Convergent Series by Charles Sheffield Page B

curiously orderly, their spreading darkness bursting precisely from every third peak. He gave one quick look the other way—would water be a safer haven?—and then followed Perry. The ground began to shake, to seesaw back and forth so that he was close to losing his balance. He felt he had to slow down, until a mass of glowing ejecta, a semimolten rock the size of an aircar, plummeted in and lay sizzling within twenty meters of him.
    Perry was already in the capsule at the foot of the Umbilical, holding the lower entry port wide open.
    Rebka hurled himself throughit headfirst, sacrificing dignity for speed. "All right. I'm in. Move it!"
    Perry ran madly up the stairs to the control-and-observation chamber, and the car was starting into upward motion before Rebka had picked himself up and checked for injuries. Instead of securing the hatch and following Perry, he turned to the entry port and left it open a foot or so. He peered out.
    Whistling lumps of rock and lava continued to pelt the area they had left. He could see fires as the ejecta seared the brush and the dry ground, and hear occasional fragments smacking into the Umbilical above and below them. They would do no damage, unless one entered the open port. He would have time enough to see it coming and to slam the door closed.
    The most vulnerable items were the imported aircars. They sat in a neat line at the foot of the Umbilical, built by humans and brought from Opal for local exploration and use. As Rebka watched, a smoking chunk of rock hurtled toward the top of one of them. When itbounced away without makingcontact, he realized that the cars were sitting beneath a protective sheet of transparent Builder material—cannibalized, probably, from part of Midway Station.
    He looked to the horizon. From their present height of two or three hundred meters he could see a long way through Quake's murky air. The surface was aflame with small flash fires, all the way to the distant peaks. Rising smoke brought a pungentaroma to his nostrils, resinous andaromatic, and the ground below was shimmering withheat andblurred by dust.
    It was clear that the source of the disturbance was restricted to the single line of volcanoes that lay between them and Mandel's glowing face, low to the west. Every third peak carried a dusky plume and a pall of smoke above it. But already the force of the eruption was dwindling. The smoke clouds were no longer shot through with crimson and orange, and fewer rocks came sailing through the air toward the car. The herbivores had disappeared long ago, presumably hiding in the protective depths of the lake. They would know when to come out again.
    Perry had left the controls and was crouched at Rebka's side. The car's movement up the Umbilical had ceased.
    "All right." Rebka prepared to close the port. "I'm persuaded. I wouldn't want to take the responsibility for allowingpeople here at Summertide. Let's get out of here and head back to Opal."
    But Perry was holding the door open and shaking hishead. "I'd like to go back down."
    "Why? Do you want to get killed?"
    "Of course not. I want to take a good look at what's happening, and really understand it."
    "Quake is approaching Summertide, Commander. That's what's happening. The volcanoes and earthquakes are starting, just the way you said they would."
    "No. They're not." Perry was more contemplative than alarrned. "There's amystery here.Remember, I've been on Quake before at this time of year, many times. What we just saw is nothing, just a little local fireworks. We should have found more activity than we did,one hell of a lot more.The surface was quiet when we arrived;it should have been shaking all the time. And the eruptions looked impressive, but the ground tremors were nothing. You saw howquickly they died away." He gestured out of the port. "Look at it now, everything becoming quiet again."
    "I'm no planetary geologist, but that's just what you would expect." Rebka could not understand what was