Mattison has just about enough time to realize that he has survived the explosion when he registers the force of an inrush of cool air that’s swooping in from all sides to fill the gap where the geyser had been. It isn’t strong enough to knock anybody down, but it does make you want to brace yourself pretty good.
And then comes the heat; and after it, the lava flow.
The heat is awesome. Mattison’s suit catches most of it, but enough of the surge gets through his insulation so that he has no doubt at all about its intensity. It is what he calls first-rush heat: the subterranean magma mass has been cooking whatever deposits of air have surrounded it down there, and all that hot air, having had noplace to go, has gone on getting hotter and hotter. Now it all comes gleefully zooming out at once. Mattison recoils involuntarily as though he has been belted by an invisible fist, steadies himself, straightens up, looks around to check up on his companions. They’re all okay.
The lava, having busted through the pavement at last, follows right on the heels of that hot blast. A glowing red-orange river of it, maybe two or three feet deep, flowing down the middle of the street, taking the line of least resistance between the buildings as it heads in their direction.
“Hose!” Mattison yells. “Pump! Hit it, you bozos, hit it right down front!”
The lava is moving faster than Mattison would prefer, but not so fast that they need to retreat, at least not yet. It’s actually three separate streams, each runnel six to eight feet wide, traveling in parallel paths and occasionally overlapping in a braided flow before separating again. The surface of each flow is fairly viscous from its exposure to the cool air, darker than what is below and showing irregular bulges and lobes and puckerings, which break open now and then to reveal the bright red stuff that lies just below. Here and there, narrow tongues of dark congealed lava rise above the stream at sharp angles like sleek fins, making it seem as though lava sharks are swimming swiftly downstream through the fiery torrent.
As the water from their big hose hits the first onrush of the flow, a scum of cooling lava starts to form almost instantly atop the middle stream. The front of it begins to change color and texture, thickening and turning gray and wrinkled, like an elephant’s hide.
“That’s it!” Mattison tells his men. “Keep hitting it there! Smack in the middle, guys!”
The water boils right off, naturally, and within moments they are able to see nothing in front of them once again except a wall of steam. This is the most dangerous moment, Mattison knows: if the lava, pushed toward them by whatever giant fist of gas is shoving it from below, should suddenly increase its uptake velocity, he and his whole team could be engulfed by it before they knew what was happening to them. For the next few minutes they’ll be fighting blind against the oncoming lava flow, with nothing to guide them about its speed and position but Mattison’s own perceptions of fluctuations in its heat.
The heat, at the moment, is really something. Not as fierce as it had been in the first instant of the breakout, no, but powerful enough to tax the cooling systems of their lava suits practically to their limits. It feels like a solid wall, that heat: Mattison imagines that if he leaned forward against it, it would hold him up. But he knows that it won’t; and he knows, also, that if things get much hotter they will have to back off.
What he is trying to do is to build log-shaped strips of solidified lava along the front of the row, perpendicular to the line of movement. These will slow its advance as the fresh stuff piles up behind them. Then he can raise the angle of the hoses and start pumping the water upward to form larger blocks of lava, which he will eventually link to create his dam. And in time he will have buried the live lava at its source, entombing it beneath a little mountain of newly created rock and thus throttling the upwelling altogether.
The theory is a nice one. But in practice there usually are problems, because the lava, unlike your average river, tends to advance at a variable speed from moment to moment, and you can build a lovely little log-jam or even some good-sized retainer blocks and nevertheless a sudden fast-moving spurt of molten stuff will spill right over the top and head your way, and there is nothing you can do then but drop your hoses and run like hell, hoping that the lava isn’t traveling faster than you are.
Or else, as Mattison knows all too well, your dam will work very effectively to halt the lava in its present path—thereby inducing it to take up a different path that will send it rolling off toward some still undamaged freeway or still unruined houses, or maybe pouring down a hillside into another community entirely. When you see something like that happening, you need to move your whole operation around at a 90-degree angle to itself and start building a second dam, not so easy to do when you are operating with two-ton pumps.
Here, just now, everything is going sweetly so far. It’s a tough business because of the extreme heat, but they are holding their own and even managing to achieve something. They have been able to maintain themselves at a distance of about half a block from the front edge of the lava flow without the need to retreat, and Mattison can see, whenever the steam thins out a bit, that the color of the lava along the edge is beginning to turn from gray to a comforting black, the black of solid basalt. A pump crew from some other Citizens Service House has arrived, Mattison has been told, and is building a second lava dam on the opposite side of the breakout. The fire crews are at work in the adjacent blocks, hosing down the structures that were ignited by the initial geyser of lava fragments.
If visibility stays good, if the water supply holds out, if the pump doesn’t break down, if the lava doesn’t pull any velocity surprises, if some randomly escaping gobbet of hot rock doesn’t go flying through the air and melt one of the hoses, if there isn’t some new eruption right under their feet, or maybe an earthquake, if this, if that—well, then, maybe they’ll be able to knock off in another hour or two and head back to the house for some well-earned rest.
Maybe.
But things are beginning to change a little, now. The lava is penned up nicely in the middle but the bulk of the flow has shifted to the right-hand stream and that one is gaining in depth and velocity. That brings up the ugly possibility that Mattison’s dam is achieving diversion instead of containment, and is about to send the entire flow, which has been traveling thus far from west to east, off in a southerly direction.
Volcano Central is monitoring the whole thing by satellite, and somebody up there calls the problem to Mattison’s attention via his suit radio about a fifteenth of a second after he discovers it for himself. “Start moving your equipment to the right side of your dam,” Volcano Central says. “There’s danger now that the lava will start rolling south down San Dimas Avenue into Bonelli County Park, where it’ll take out the Puddingstone Reservoir, and maybe keep on going south until it cuts the San Bernardino Freeway in half on the far side of the park. A piece of the 210 Freeway will also be at risk down there.”
The street and park names mean nothing to Mattison—he has never been anywhere near San Dimas before in his life—and he can form only a hazy picture of the specific geography from what Volcano Central is telling him. But all that matters is that there’s a park, a reservoir, and an apparently undamaged stretch of freeway to the south of here, and his beautifully constructed lava dam has succeeded in tipping the flow toward those very things, and he has to hustle now to correct the situation.