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The Maretian

by Kris Overstreet

Chapter 117: Sol 204

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AMICITAS FLIGHT THREE – MISSION DAY 205
ARES III SOL 204

The castaways named it The Stump.

It was a rough-broken giant end of a quartz crystal at first, sticking out not quite a meter from the surface of the cave floor. One attempt, and only one, had been made to remove it, and that attempt had made clear that it was either still attached to the immense geode wall meters below all the dirt, or else it was so large that it might as well be. So, when the farm had been laid out, it was lopped off level at the top, slightly too large for a stool and too small for a table, but still convenient to set tools and other things on as needed.

The farm had been built around it, the crystal bracketed by two of the hot water lines running the length of the growing area. After the methane blowout, when the sinkholes happened, one sinkhole included the area around The Stump. The dirt had sunk almost two feet; The Stump, not one inch. The refill around The Stump hadn’t quite come up as high as the previous level, so the top of The Stump now rose just above pony chin height, which made it uncomfortable to use as a table.

But Starlight Glimmer had found it quite convenient to use for another purpose, with the aid of one of the mostly-full mana batteries that had been retained at the Hab for emergencies.

Now the air above The Stump lit up with a magical hologram, a three-dimensional chart of the entire cave from its origins near the ancient volcano’s magma chamber to and beyond the hole where the airlock had been sited.

The hole which, it turned out, had been more in the way of a skylight.

The farm chamber of the gem cave was far and away the largest section. Though other sections farther back were wider, the ceiling was taller- and the rock substrate under all the dirt and permafrost much deeper- in that first room. The dirt immediately under the original skylight had compressed over eons into sandstone, and it had been that sandstone that had originally supported the airlock, before the sealing spell had turned it effectively into concrete. Its color had been the same as the grey non-crystal quartz of the cave roof layer, so they hadn’t noticed the difference at the time, thinking it was the cave floor.

Buried under the sandstone, more quartz crystals ran well beyond the modern cave entrance, finally terminating in a jumble of collapsed lava, quartz, and other rocks about twenty feet underneath the regolith at the base of Site Epsilon’s northeast face.

Starlight’s horn flashed, and sections of the cave diagram flared. “The scan of the area shows that most of the subsidence is over,” she said. “There are only a few small patches of the original permafrost remaining under the soil- here, here, and here. Most of it has melted and seeped either to the well, here-“ she pointed to the graph at the recent excavation, “-or to the bottom of the sealed space, where a new foundation of permafrost is freezing back into place with the loss of cave heat.”

Starlight highlighted the area at the base of the farm area, and the soil below the cave entrance, with its still mostly-intact permafrost. “As best I can guess, the runoff from the water heating system ran downstream into the Tangled Hallway-“ (the small second chamber, crowded with floor-to-ceiling and wall-to-wall crystals that took careful maneuvering around; the first chamber was just The Farm) “-and as far as Lunch Buffet.” (This was the third chamber, about half the size of the farm, with its pockets of different-colored quartz, from which most of the mining for Fireball’s meals had been done.) “This caused some runoff of soil along the way, but only a trickle got into the Crack-“ (the narrow gap between the third and fourth chambers) “-and anything that got farther froze, at least initially.

“But what we never thought about was that the vast majority of that water was gradually seeping down into the soil. It found cracks in the permafrost near the chamber walls and got below it- and a good thing, too.” She traced the downward slope of most of the lower levels of the cave farm soil. “Some water got trapped in the depths of the Hallway and the Buffet, but I’m guessing about half of all we dumped cycled through the sand near the door into Hallway or earlier, through the permafrost cracks- which enlarged in the process- and flowed downslope, into the sandstone here.” She pointed to a disturbing-looking undercut in the strata just beyond the sealed borders of the cave.

