- [Charlie] As you walk around, you just see the way in
which life comes back after a large, catastrophic disturbance. - [Narrator] Do not mistake
this volcanic landscape for a moonscape. Life has returned with a vengeance. - Under close inspection, if you walked around on
these bare hillslopes, what you would find is a
staggering number of species that are actually there,
but all in very low numbers. - [Narrator] At Mount Saint Helens, it's what happened after the eruption that exploded scientists'
notions of ecological recovery. And it's revealed multiple mysteries. Why do giant fish grow unbelievably fast and then inexplicably die? How is it that amphibians
absolutely flourish at a time when they're in
trouble across the Cascades? And what are the ripple effects of the ancient logs floating
over a fifth of Spirit Lake? - There is not a single theory or model that's adequately
explained what we've seen at Mount Saint Helens. - [Narrator] Nowhere
do these complex tales of death and life coalesce
as they do at Spirit Lake. It's Charlie Crisafulli's
living laboratory. Dozens of times each year, he treks miles to Spirit Lake to examine the water and its inhabitants. He's a Forest Service ecologist, and he's spent his entire
career studying Mount Saint Helens ever since the eruption. - [Charlie] Well, I don't think
anyone anticipated the pace, the rapid pace at which
Spirit Lake responded. - [Narrator] Scientists
wanted Spirit Lake left alone, and so it has remained. - [Charlie] We need to really think about what was here before. - [Narrator] Before the eruption seems hard to fathom anymore. A majestic, old-growth forest of hemlocks and noble and silver firs
covered every hillside. Camps and cabins dotted the lake's edge. May 18th, 1980 changed everything. The mountain exploded with
the force of 10 megatons as powerful as a nuclear weapon. 1,300 feet of the mountaintop rained down. It annihilated entire forests. The blast zone covered 250 square miles. And the largest landslide
in recorded history headed straight for Spirit Lake. - Surged into the lake, pushed all of the water out of the lake, and when it did, it traveled about 800 feet up
onto the adjacent hillsides and carried the forest, the
soil, and all its inhabitants back down into the lake basin. - [Narrator] So much of
the mountain landed here. The bottom of Spirit Lake rose 200 feet, and it spread out to twice its area. - [Charlie] So it's hard to believe that an entire lake can
be physically moved, but indeed that's what happened here. Most life was obliterated. - [Narrator] After the eruption, water visibility measured in mere inches and felt as warm as body temperature. Within hours, bacteria multiplied, followed by months of new
waves of bacteria and microbes. But within a few years,
lake life had returned. - Well, more than just returned. I mean, by 1989, a mere nine
years after the eruption, the lake, in many respects, was typical of many other
lakes in the Cascades. But it was never going
back to its former self. (water lapping) - [Narrator] Today, Spirit
Lake generates more nutrients than ever before. It has never been this productive. Life in Spirit Lake
rebounded, except fish. The eruption had cut off the Toutle River. Then one day in the early 90s, someone spotted a rainbow trout. - [Charlie] We're pretty certain that those fish were
placed in here by someone. It was not a planned stocking by Washington Department
of Fish and Wildlife. - [Narrator] Whoever planted the fish interfered with scientists' plans to watch the lake recover
completely on its own. The fish then became
part of the experiment. - [Charlie] Well, this is
something we do monthly from the time of ice
out through late autumn when snow becomes a problem for access. - [Narrator] Every time Charlie
Crisafulli surveys the fish, he finds the same thing. - [Charlie] Oh, there's a
tremendous number of fish. - [Narrator] Rainbow
trout have multiplied. They thrive in Spirit Lake's
now food-filled waters. - [Charlie] The fish
are incredibly healthy. The population appears to be very robust. - [Narrator] With so many insects, the fish eat very well and have grown extremely
large remarkably fast, three times faster than normal. - [Charlie] It points to the fact that there's a tremendous
food resource in the lake. Beyond that, we simply don't know. - [Narrator] The trout
present a double mystery. First, they're giant. Many weight four to five pounds. - [Charlie] They're quite young. These fish are only three
and four years of age and attaining the size and weight. - [Narrator] Spirit Lake's
fish, at four years old, are larger and longer than fish three times older
elsewhere in the Cascades. The second puzzle. - [Charlie] Okay, incoming. - [Narrator] They're not
nearly as old as they look. When Charlie takes measurements, he also samples their scales. Scales reveal the fish's age. Every single trout is young. In fact, by five years old, they're dead. - [Charlie] The oldest
fish here is probably, we've got one or two fish
that is five years of age. - [Narrator] They should
live 12 to 15 years. Their early and certain
deaths remain a mystery. In Spirit Lake, water temperature readings are now back to normal. - [Charlie] And we'll drift
right into the log now. I'm in neutral. I'm gonna kill the motor. There we go. Spirit Lake is the most
well-documented lake in the Mount St. Helens blast area and may very well be the
most thoroughly studied lake following a volcanic blast
there is anywhere in the world. - [Narrator] As he works, Charlie's hanging on to a tree
impaled in the lake bottom. It is just one of the
tens of thousands of trees blasted off the hillside. Most of them still
float on the lake below. - [Charlie] Well, I think the wood is largely underappreciated, and clearly that's a place where we need to start
