Life Returnsto MountSt. Helens
Oneyear after a major eruptionturnedmuch of the mountaininto an apparentgrave,
the slopesshowabundantsignsof resurrection
by Roger del Moral
Picking my way acrossa dry and proximity of Mount St. Helensto scibarren mudflow 5,000feet up on the entific centersprovidesa rare opporslopesof Mount St. Helenslast Sep- tunity to apply advancedmethodsin
tember, only four months after the comprehensive,
long-term studies of
eruptionthat devastated
the mountain how ecosystemsrecoverafter a major
and far from any visible vegetation, volcaniceruption.
I discoveredan isolated,yet active,
As an ecologistinterestedin comant nest. These ants, probably f'or- Ray Atk6son
mica subnuda, were at the top of a
food chain whoselowerlevels,hidden
in the mudflow, were unknown.Decomposing
organismsandliving plants
may have formed the base of the
chain,but withoutdisturbingthe nest,
I could not determinewhether soil
animalsor fungi were involved.Despite my curiosity,I decidedthat my
ignorancewaslessimportantthan the
existenceof this microcosmicecosystem in a veritable desert.The ants
wereaddingnutrientsto the mud and
hasteningthe reestablishment
of less
ad hoc food chains.After watchingthe
activities of these tiny survivors for
a while, I continued up the slope,
searchingfor signsof life among the
ruins of what was once the most perfect of the Cascadevolcanoes.
As Mount St. Helensmarksthe first Above:Residentsof Portland,
anniversaryof its May I 8, 1980,erup- Oregon,had a spectacularview of
tion, it has already been exposedto the July 22, 1980,eruptionof Mount
more hoursof scientificscrutinvthan St. Helens,one of severalsizable
most volcanoesare ever subjecledto. blasts that followed the major
Logistical and technical problems eruptionof May j,8.The mountain's
plagued efforts to study earlier erup- proximity to urban centershas been
tions of other North American vol- a boon to scientists.Right: Two
canoes.Mount Katmai in Alaska.for months after the May 18 eruption, a
example,eruptedin 1912,but ecolo- parsleyfern wasfound growing in a
gist R. F. Griggs (to whom scientists protectedarea along a creekon the
owe a major debt for his pioneering slope of the mountain. Thefern,
botanicaland geologicstudiesof that which surviveda small mudflow,is
volcano)was unableto approachthe growing out of a mud-covered
mountainuntil 1916.By contrast.the crevice.
petitionand succession
in stressfulenvironments,I found myself amongthe
hundredsof scientistsdrawn to the
mountain by the opportunity to document in detail the recovery process
and by the exciting chance to test
ecological,evolutionary,and biogeographical hypotheses.Biologistsobserving events as they unfold on
Mount St. Helens are asking many
questions:
Which speciesfirst colonize
the variouscompletelydestroyedhabitats? Are successionprocesseson totally denudedsitesfundamentallydifferent from processeson sites with
a residual biota? Does repeatedextinction and recolonizationresult in
populationsthat are geneticallydistinct from populationsof the same
speciesin stablehabitats?Might communitieswhosespeciesoccur in proportions different from the regional
norm be produOed?
My first field experienceon the volcano after the eruption was on a reconnaissance
trip last July with Jerry
Franklin of the U.S. Forest Service
and severalother biologists.While we
were awed by the magnitudeof the
destruction,I wasimpressed
eventhen
by the early evidenceof biologicalrecoYery.Sincethat time, I have made
several research trips into various
parts of the volcano's"red zone" (the
Forest Service'sdesignationfor the
potentially most dangerousland, to
which accessis closelycontrolled).I
havealsospokenwith manyother scientists investigatingresurrectionon
the mountain.The emergingpicture
is oneof diversity-diversityof impact
and, consequently,of the conditions
to which organismsmust adapt. AlRoger del Moral
36
titude and seasoninfluenced the nature and extentof the damagesuffered
by different parts of the mountain.
ln May, much of the landscapewas
still coveredwith snow.By contrast,
when I visitedthe volcanolate in the
summerof 1980 after a minor eruption, I found that hot-gas emissions
had scorchedexposedplants. These
witheredbits of straw providedan inkling of what might happenif a big
eruptionoccurredwhen there was no
snowpackto cushionthe blow.
The May 18 eruption, like subsequent smaller eruptions,was a series
of events, each producing different
conditions.In someplaces,biotic recovery has begun with survivors; in
others,colonizersfrom outsidethe impactedzoneare required.Many ecosystemswon't return to anything resembling their preeruption state for
years. But almost all affected ecosystems are showingresilience,and the
message
is clear:while it took a beating, life was never obliterated from
Mount St. Helens.
