It's late morning, and Crisafulli runs around his crew's loose collection of tents, stuffing waders and notebooks into a dry bag. He has the beard and baseball cap typical of many field scientists; a long ponytail hangs down his back.

As we hike toward a set of ponds through morning drizzle, Crisafulli launches into tour-guide mode. That yellowish moss is Racomitrium canescens. Those green-leafed trees are red alders, the yellow-leafed ones cottonwoods. Waist-high shrubs with crimson branches are willows. "We're really walking on the guts of St. Helens," Crisafulli explains. Every rock and handful of dirt that forms these hummocks came from the landslide that preceded the eruption.

As water collected in the hollows between hummocks, 150 new ponds formed. Some were no more than large puddles. Others, like Coldwater Lake, filled entire valleys. Thirty eventually washed out or overflowed. Such change could be expected, explains Monument Manager Tom Mulder. "We're learning what Mother Nature does" when left alone. Ultimately, however, fears of flooding forced officials to put public safety before the monument's natural processes.

Before 1980, Spirit Lake, on the north face of the mountain, held Pacific salmon that had swum upstream through the Columbia, Cowlitz and Toutle rivers. But the landslide buried the outlet from Spirit to Toutle. As lake levels rose, officials worried that the natural dam could catastrophically breach, setting off a chain reaction in dozens of other ponds and sending a massive flood down the Toutle, straight into Castle Rock, Longview and Kelso -- downstream communities with a combined population of 50,000.

So the Army Corps of Engineers built a mile-long concrete tunnel within the monument, allowing Spirit Lake to discharge into South Coldwater Creek, which flows west into Coldwater Lake. There, the Corps was forced to build another drainage outlet -- this time a cobble-lined channel -- connecting Coldwater Lake to Coldwater Creek.

The tunnel ensured that fish would never again find their own way to Spirit Lake, but it pales in comparison to what happened next. Landslide debris had increased the sediment load on the North Fork of the Toutle River more than a hundredfold, and the Corps feared it would raise riverbeds and facilitate future flooding. Since the agency is charged with flood protection, it built a sediment-retention structure -- a dam that slows the river so sediment can settle while clear water passes downstream. Although the structure lies a few miles outside the monument, it prevented migratory fish from spawning upstream.

That was the start of fish trucking. Since 1989, Washington Department of Fish and Wildlife has trapped fish below the dam and transported them to upstream tributaries. The goal is to re-establish historic runs of native fish, including coho salmon and steelhead (a form of migratory rainbow trout) which support sport and commercial fisheries. Both species are also listed as threatened under the Endangered Species Act. The results so far are murky. In a 2008 study, scientists found that trucked coho salmon hadn't spread from the few tributaries where they were released. The situation was complicated by the presence of introduced fish: In 1989, Washington Fish and Wildlife stocked 30,000 non-native rainbow trout in Coldwater Lake to provide angling opportunities within the monument. Since then, some of the trout have spread to nearby tributaries and may have interbred with trucked wild steelhead and wild cutthroat trout. But without detailed molecular studies, scientists can't tell what's going on.

"There can be a variety of unintended consequences in our attempts to help fish recover," says Brian Fransen, a Weyerhaeuser biologist who helped design the 2008 study.

Additional non-native rainbow and brook trout were placed in monument lakes that had been fishless before the eruption. Those fish also colonized monument streams and are undoubtedly changing the local ecology, Crisafulli explains.

Between the fish stocking and sediment dam, "we didn't have the opportunity ... to understand what fish were doing naturally," says Fransen. It's now impossible to untangle the human influences from how the mountain might have recovered on its own, and the fish story will never be clear-cut.

After stumbling down a hill of bare volcanic rock, Crisafulli enters a cool alder grove. Thin branches form a canopy over a tiny pond; one tree bears the mark of beaver teeth. It's hard to believe that all this was once rubble. The mountain's recovery is remarkable, but Crisafulli prefers the term "ecological response." Recovery implies a resetting of the clock back to pre-1980, when in truth, the return of life has been anything but predictable. The eruption wiped some areas clean, while in others, select creatures -- pocket gophers, insects, sprouting plant seeds -- weathered the blast underground. The result was a patchwork that offered a variety of niches. "Helens revealed that the chaos was like a lifeboat for organisms," says monument scientist Peter Frenzen. "From the standpoint of a bird, or small mammal, or amphibian, (the jumble) provided places for things to get started."

"A lot of it is like the lottery," Crisafulli says. "What species arrived first, which ones thrive." Scientists call these stochastic events: unpredictable and with definite effects. And some are driven by humans: The growth of neighboring tree farms, for example, shut out the understory and pushed an excess of elk onto the monument, where the forage is still good and there are no natural predators. Today, signs of their destruction are everywhere: clumps of ripped-up moss, collapsed gopher tunnels, cottonwood trees like twisted bonsai. Mulder has seen stands of Douglas fir "so heavily browsed it looks like someone's been hitting them with a lawnmower."

These far-roaming herbivores also spread seeds with their droppings. At one point, Crisafulli drops to the ground and runs his hands through a clump of ordinary-looking grass. "White clover and an exotic grass from Eurasia," he observes -- invasive plants, courtesy of the elk.

Two years ago, the Forest Service launched a pilot program to increase hunting access within the monument. The idea wasn't to kill lots of elk (12 were bagged in the newly opened areas during the 2008-2009 hunting season) but to keep the "very natural elk horde" moving around and overgrazing less, says Mulder. Never mind that it's difficult to know what "natural" means in this case.

The monument might have been conceived as a living lab, but boundaries that exist on paper are fluid in the real world, and the ongoing experiment is far from controlled. It is, notes Mulder, "a constant landscape of change," one in the process of reclaiming itself. Back in 1981, for example, when Corps engineers built the artificial channel out of Coldwater Lake, they lined the sides with steep slopes of riprap. It was meant to force the water on a linear path, yet 30 years later, the stream has eroded, slicing below the riprap into the underlying dirt. To the casual observer today, there is nothing unnatural about the meandering stream flowing between the evenly-placed rock. Everything blends together and the stream flows on, carving its own sinuous path down the mountain.