Hal Clement - Heavy Planet

“Hmph. He hasn’t gotten very far. I’m reminded of an animal on my own world which traps its prey in pits rather like this — loose stuff at its angle of repose. Climbing such a surface is nearly impossible. What will he do if he gets to the top? That hole is twenty of your body lengths away from the bank.”

“But, Doctor!” pointed out Estnerdole, “the stone itself is not very thick. If we can reach the top, we know the stone comes to an end only a short distance to the south. We can dig our way out from under the edge easily enough.”

“True enough. All right, the rest of you might as well try climbing too. So, for that matter, might I; if I get out on the surface I can call for help instead of having to send a runner.”

“Rest first,” advised Destigmet. “You can’t be in very good condition yet. You must have been hurt some, if the state of your face plate means anything.”

“All right. I want to think, anyway.” Near-silence fell while the rest of the students began to climb. Two or three, starting just below the stranded tank, had little trouble getting as far as the vehicle; but from there on it was a different matter. The creatures were tiny, some fifteen inches long with split-cylinder bodies an inch and a half in diameter. They were light; their half-pound masses weighed less than a kilogram at Mesklin’s equator. Even that weight, however, sank their tiny legs full-length into the snow. The motion of the short limbs could be inferred from the clouds of white dust which sprayed backward from the small bodies. A hollow formed around each slender form, with material sifting down into it from the front and sides. Behind, it built up into something approaching a level surface, and slowly — very slowly — the Mesklinites followed their fellow uphill. Sometimes one would speed up briefly as he encountered a slightly more firmly packed area; almost as often he would slide back a body length or two, spraying frantic clouds of white dust, before resuming forward motion. Every few seconds a pile of snow behind one of them would collapse and slide downhill, spreading its material out until a new approach to the angle of repose was attained. Minutes — long minutes — passed. Those who had used the tank as a starting point were four or five yards up the slope, not too far behind the one who had started so long before. The rest, whose slipping had started at a lower level, had made little visible progress. The little fans and rivulets of sliding snow, first behind one and then another of the dozen red-and-black figures, were as hypnotic as the patterns in a bonfire; LaVerne had to wrench his attention away from them, suddenly realizing that he had more serious jobs than being a spectator. Slowly and painfully he hoisted himself to his feet. He could manage this at all only with the aid of ingenious lever-and-ratchet systems in the joints of his armor which let him concentrate on one part of the job at a time, and rest frequently without losing what he had gained. Once up, he turned slowly around, clarifying the mental picture he had already developed of the space they had fallen into. It was not too hard to infer how the cavern must have formed. As he had guessed, the layer of water ice under the sandstone had been bared by erosion at the top of the fold which formed the peninsula. The stone must have worn virtually to a knife edge; no wonder it had failed to support the tank’s weight once the underlying ice had gone. Ice was hard enough at Mesklin temperatures to stand mechanical erosion reasonably well, of course, but there was another factor operating here. Each year, as the giant world swung past periastron and the northern hemisphere began its summer, storms started sweeping ammonia snow from the virtually worldwide northern “ice” cap across the equator. This naturally buffered the local temperature near the freezing point of ammonia, which the Mesklinite student scientists had selected as the arbitrary control point for temperature in the scales they were developing. Once the protecting silica had eroded away, the solid ammonia encountered the equally solid water, and liquid resulted. Not only was some heat generated, but the solutions of the two had considerably lower freezing points than either compound alone — a fact which the present crop of students had all faced in their most elementary courses. The ice layer had melted, or dissolved, if one preferred to think of it that way, for fifty or sixty yards back from the edge of the protecting stone. Later in the season when the ammonia had evaporated, this would show a beautiful overhanging ledge extending probably for miles east and west. With luck, LaVerne would be able to see it; since the College had been set up less than half a Mesklin year before, no one had had the chance yet. LaVerne was not so much a scientist as a teacher. Still, he knew enough physical chemistry to wonder about the age of the peninsula — how long it would take the weight of overlying rock to squeeze the ice to the top of the fold and empty the filling from the sandwich. Maybe it had been going on for years already, and if they stayed in the cavern they could measure the creep of the south wall toward them. Maybe— A hoot that was almost deafening even through his helmet jerked his wandering mind back to the current realities. He knew about Mesklinite voices, of course, but no human being ever got used to their more extreme volumes. He turned as quickly as he could from the ice cliff to the slope which his students had been trying to climb. By the time he really got his eyes focused on the scene, the key events had happened; but it was obvious enough what they had been. The snow being kicked downhill by the climbers had been piling up against the tank. The earlier digging had left the vehicle almost without support on its downhill side, and what any thoughtful witness would have predicted had finally occurred. By the time LaVerne completed his turn, the machine was well into a full roll downhill toward him, and almost completely hidden inside a developing avalanche. The hoot, coming from several Mesklinites at once, had been stimulated by their discovery that they were involved in the slide; its upper edge was propagating rapidly toward the top of the slope and was already above the highest of the climbers. The man had little thought for his students just then. The rolling tank was heading straight toward him, and he could not possibly move fast enough to get out of its way. He was several yards from the bottom of the slope, but that might not be far enough. It all depended on whether the tank would reach the stone with enough energy to roll those few yards — let’s see; it looks as through it would land right side up; then onto its right side, then the top, then the left — that should bring it right to my feet. If there’s one more quarter-turn left in it, I’m flat. LaVeme wondered later how he was able to analyze the matter so calmly as the mass of metal came whispering down on him in its envelope of dusty snow. Actually it scarcely rolled at all, coming to rest with an ear-shattering clang on its right side. The man had a good heart — he would never have been allowed to serve on Mesklin otherwise — and was able to switch his attention back to his students almost at once; but the switch did his heart little more good than the juggernauting tank had. The Mesklinites were invisible. For a moment, real fear struck him — intelligent fear based on foresight, not just panic. If those people were gone, he would most certainly not get back to the College. Then little white fountains of dust began to erupt from various points near the bottom of the slope, and one after another the Mesklinites emerged. None of them had been buried deeply enough to matter. All was well. Except that there seemed no way to get out of the cave. Ideas flowed from all directions, since the Mesklinites were an imaginative lot; but none of these seemed very practical. Estnerdole suggested that the cave be explored in the east-west directions, on the chance that there might be a more usable way out. The objection to this was that not even the Mesklinites could see in the total darkness which obtained away from the area sunlit from their entry hole. Destigmet proposed cutting climbing notches in the cliff of water ice and reaching the top that way; unfortunately, ice met stone many yards from the hole, and there was no reason to hope that even the natives, insectlike as they appeared to human beings, could possibly crawl inverted along the stone ceiling. LaVerne, conditioned by a childhood on Earth, thought briefly of packing the snow to make a more reliable support and with it actually constructing steps up the slope. Fortunately for his reputation with the Mesklinites, he remembered in time that ammonia, unlike water, is denser in the solid than in the liquid phase. It does not, therefore, tend to melt under pressure; trying to make even a snowball out of the powdery stuff which had trapped them would be like trying to do it with a handful of sand. “All I can suggest,” he said at last, “is for some or all of you to start climbing again — maybe farther apart this time, so one person’s avalanche doesn’t involve everyone else. At least the tank won’t be a problem any more. It will be slow, but if even one of you can get to the top, he can go back to the College and get help. I can last here for days, with the air supplies in the tank, so there’s no emergency.”