“The water was still liquid at this point,” Starlight said. “Which means by Mars standards it was still red-hot. But it was flowing away and dumping its excess heat outside the cave until I sealed it up. It also carried away with it melted water from-“

“Wait a minute,” Mark said. “That’s a breach. Why didn’t we lose air that way?”

“We did. But only a very, very little at a time,” Starlight said. She pointed at the overhang again. “Water is heavier, so it could force a way through where air wouldn’t. But that might have changed if this eroded point had given way entirely. There must be a crack or something that allowed water to flow here like… like…” Starlight tried not to make a face as she ran into a word she still didn’t have in English. Those came less often, but sometimes she found one. “Like a layer of flowing water in rock or sand,” she said in one quick breath.

“Aquifer?” Mark offered. “Where springs come from?”

“I thought springs came from metalworkers,” Dragonfly quipped.

Starlight moved on before futile attempts to correct the changeling ensued. She was pretty sure she only did it to appear silly, anyway. Bad habit. “Show me the word when we return to the Hab, Mark,” she said. “Anyway, the weight of soil and permafrost down slope prevented a rapid blowout. But if this had worn through a bit more, the soil under the entrance might have collapsed. Then we definitely would have had a breach. Or possibly an avalanche.” That was a word she’d learned from an episode of Grizzly Adams. “And most likely at least one of us would have been here, without our suits, when it blew.”

A few moments of silent contemplation of that prospect seemed enough.

“Of course, the modified Instant Foundations spell put an end to that,” Starlight said. “But it also put an end to the outflow of water. And to the outflow of heat. The difference wouldn’t have been much, but it would have been… would have been…” She tossed her head in an involuntary gesture of frustration to not knowing the English for cumulative. “It added up.”

She pointed to the small voids remaining under the cave farm’s surface, then farther back in the cave to the much larger pockets still vacant in the chambers farther back. “The permafrost in the cave was particularly thick all the way through,” she said. “I don’t know how that could be, but-“

“I have an idea,” Mark said. “There’s a theory that about once in a million years or so Mars experiences a brief warm period. Maybe because of a volcanic eruption, maybe orbital eccentricity, maybe a meteorite, whatever. The atmosphere thickens up enough to allow liquid water to flow on the surface. And as dry as Mars is now, it still has a lot of water locked up places- the permafrost layers, the polar caps, and like that. We haven’t got enough proof to support or overturn that theory yet, but it would make permafrost layers in the cave possible.”

“Thank you, Mark,” Starlight said. “Anyway, the lower levels of the permafrost had a lot of methane. The layers of permafrost beyond the cave- all of them, even the one above the cave- still have a lot of it. But so long as the water was flowing, the heat in the lower levels never quite got high enough for a large-scale release. But when the liquid water had nowhere to go…”

“Cave fart,” Fireball rumbled.

“Right.” Starlight tapped the remaining vugs in the chart and said, “I learned a couple of tricks from Maud about moving minerals around, so I can fill these pockets without much trouble. It’ll take most of the rest of this battery,” she tapped the battery at her hooves that powered the display, “to do that. But then what?”

“Must let water run again,” Cherry said carefully. “The farm will die if we don’t. Not enough heat.”

“But if we do,” Mark said, “all the water will build up about twenty meters below us and work back up through the soil until we have a bog.”

“Pump it out?” Spitfire suggested.

“We need some water for the crops,” Mark said.

“Also, no pipe left,” Dragonfly said.

“And we don’t want to breach the cave for an exit point,” Mark added. “The water would be sucked out, and then so would the air.”

“If that happened the water would shut off automatically,” Dragonfly said. “Home won’t let us pull a constant vacuum on the space base water tanks.”

Mark rubbed the small of his back. “But carrying the spent water out a bucket at a time is backbreaking work,” he said. “And not all that effective.”

“We’ll have to let the water run as far to the back of the cave as we can, at first,” Starlight said. “Can we make a trench out of Amicitas hull pieces- not a trench, but a made-thing water runs along? Like on roofs or sidewalks?”

