exactly long before. “I’d suggest there can’t be any danger farther than, say, three times the river’s width away from the cliff foot. When they get that far, maybe they could put the set down occasionally to give us a steadier look and better pictures.”
“Maybe. But leave that decision to Dondragmer.”
“Of course. But you still have two cameras besides that one; maybe he could leave it—”
“We’ve been using all three. Dondragmer decides. I know what I’d do with my present knowledge, but he’s there.”
“All right.” There were beings, most of them non-human, on Toorey who might have argued further, but Jeanette Parkos was not one of them. She was very conscious of who was in charge on the surface, and as chief communicator realized clearly who would be blamed if any major disagreement should develop with the Mesklinites. “We’ll report to you as well as we can when the collapse gets in sight from where Dondragmer is, if it does.”
“Good. I’m still hoping it won’t. That other one we climbed to get up here—”
“The other one is much narrower than this one is already. Whatever caused it can’t have been as energetic.” Another alien voice cut in. “That’s silly! Practically all the energy involved now is coming from falling rock. You have a chain reaction.”
“But that must have been true for the other fall, too!” Barlennan turned his attention back to the still spreading collapse. He had learned long ago the futility of listening to Flyers arguing theoretical points when anything was actually going on. They got too far behind real time much too quickly. No doubt it was because they were too far away to feel personally involved. The captain was not; he turned his eyes back to the explosion site. At least, nothing more was flying through the air. Their own climb had ceased, according to the tracker and his own eyes; the balloon had reached its ceiling, which was low because of the rapid decrease of air density with altitude. Hars’ efforts were now focused on keeping its height constant; altitude control was highly unstable. Even a slight dip caused a decrease in balloon volume, and hence a decrease in lift, which tended to make the dip deeper. It was like the hollow boat’s behavior, so many gravities to the north. Hars had developed a high skill at handling this problem; it had been he who had conceived the deflectors which gave quick control over how much hot air was actually entering the bag, and eliminated much of the control lag involved in merely feeding fuel or sprinkling meat juice on the fire. “It’s coming.” The human voice sounded less excited than the captain felt was appropriate, but Jeanette was not, of course, in danger herself. One should make allowances. “How close?”
“It’s just come around the point about three miles upstream.”
“How far is the debris spreading out into the river?”
“I can’t tell very well yet. The set is on the ground, or as near as no matter. The edge view I get for the bend seems to show repose at about forty degrees for the stuff near the top, and maybe twenty near the bottom. That would mean anything that?s more than about one cliff height away from the original bottom should be safe.? “That does not quite include the ship,” Barlennan pointed out. Dondragmer cut in. “There wouldn’t be time to get back to the ship, much less to tow it overland any distance, before the fall gets here.”
“All right. Make sure the crew is safe. Head for the site where this balloon was built; that has to be safe, and a lot of our stuff is there anyway.”
“Yes, Captain. We’ll start searching for ship building materials at once, when we get there. Have you further orders?”
“None for now, except when you think you’re far enough out to be safe you should set the Flyers’ eye where they can see what happens. Remember they can see things over again, and could be able to tell us how best to find and recover anything that gets buried.” Dondragmer was probably the least susceptible of the Bree’s crew to being startled, and had spent many thousands of days burying and then digging out the alien rocket, but the thought of excavating a rockfall jolted him. Several of the crew could tell this. None, however, said anything, and the communicator was set down and pointed as the captain had ordered. The natives stayed where they were afterward, and nervously watched the collapse region as it neared them. They could see that the falling material was pretty certain not to reach them, but Mesklinites in general are not calm about anything’s falling. Not even Mesklinites with the background of Barlennan’s crew. The roar of the rocks was loud enough now to drown out even their voices, and there was no conversation as the wave thundered past in front of them. From Toorey, the view through the lens involved less emotion, though several of the watchers were already, and everyone hoped prematurely, wondering what the loss of the original Bree would do to their plans. More were observing, in as much detail as the optics allowed, the way new vertical joints appeared closer and closer to the watchers, delimiting sections of rock which began to tilt slowly outward — a slow fall was a phenomenon on Mesklin — and then develop horizontal cracks which shot back toward the areas already bared by the downward disappearance of previously loosened material. The rock above each crack tilted slightly outward and vanished in its turn, reappearing as it shattered on the growing slope below. Lower segments of the falling prisms were just as invisible during their falls, but didn’t fragment as completely before coming to rest. The repose angle grew steeper as the eye traveled upward and encountered less and less fine material and more and more large slabs and columns. On any other world the details would have been mostly hidden by dust — with or without an atmosphere to suspend it. Not on this one. The collapse wave thundered past. Dondragmer retained enough presence of mind to turn the vision set to the left, so the Flyers could keep watching its progress. This was just as well, because it let them see its sudden halt. The wave was fully two miles past by this time; whatever stopped its progress could not have helped the ship still on the river bank. But it did stop. Within seconds, the debris seemed to have reached equilibrium. The observers, local and offworld, found themselves looking at a new straight-up cliff far to their left extending inward from the former face, roughly toward the grounded rocket. Its lower section was partly hidden by the scree slope so suddenly formed, but what could be seen was as nearly vertical as the original had been. Several of the Mesklinites, rendered more nearly insane than their fellows by the events of the last thousands of days, promptly started back toward the cliff, slanting downstream to get a look at the end of the fall. Dondragmer was equally curious but ordered them back. Jeanette interrupted his commands. “It’s probably safe enough, Don. The stuff must have reached repose angle right away.”
“No doubt you are right, Flyer Jeanette, but we will first bring the captain up to date with events. He could not have seen this, unless the balloon has moved remarkably fast in the right direction. You would know better, but I can’t see it from here. Also, you do not mention that the repose angle, if it really is that, is much steeper for the higher, larger fragments than for the much finer material near the bottom.”
“You know,” cut in another alien voice, “this will be the first chance we’ve ever had to get a close look at the rock making up that cliff. We could see it was sedimentary, if horizontal layering means anything, but all we could tell was that the bottom fifty feet or so was light gray in color, the next layer up was a lot darker, and for the rest of the way up there were variously light and dark bands up to the nearly black one at the top. That one’s silicate — mostly amphibole, the gear on the rocket told us years ago right after the landing, but this will be the first time we’ll be able to tell anything about the other layers.”
“What will we be able to tell?” snapped another. “Just what will color tell us, and what else will we be able to see?” Dondragmer, like the captain, tuned out the argument. He had more important problems to face. There was no more visible rock motion anywhere along the fall; the stuff must, indeed, have reached some sort of equilibrium. There was no more sound even from the left, where falling material must presumably have taken a little longer to fill space around the new corner. But something — the “smoke” described a little while before? well, maybe ordinary fog — was rising from the far side of the river, over the newly fallen material. Even after watching balloons, the sight of something flowing upward was startling. Explanation would have to wait, though. There were fragments of all shades and several colors at the bottom of the fall, but the mate was more concerned with what might be under it. What had happened to the Bree? And for that matter, what might have happened to the river? He didn’t worry about the captain, who had presumably been almost as much out of danger as the Flyers. After a few moments’ thought, he headed toward where the ship had been, ordering a few of the crew to come with him carrying the communicator, and sending off others to examine the edge of the fall both up and down stream. Almost immediately he had a question to ask the aliens above. “It’s getting a lot warmer as we get near the fallen stuff. Can you suggest why?” Even Jeanette could, but one of the scientists undertook the explanation. Not even Dondragmer had really grasped much thermodynamics yet, but many of the natives had a fairly clear idea of energy. Every falling pebble had lost a lot of potential— Quite a lot. More than enough, for the
