Ray Suarez: This is NPR’s Morning Edition, I’m Ray Suarez.

We rejoin a National Geographic Radio Expedition now, one we began yesterday in Yellowstone National Park. NPR’s Alex Chadwick first visited Yellowstone ten years ago, when wildfires ravaged the park from June until they petered out in the snows of November. In all, 800,000 of the park’s more than two million acres were scorched. The fires of 1988 raised fears the park would be scarred for generations. Alex recently returned to see how the park is doing.

Chadwick: (SOUND EFFECT: MALLARD LAKE) The biology is beautiful—forests and animals—and the mountains are magnificent—the Rockies and the Continental Divide. But underneath it all, the true soul of Yellowstone is fire and steam. Water comes out of the ground here boiling hot. (SOUND EFFECT: BUBBLING VENT)

Bob Smith: No one’s ever studied a system like this. There’s no hot spot on a continent; all the hot spots are in oceans, except for Yellowstone.

Chadwick: Bob Smith, a University of Utah physicist and co-author of a soon-to-be-published book on Yellowstone’s bizarre geology.

Smith: It’s a gigantic energy center of both heat uplift and earthquakes interrupted periodically by volcanoes. Yellowstone is not just sitting on a volcano; it is a volcano.

Chadwick: Yellowstone is a volcano?

Smith: Yeah, it’s a volcanic system. It’s so big you can’t see it.

Chadwick: But you can see the heat, explicit and aroused, as nowhere else in the world. It’s why people have always come here (SOUND EFFECT: BOARDWALK AMBIANCE), why they still come: to find a place on the long, curved bench seats at Old Faithful and cheer its spectacular display. (SOUND EFFECT: OLD FAITHFUL GEYSER ERUPTING)

The last time I saw this place, everyone but the fire crews had fled. The hillside a half-mile to the west was burning; more smoke came from behind us. I kept glancing back to see if we might be surrounded, and I noticed others doing the same. The sky grew new colors, shades of orange that a sunset never saw. The dark air was sifted with fiery debris; my breath came in shallow, frightened gasps.

When the geyser quieted again, some people stopped to talk about Yellowstone today.

First unidentified woman: I was here the year after the fires, and I was very, very upset when I went through the canyon area, because everything was just so black. So today when we were driving in I was expecting the trees to be back, and it still looks like the fires just happened. But if you look very closely, you see all the little saplings and stuff emerging. It’s very exciting to see that.

Unidentified man: We were here six years ago, and we had a wonderful tour guide that explained to us that fires are not necessarily a bad thing, that forest is supposed to burn on a 200- to 600-year cycle. That’s the way nature designed it; it’s only our intervention that messes that up. And that seems pretty much okay. I mean, the burned-out stuff is as interesting to look at as the green stuff. Actually, it’s pretty awesome to look at a whole forest that’s just sticks standing there. It’s a lot different.

Unidentified boy: I think the burned part, like my dad said, is just as good as the part that’s green. It’s still really cool to look at.

Chadwick: But for others, the remnants of the fires are an ugly intrusion.

Second unidentified woman: I’m really disappointed in the way it looks. I think it looks very devastated, and I don’t care for the way it looks now at all. (SOUND EFFECT: WIND)

Chadwick: Patches of burned forest extend for miles in places—bare trunks, dead but still standing. Some call them ghost trees, for their silver-gray color and their spooky, silent presence. In order for a tree to actually burn, a fire must first boil away all its water.

Don Despain: Those that are charcoal on the outside, those trees were dead at the time the fire went through.

Chadwick: Don Despain, a forester with the [United States National] Park Service when the fires broke out and a leading theorist for the importance of fire in a healthy forest.

Despain: The ones that are kind of a silver color—that’s where the bark’s fallen off—they were alive at the time the fire came through here, and it didn’t burn into the wood.

Chadwick: We are standing in a burned section, just over the ridge from a road that leads to Yellowstone’s headquarters ten miles away. All the big trees around us—50-60 feet [15- 18 meters] tall—are dead.

[To Despain] As you look around and see this forest here now, is this what you intended?

Despain: Yes, this is what I had in mind. Fire is a natural part of the system. It’s been here long before we have. Apparently, fire’s been a part of the wood environment as long as there’s been plants on the Earth.

Chadwick: The forest is adapted to fire; some trees put out seeds that need fire to open. Where the hillside rises a short distance away, a couple of dozen elk browse contentedly on the shrubs and low greenery and new trees growing everywhere.

Despain: The lodgepole pines are 3 and a half [or] 4 feet [1.1 or 1.2 meters] to 8-feet-tall [2.4 meters]. They’re growing 16 to 18 inches [41 to 46 centimeters] a year. The ground cover is back to what it was before the fire, and it’s a ten-year-old forest that’s well on its way to recreating the forest that was here in 1988.

Chadwick: Aspen seedlings are sprouting. Now, that meant nothing to me until a forester explained that aspens here normally reproduce through a network of roots spreading and poking up where they can; actual seed seedlings had almost never been seen.

For the most part, animals could flee the fires, and did. They are back. Yellowstone is flourishing. Visitors are back too; the park may set a record this year.

Despain: The basis for managing Yellowstone is to maintain an area without human interference. And fire suppression is a human interference. 1988 wasn’t the first time it burned, and it won’t be the last time, either.

Chadwick: Still, the somber aura of the burned parts has the power to trouble us, more so on learning how the trees really died, which was not directly from the fire. Rather, the fire destroyed the delicate inner-bark layers of cells that carry food to the roots. In the months following the fires of ’88 about one-third of the Yellowstone forest slowly starved to death. The ghost trees are bones, not yet collapsed.

Forester Don Despain.

Despain: All of the trees that were alive at the time that the fire went through are still here—most of them still standing. They’ll begin to fall quite rapidly now, and in some places most of them have fallen.

Chadwick: In ten years will all these trees still be standing here?

Despain: In the next ten years most of these trees will fall.

Chadwick: For all the controversy over what happened ten years ago, the soul of Yellowstone is fire and steam.

The Utah physicist Bob Smith will tell you the story is in the rocks and in places like the Norris Geyser Basin, which reveal Yellowstone’s volcanic nature very clearly—in its past, and in its future too.

A big, big fire is coming—brimstone, cataclysms. The only question is, when?

Smith: If you look at the smaller eruptions, I’ve calculated the average from 600,000 years ago to the present, and the average is 19,000 years. So the fact is we haven’t had an eruption for 70,000 years. So one would say, well, we’re three cycles behind.

Chadwick: But there’s also the matter of the big eruption, the 600,000-year eruption, and it’s been 600,000 years since the last big eruption.

Smith: That’s right, 630,000 years since the last eruption. And the real question is, are we currently in the tail end of the stage of that eruption, or are we in the beginning stage for a new eruption? We don’t know.

Chadwick: Yellowstone’s natural fire policy remains in effect, with the Park Service fighting only those fires started by people, accidentally or on purpose. But when Yellowstone’s inevitable end arrives, no policy will make the slightest difference.

For Radio Expeditions, this is Alex Chadwick, NPR News, Yellowstone.