The eruption, which followed two
months of relatively minor volcanic
activity, unexpectedlyconcentrated
its force on the land to the north.
Although geologistshad anticipated
a major eruption and the magnitude
of the blast was not unprecedented,
no one was prepared for the degree
of devastation
spawnedby the unusual
lateraldirectionof the eruption.More
than a cubic mile of ash wasinjected
into the atmosphere,eventually coating hundredsof squaremilesof forest
and agriculturalland. Millions of insectswereknockeddeadfrom the sky.
Heat scorchedtreesup to sixteenmiles melting of ShoestringGlacier caused
north of the crater,and the blastblew a mudflow along Pine Creek that covdown trees in an arc of 160 degrees, ered vegetationon the edgesof the
extending more than ten miles from creekwhile removingit from the creek
the crater.In mostareaswithin a six- bed. In total, the eruptionof Mount
mile radius of the crater all life was St. Helenshad a profoundimpact on
destroyed. Large, rapid mudflows, a regionof about 160 squaremiles.
confinedto the lower elevationsof sevThe number of animals killed as
eral of the mountain'smajor stream a direct result of the explosionwas
systems,crestedover twenty-fivefeet high. Subterraneananimals,such as
and buried the flood plains of the pocket gophers,appear to have surMuddy River to the east and both vived in many placeseven within the
forks of the Toutle River to the west. blast zone, but mammals and birds
A flow of hot debris then swept all living aboveground had no protection
life from the northern flank of the from the blast. The Washington Demountainandthe upperToutleValley, partment of Game estimates that
creatingan eeriemoonscape.
(Unlike amongthe more prominent casualties
the sterile surface of the moon, how- were 5,200 elk, 6,000 black+ailed
ever, the debris is rich in organic re- deer, 200 black bears, 11,000hares,
siduals.)Melting glaciersand snow- l5 mountain lions, 300 bobcats,
fields triggered smaller mudflows on 27,000grouse,and 1,400coyotes;the
the upper slopes.For example,on the agencyhasestimatedheavyadditibnal
southeastflank of the mountain. the lossesdue to ashfall.The eruptionalso
38
severelydamagedtwenty-sixlakesbnd
killed someelevenmillion fish,including trout and young salmon.
Animals outsidethe blastedareas
must contend with altered habitats
and reducedquantitiesand quality of
food. [n the blowdownzone.elk and
deerare now commonnearwaterand
where fresh forage has emergedfrom
the ash. Thesesurvivorsmay have to
forage more widely, but their reduced
numbers will ease competition
stresses.Zoologistsexpect the populations of vertebratesto build up as
the vegetationrecovers,and they are
hoping to determine how much the
vertebrate pioneersmay changetheir
behavior with respect to habitat and
resource use as their numbers increase.Significant changesin behavior would constitute evidencefor interspecific competition, normally difficult to observein nature.
Far left: Twelve miles or so west of
Mount St. Helens (visible in the
distance),clear-cut andforested
areasalong the North Fork of the
Toutle River escapeddirect efects
ofthe eruption. Large, rapid
mudflows, however,buried the
river'sflood plain. Left: Closer to
the volcano,treeswereblown down
and a hot debrisflow, placed on top
of the mudflow, sweptall life from
the upper Toutle Valley.
Larger vertebratesmay form a cru- but unaffectedhabitats?Daniel Sim- usuallythe best able to disperse.Recial link in the processof vegetation berloff's experiments during the duced competition and the absence
recolonization.Where heavy ash or 1960s,in which all insectswere re- of predatorsin their new environment
mudflowsdried to form a hard, uni- moved from a series of very small may permit a "founder effect" to ocform crust. there are few cracks to Florida keys,indicatethat such com- cur, that is, the genetic differences
shelter germinatingseeds.But large munitieswill soonreturn to the same betweenfounding individuals and the
animalswanderingin searchof food number of speciesbut that the com- average members of the donor popor water make tracks that trap seeds position,largely a matter of chance, ulation become fixed. Such differand provide micrositessuitably miti- will be quite different.In the Mount enceswill probably be minor, but if
gated for germinationand growth.
