- [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.