With three camps established above the cave, which serves as a sort of base camp to return to from time to time, they are making fair progress. Each night only a few of them are in any given camp. They are forced to use oxygen for almost all of the climbing, and most of them sleep with a mask on, the regulator turned to its lowest setting. The work of setting up the high camps, which they try to do without oxygen, becomes exhausting and cold. When the camps are set and the day's climbing is done, they spend the shadowed afternoons wheezing around the camps, drinking hot fluids and stamping their feet to keep them warm, waiting for the sunset radio call and the next day's orders. At this point it's a pleasure to leave the thinking to Eileen.
One afternoon climbing above the highest camp with Eileen, Roger stands facing out as he belays Eileen's lead up a difficult pitch. Thunderheads like long-stemmed mushrooms march in lines blown to the northeast. Only the tops of the clouds are higher than they. It is late afternoon and the cliff face is a shadow. The cottony trunks of the thunderheads are dark, shadowed gray—then the thunderheads themselves bulge white and gleaming into the sunny sky above, actually casting some light back onto the cliff. Roger pulls the belay rope taut, looks up at Eileen. She is staring up her line of attack, which has become a crack in two walls meeting at ninety degrees. Her oxygen mask covers her mouth and nose. Roger tugs once—she looks down—he points out at the immense array of clouds. She nods, pulls her mask to one side. “Like ships!” she calls down. “Ships of the line!"
Roger pulls his mask over a cheek. “Do you think a storm might come?”
“I wouldn't be surprised. We've been lucky so far.” She replaces her mask and begins a layback, shoving the fingers of both hands in the crack, putting the soles of both boots against the wall just below her hands, and pulling herself out to the side so that she can walk sideways up one of the walls. Roger keeps the belay taut.
Mars's prevailing westerlies strike Olympus Mons, and the air rises, but does not flow over the peak; the mountain is so tall it protrudes out of much of the atmosphere, and the winds are therefore pushed around each side. Compressed in that way, the air comes swirling off the eastern flank cold and dry, having dumped its moisture on the western flank, where glaciers form. That is the usual pattern, anyway; but when a cyclonic system sweeps out of the southwest, it strikes the volcano a glancing blow from the south, compresses, lashes the southeast quadrant of the shield, and rebounds to the east intensified.
"What's the barometer say, Hans?"
“Four hundred and ten millibars.”
“You're kidding!”
“That's not too far below normal, actually.”
“You're kidding.”
“It is low, however. I believe we are being overtaken by a low-pressure system.”
The storm begins as katabatic winds: cold air falling over the edge of the escarpment and dropping toward the plain. Sometimes the force of the west wind over the plateau of the shield blows the gusts out beyond the actual cliff face, which will then stand in perfect stillness. But the slight vacuum fills again with a quick downward blast, which makes the tents boom and stretch their frames. Roger grunts as one almost squashes the tent, shakes his head at Eileen. She says, “Get used to it—there are downdrafts hitting the upper face more often than not.” WHAM! “Although this one does seem to be a bit stronger than usual. But it's not snowing, is it?"
Roger looks out the little tent-door window. “Nope.”
“Good.”
“Awful cold, though.” He turns in his sleeping bag.
“That's okay. Snow would be a really bad sign.” She gets on the radio and starts calling around. She and Roger are in Camp Eight (the cave is now called Camp Six); Dougal and Frances are in Camp Nine, the highest and most exposed of the new camps; Arthur, Hans, Hannah, and Ivan are in Camp Seven; and the rest are down in the cave. They are a little overextended, as Eileen has been loath to pull the last tents out of the cave. Now Roger begins to see why. “Everyone stay inside tomorrow morning until they hear from me at mirror dawn. We'll have another conference then.”
The wind rises through the night, and Roger is awakened at 3:00 A.M. by a particularly hard blast to the tent. There is very little sound of the wind against the rock—then a BANG and suddenly the tent is whistling and straining like a tortured thing. It lets off and the rocks hoot softly. Settle down and listen to the airy breathing WHAM, the squealing tent is driven down into the niche they have set it in—then sucked back up. The comforting hiss of an oxygen mask, keeping his nose warm for once—WHAM. Eileen is apparently sleeping, her head buried in her sleeping bag; only her bunting cap and the oxygen hose emerge from the drawn-up opening at the top. Roger can't believe the gunshot slaps of the wind don't wake her. He checks his watch, decides it is futile to try falling back to sleep. New frost condensation on the inside of the tent falls on his face like snow, scaring him for a moment. But a flashlight gleam directed out the small clear panel in the tent door reveals there is no snow. By the dimmest light of the lamp Roger sets their pot of ice on the square bulk of the stove and turns it on. He puts his chilled hands back in the sleeping bag and watches the stove heat up. Quickly the rings under the pot are a bright orange, palpably radiating heat.