bugging me, don't you?" Rebka asked suddenly.
    Perry shook his head.
    "All this." Rebka gestured at the plant and animal life around them. "You insist that humans mustn't come to Quake too near to Summertide. You say we can't survive here, and I'm supposed to tell Julius Graves and the others that they are not allowed to visit, and we'll lose the revenue they'd generate for Dobelle. But they stay here." He pointed to the animals making their slow way to the water's edge. "They survive, apparently with no trouble. What can they do that we can't do?"
    "Two things." They had reached the lakeside,