where groundwater is available and have
literally overshadowed slow-growing
conifers such as Douglas fir and western hemlock, Frenzen says. Only when
the fast-growing trees mature, die
and fall over — a process that will take
decades — can the suppressed conifers
rise to prominence, he adds.
Many factors have influenced the
rate at which plants repopulated the
landslide deposits. For example, plants
with seeds carried by wind or by highly
mobile creatures like birds moved into
the blast zone faster. And because most
plant species recolonized the blast
zone from its edges, slender swaths
of devastation such as the deposits
in the relatively narrow North Fork
Toutle River valley were colonized
sooner than broad areas like the pumice
plain near the base of the volcano.
Animal recovery on landslide
deposits has been slow as well. Field
surveys before the 1980 eruption noted
15 amphibian species in the area, says
Frenzen. The eruption wiped them all
out; scientists surveying one wetland site
on the avalanche debris didn’t spot any
amphibians at all until three years after
the eruption, when researchers found
two species: Bufo boreas, the western
toad, and Pseudacris regilla, the Pacific
tree frog. Even today, no more than a
handful of the region’s original amphib-
Even nine years after the eruption, vegetation—largely concentrated around
stream channels and seeps—covered only about 10 percent of the hummocky
landslide debris in the North Fork Toutle River valley.
ian species dwell on the landslide debris.
Creatures living in ice-capped lakes
at the time of the eruption had better
chances of survival, as did subterranean
creatures and small animals such as
pocket gophers. Many migratory creatures had yet to return to the area for
breeding or spawning season that year,
so they were never at risk.
And because the event occurred midmorning, fortune smiled on nocturnal
creatures, many of which had returned
to their daytime hideouts before the
mountain roared.
Today, some parts of the blast-scarred
region teem with the highly mobile
creatures that quickly recolonized the
transformed ecosystem. Killdeer and
red-winged blackbirds thrive along the
densely thicketed edges of lakes and
small ponds where beaver busily harvest
trees to build lodges and dams. Herds of
elk forage the open valleys, and hawks
dive-bomb for rodents alongside fish-snatching osprey.
The lateral blast damaged or destroyed
150,000 houses worth of timber. Note
people standing in left foreground.
Muddy waters
Yet ecological recovery along water-
ways with unstable channels has
been spotty. On some hillsides, fresh
wounds appear where massive slumps
of unconsolidated ash have spilled
from the mountain and wiped the slate
clean. These denuded areas, as well
as the immense amounts of ash and
sediment still slathering the region’s
floodplains, boost the amount of silt in
rivers and streams.