focusing our attention in terms of research. - [Narrator] It is Spirit
Lake's most famous feature. Floating logs bump and bang each other as far as the eye can see. - Take a look at this. It goes on for about 15 to 20% of the lake is covered with floating
logs of the ancient forests that once surrounded
the Spirit Lake basin. And still, here we are 27 years later, and it's still afloat. - [Narrator] Hemlocks
and true firs have sunk. Doug firs and cedar have not. - [Charlie] But I'm really surprised that they haven't become waterlogged and sunk to the bottom. - [Narrator] Wind blows the logs from one end of the lake to the other. They always seem to mass together. With such constant motion, the logs prevent something that used to happen every single year before the eruption, ice. Spirit Lake does not freeze anymore. - [Charlie] So if you look across this expansive coverage of the lake where light simply can't penetrate. - [Narrator] Sunlight
ends up largely blocked wherever the logs happen to float. - [Charlie] Sunlight is very
important for lake systems. It's so important to the
very base of the food web. In this case, phytoplankton. - [Narrator] The logs do provide habitat. - [Charlie] Undoubtedly, the log mat is a large nursery for insects in fueling vigorous emergences. - [Narrator] But the logs
are not just home to insects. They're fodder for new plants, even shrubs and trees
that don't normally float. - Alder and willow trees actually growing out of the floating log mat. We have a forest developing out on the log mat, which is truly bizarre. - [Narrator] And there's
a new forest taking root on the hillsides around Spirit Lake. It's sparse, but for the
first time since the eruption, trees are now producing
seeds of their own. Cones are back. - And so now we're going
to eventually see an apron of conifers down-slope
from this parent tree, and this is the initiation of the next forest to come
within the Spirit Lake basin. - [Narrator] Over a hill and one-and-a-half miles from Spirit Lake, St. Charles Lake sits surrounded by trees flattened in the blast. - And in this basin, there was
a great deal of survivorship, and that had to do with
the timing of the eruption. - [Narrator] The eruption
occurred in the morning. Nocturnal animals were
safely back underground, and the cold of winter had not yet eased. - [Charlie] And on May 18th, 1980, this lake was beneath several feet, perhaps as much as six feet of snow and three or four feet of ice. - [Narrator] That snow and
ice protected young trees which have now grown to be the largest things on the landscape, and it provided a thermal
buffer for life under the water. - [Charlie] Tens of thousands, perhaps hundreds of thousands, millions of individuals of most species survived somewhere in the blast area. - [Narrator] For amphibians,
15 species were known at Mount Saint Helens before the blast. 12 survive to this day. It includes the northwest salamander, which Crisafulli counts
and measures each year. - [Charlie] The difference is is all the animals we're
sampling now in this lake are the aquatic form. - [Narrator] Many northwest
salamanders grow up, go through metamorphosis by
losing their tails and gills, and then live on land. But for these, it's as if they know there's
not yet a real forest nearby to live in, so they've adapted. They live out their entire lives in water. - Now almost this entire lake
is suitable amphibian habitat. - [Narrator] It's one thing
to account for amphibians surviving farther from the crater itself, but they are back at Spirit Lake too. - [Charlie] And what we've seen has been absolutely astonishing. - [Narrator] How does a creature
as small as an amphibian even get to a lake that had
been decimated of all life? Crisafulli believes they walked. - [Charlie] I've found them over five kilometers away
from where we've marked them, so these animals get out and they move. - [Narrator] Charlie found
tree frogs on the move too, and a clue of how they
survived the journey across the hostile Pumice Plain. They borrowed gopher holes
to hide from the heat. - That's exactly right, and creates a stepping stone between suitable patches of
habitats that are developing, and so any amphibian we find out here on the Pumice Plain and Spirit Lake had to come from some
distant source population. So they had to disperse here. - [Narrator] Everywhere you look, the resurgence is remarkable. Frogs and toads were back at Spirit Lake within one year of the eruption. Salamanders reappeared within five years. Many of Spirit Lake's salamanders do go through metamorphosis,
able to live on land. They then wander, doomed to search for a forest
which does not yet exist. But with two strategies to stay alive, either in water or on land, the northwestern salamander may have helped ensure
its species very survival in the face of overwhelming disturbance. - Essentially, they can switch hit. Some proportion of the
population is in the water, some is on land, and as a consequence, they're able to spread the risk. - [Narrator] Some had predicted
even surviving amphibians would not last, especially since amphibians
are on such a decline in much of the Cascades. - And here we are 27 years later, and we've learned one thing for sure, is that the amphibians have done very well in the face of the 1980 eruption. - [Narrator] The succession of species, from bacteria to microbes
to plankton to plants and amphibians and fish, has woven from Mount Saint
Helens a new web of life. (birds chirping) And it has forced scientists to literally rewrite the books on what they thought they knew of ecology, natural catastrophe, and survival. - [Charlie] Mount Saint Helens has provided a context, or a backdrop, for us to look at the way
systems respond to disturbance better than any that we've had an
opportunity to study before.