St. Helens blast zone,the habitat is they occur repeatedlyin many species,
Insectssufferedincalculabletolls, larger than in the islandexperiments biogeographicalprocessesthat are
primarily from the ash effectsof the and there is no significantbarrier to known to operatebetweenislandswill
May 18 eruption and from sizable migration.Will this alter the results? have been shownto be significantfor
blaststhat occurredon May 25 and Will novel, stableassemblages
of in- evolutionary processesin terrestrial
June 12. Abrasionof the exoskeleton sectsbe formed?
situationsas well.
Food limitations present surviving
The effectsof the eruption on vegeand ingestionof ash during preening
were major causesof death. Studies insects and early immigrants with tation in various zonesare also under
of agriculturalareasin centralWash- unique challenges.Specieswith the study: In forests within a few miles
ington have revealedthat although most generalizedrequirementsare of the mountain, the initial ash dehoneybees
and otherbeneficialinsects predicted to be successful,and some posits fell wet becauseof eruptionsufferedgreatly, most insect popula- early observationsin the blowdown induced thunderstorms and covered
tions recovered quickly. Nearer area support the idea that survival the trees and ground with a thick goo,
Mount St. Helens,where higher al- requires adaptability. In the weeks which soon dried to form an impertitudes meana later spring,fewer in- after the big eruption, when ash was vious, cementlikelayer. Ash on vegesectswere exposedat the time of the ubiquitousand aphidswererare,Jerry tation interrupts gas exchange and
eruption.In the blowdownarea,many Franklin and I observeda ladybug, curtails photosynthesis.Jini Seymour
specieshave been encountered,but normally an aphid predator,feeding of the Universityof Washingtonmeaexceptnear water, their numbersare directly on the sap of a brackenfern suredtemperaturein ash-coatedsilver
reduced.I noted that seedset in lu- (Pteridium aquilinum) that had firs (Abies amabilis) and found them
pines,which are dependenton insects emerged from the ash. Such short- to be more than 30oF warmer than
for outcrossing(the productionof off- circuited food chainsshould return to adjacent leaves from which the ash
spring from individualsof the same normal as the vegetation,on which had been removed.Fortunately,since
speciesbut differentstrains),waspoor aphids and other herbivoresdepend, heavy ash fell prior to bud burst in
higher elevations,much ash-freenew
evenwherethe vegetationreceivedlit- recovers.
tle damage.I believethis poor seed
Becauseinsectshave short genera- growth is now presentin most of the
productionwasa resultof the relative tion times and are often early colo- surrounding forest. As ash-covered
paucity of pollinatinginsects.
nizers,entomologists
are likely to ob- leaves are washed clean by precipiInsect colonists will come from servemicroevolutionaryevents,which tation or replacedby new growth, co
poolsof insectsoutsidethe blastzone, involveshiftsin genefrequencyrather nifer prodirctivity shouldreturn to norand newinsectcommunitieswill even- than speciation.For example,where mal. Somespecies,suchas red cedar
tually develop.Will thesecommuni- biotic recoveryrequiresimmigration, (Thuja plicata), retain ash more teties be similar in speciesnumberand the first individuals of a speciesto naciouslythan others,suchas Douglas
compositionto communitiesin similar invade an area aie, not surprisingly, fir (Pseudotsuga menzdesii),but
Eyewitness accounts,photographs, and instrument
records have been used to piece together the initial
sequenceof the May 18, 1980,eruption of Mount St.
Helens, the youngest and most active Cascadevolcano.
A huge bulge formed rapidly, high on the north face of
the mountain's volcanic cone, in the weeksprior to May
18. Then, at 8:32 A.M. on that day, an earthquakestruck
the mountain, triggering an avalanche on the north face
that is now thought to be the largest ever witnessedby
humans. Superheated groundwater close to the magma
flashed into steam, resulting in a lateral explosion that
pulverized rock and trees and sent a hurricane-force,
hot-gas-propelled bolt of ash off the north face and
across the Toutle River Valley to the north and west.
Temperatures in this iderno were estimated to exceed
900" F. Comparable to a 400 megaton nuclear blast, the
explosion blew down trees in a l600 arc up to fourteen
miles north of the crater and totally devastateda
somewhat smaller "blast zone." Secondslater, overlying
rocks were incorporated into a high-velocity debris flow,
driven by rapidly melting glacial ice. On the western
flank of the mountain, this chocolate-coloredmass
swept down the upper Toutle River Valley, eventually
forming a mudfiow that swept the entire drainage area.
To the north, a lobe of this hot debris flow crashed into
Spirit Lake while another swept over 5)}-foot-high
T H EE R U P T I O N
.