“Gutter,” Mark and Dragonfly said at once.

Spitfire smirked. “That where you minds is?”

Starlight gave the Wonderbolt a look. She knew Spitfire struggled with English more than any of the others. How did she come up with that one? Also, if gutter was the word for gutters, why did so many of those TV shows make it sound like a dirty place? What kind of slovenly pony or underfunded town cleaners would let a gutter get dirty? It wouldn’t do its job-

Starlight shook her head. I wish I could speak to Applejack or Rainbow Dash privately, she thought. I need to know if Twilight Sparkle’s obsessive thinking is contagious. Aloud she said, “Can we build one, and how long?”

Fireball, the self-designated Keeper of the Salvage, thought about it. “Yeah,” he said. “It leak, though. Lay one end on top next piece down, make waterfall, that help. Maybe… maybe two hundred meter?” he said.

“Not quite to the Crack,” Mark muttered.

“Make well by Crack,” Fireball suggested. “Keep it there.”

“It’ll seep down and turn the whole floor of the Buffet to mud,” Mark warned.

“Too cold in there now,” Fireball said, shaking his head. “Freeze up first.”

“Why not make a strip of compressed dirt?” Dragonfly asked. “Use the same spell you sealed the cave with.”

Starlight shook her head. “We need more magic to do everything,” she said. “We need batteries for testing engines and for the Sparkle Drive. We need it so I can teleport the excess water out- it’s the only way I can think of to do it quickly and safely. We need it for magic fields so Cherry can revive the farm. But we can’t get more magic without more batteries, and we’ve used up the batteries twice now on other things.”

She sighed, shaking her head. She’d hoped that making batteries would be an exponential growth process- two batteries, then four, then eight. But as the number of batteries grew, so did the demand for magic. It was just too useful- and too integral to everything the ponies could contribute to survival and escape.

“After today, no magic for ten days,” she said. “Unless life or death emergency. Then I make new batteries –six or eight, depends on how much power I have then. Those batteries get put aside, only to be used to make more batteries. Then I can turn the well,” she pointed to the big hole at the back of the chamber, “into a concrete cistern, with batteries I can use to teleport the contents outside the cave walls when we need to.

“That’s the long-term solution. Once we have enough batteries, the other problems solve themselves. But batteries first.” Starlight tapped the battery under her hoof, causing the diagram to flicker and almost collapse. “Until then, we make do.”

“Okay,” Mark said. “So I guess we fill the voids under the surface to prevent more sinkholes, then go back to base and make plans for a runoff gutter.”

“We?” Starlight raised an eyebrow and smirked. Her horn flared, and a large lump of dirt scooped itself up from the walls of the well. It floated over to a bare spot of the farm, filled back in after a sinkhole, where the chart showed a pumpkin-sized void underneath. She stepped over to the lump of dirt, wrapped her magic around her hoof, and stomped down hard and in a very precise way on the lump.

WHUMP.

She stepped away, the surface perfectly flat again.

Tomorrow she began another ten-day magic fast. Today she still had two-thirds of a battery, and she was going to enjoy it.

Mark looked at Cherry Berry and Dragonfly. “How did she do that?” Starlight heard him ask.

Cherry Berry shrugged. “Don’t know,” she said. “I never work on rock farm.”

“On what?”

Starlight levitated the two sample shovels to Mark and Fireball. “Get digging,” she said. “Outside. We’ll need to bring in dirt for those big voids under the Buffet. And then you need to bury those pipes.”

Author's Notes:

A week of bed rest has done Starlight a world of good. (And if you're wondering, she looked up "cistern" the night before, while thinking her plans through.)

Half an hour (as I type this) until tonight's KWLP. It's a Weird Al special, since I went to a Weird Al concert last night two and a half hours away... and got home very late.

Next Chapter: Sol 207 Estimated time remaining: 17 Hours, 31 Minutes
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