')
i
I
:
,
i
l
BLASTZONE
TREEBLOWDOWN
MUDFLOW
L A N D S L I DAEN D D E B B I SF L O W
lii.trii$ PYROCLASTIC
FLOW
FLOOD
40
i :
ColdwaterRidge,removingall lrft in its*path.As the
summit of the mountaincollapsed,two verticalcolumns
of ash-ladengas and steam wereinjected more than
65,000feet into the air. This ash waseventually
deposited,in layers up to fve inchesthick, over 49
percentof lVashingtonState and beyond.Closeto the
mountain,ash depositswerelessthick, but theyfell wet,
forming o sticky goo on all surfaces.Theplume of
blastedash also removedmuch of the remainingsummit
and loweredthe peakfrom 9,677feet to about 8,400
thefeeding zoneof all glaciers
feet. As a consequence,
has disappeared.Shortly after theseeventsand
continuingthroughoutthe next day, an indeterminate
numberof pyroclasticflows, or nu6esardentes(hot,gaschargedavalanchesof fluidized rock fragments), were
ejectedfrom the crater, so that much of the upper debris
flow wascoveredwith more than seventyfeet of finely
powderedash and pumice.
The volcanoremainsactive,with frequentsmall,
harmonictremorsand occasionalburstsof steamand
ash.Sizableeruptions,with their attendantsmall
pyroclastic and pumiceflows, occuted on May 25, June
12, July 22, August 7, October17 and i,8,and December
27 of last year. Future eruptionsare expected,but most
geologistsbelievethat another large eruption is not
likely.
n
whethervariousspeciesof foresttrees were primarily subjectedto ash de- As succession
proceeds,
conditionswill
will show impo'rtant differences in positsare the scorchedconifersfound gradually alter in favor of species
mortality or productivity is not yet in a narrow but expandingband be- adapted to the forest. A major preclear.
tweengreentimber and standingdead diction to be testedduring the l98l
At higher elevations,snow pro- trees.Many treesin this borderzone, growingseasonis that within the blowtected the plants beneaththe canopy suchas westernhemlock(Tsuga het- down area,pioneerspeciesfrom clearof foresttreesfrom directashdeposits, erophylla), Douglasfir, and noble fir, cuts will make up the bulk of new
but impacts still accruedin this un- survivedthe initial surgeof heat and growth in the once forested parts.
derstoryvegetation.Many plant spe- gas from the main eruption but were However.sincethe flattenedtreescrecies already flattenedby snow were weakened by it and also received ate micrositesfavorableto the survival
trapped by heavy ash. Erosion and heavy ash deposits.During the dry and regenerationof some understory
rain may eventuallyremovesufficient summer, many trees gradually suc- vegetation,the next forest generation
ashto freesuchplants,but the damage cumbed from internal heat or other will be fosteredby the slowly decommay havebeentoo severeor too much factors. Fortunately, young saplings posingremainsof dead trees.
of the growingseason
may havepassed beneathmany of thesetreesescaped
The potentialjuxtapositionof plants
for them to survive. Mossesand li- virtually unscathedby virtue of the having markedly different ecological
chens,which form low mats, are the snowpackpresentduringthe eruption. strategiesoffers opportunitiesto test
mostseverelydamaged.Otherspecies, Thus, the next conifer generationis some ecological theories. Prevailing
such as the erect-growinghuckleber- already well establishedand should opinion would predict, for example,
ries (Vaccinium spp.), were able to experiencea burst of growthnow that that in openmicrosites,
pioneerspecies
emergefrom the ashlayerasthe snow the saplings are releasedfrom com- should outcompetethe forest species,
melted.Theseplantsgrewwell during petition with their parents.
whereasin protectedsites,the reverse
1980,probablybecausetherewasless
Still closer to the volcano.where shouldhappen.As conditionsimprove,
competitionfrom other plantsand be- standsof large trees did not survive overalldominanceshouldrestwith forcause the high insect mortality re- the first blast, stark contrastsappear est species.
ducedgrazingpressure.
Many of these betweenareas that had been clearThe region of tree blowdown and
emergentshavesentrootsinto the nu- cut shortly before the eruption and its surroundingring of moribundtrees
trient-rich ash and may thus benefit areasthat had beencoveredwith for- presentsthe U.S. ForestServicewith
directly from improvednutrition.
est. In most parts of the blowdown difficult managementoptions.StandJim MacMahonof Utah StateUni- area, snow again offered some pro- ing deadand downedtreesameliorate
versityhasshownthat pocketgophers tectionto ground-layer
vegetation,
and the microclimateof the substrate,reare major agentsof ashJayerdisrup- terrain closest to the mountain re- tard erosion. and foster natural suction. These little burrowing rodents ceivedlessashthan moredistantareas cession.Treesblown into streamchanimprove soil aeration and water in- directly in the path of fallout. In the nels reduceerosionand siltation and
filtration.As a consequence,
minerals clear-cut areas,regenerationof her- promote the recovery of streamside
from ash are more rapidly incorpo- baceousvegetationbeganshortlyafter vegetationand fauna. Furthermore,
rated into the soil, where they can the eruption.Speciesthat commonly there is a widespreaddesire to prebe usedby plants.Silviculturistsnor- grow on recent clear-cuts,such as serve much of this region for intermally view pocketgophersas unmiti- fireweed (Epilobium angustifolium), pretive, recreational,and scientific
gated pests becausethey eat young pearlyeverlasting(Anaphali s margar- purposes.The Forest Service,which
conifers,but for the next few years, itacea), and bracken fern, have eco- managesmost of the affected land,
gophersmay prove valuableallies in logical characteristicsdistinct from must reconcile these factors with the
the reestablishment
of tree seedlings thoseof forestunderstories.
Theygrow value of downedtimber and the danin clear-cutsand blowdownareas.
fast, produce many easily dispersed ger of fire or of beetle infestations
For most plant species,recoveryin seeds,and are able to colonizenewly in Douglas fir, starting in moribund
heavily ashed areas will be rapid. disturbedsitesrapidly,toleratinghigh vegetationand moving into healthy,
Young Douglas firs, silver firs, and light, high temperatures,
and drought. economically
valuableforests.Salvage
noble firs (Abies procera) may suffer
In contrast,areasin the blowdown removal of downedtimber is beginheavy mortality, and speciesof li- region that were coveredby deepfor- ning,althoughnot in areasdesignated
chens,mosses,and other low-growing est at the time of the eruption lacked for detailedstudy by the ForestSerplants will be disproportionately
rare herbaceousvegetation as snows re- vice SpecialPlanningTeam.
for manyyears,but overallforestpro- turnedin the winter of 1980.The forFloodplainsare intrinsicallyunstaductivity should soon return to pre- est understory normally consistsof ble habitats, and those in the area
eruption levels.When nutrientsfrom herbs and shrub speciesadaptedto affectedby the May 18 eruptionwill
the ash, such as phosphorusand po- cool, moist, dark conditions.These recovermore slowly than either the
tassium,are added to the soil, they grow slowly; produce few, poorly dis- ashor blowdownzones.The mudflows,
may actually generatea pulse of en- persed seeds;and are intolerant of which sweptthe lowerthirty-twomiles
hanced productivity. Understanding high-lightor high-temperature
condi- of the North Fork of the Toutle River,
the differentialeffectsof Mount St. tions.Any suchunderstoryplantsthat fifteen miles of the Muddy River, and
Helens'ashdepositson vegetationwill survived the adverseimpact of the many smallerstreams,removedmost
improve the ability of ecologiststo blast and ash layers were thus con- of the vegetationin their path before
readthe historyencodedin tree rings, frontedwith an inimical environment. settlinginto unstablemasses.Erosion
pollen records, and soil profiles in
Recoveryin theseblowdownareas rateswill be high, and successful
seed
other volcano-dominated
ecosystems. will requireinvasionby aggressive
spO- invasion will be limited for many
Lessapt to survivethan treesthat cies from the surroundingclear-cuts. years.Last July I observed
cottonwood
4l
OouglasC. Anderson
of the hypot-hesisthat the recovery
rate on a site from which vegetation
has been totally obliterateddepends
on the proximityto a poolof colonists.
According to this hypothesis,recovery
shouldproceedmuch morerapidly on
the South Fork than on the North
Fork.
Experimental manipulationsof
plots establishedon the debris flows
duringthe nextseveralyearsmay also
help answersome general questions
about succession.
Is there a definitive
sequenceto the recoverypattern or
do chanceand local seedavailability
dominatethe process?
Are the activitiesof specificcolonizingplant species
requiredto facilitate the subsequent
successof other species?
One way to
testsuchhypotheses
is by determining
whether,after a numberof years,plots
In many places, trees that withstood
the blast were scorched by heat and
noxious gases and covered with ash.
Where this occurred. the mountain
shows a line between brown. deqd
trees and green, living ones.
(Populustrichocarpa)seedlingscolonizing the lower North Fork of the
Toutle.Becausethey floatthroughthe
air, cottonwoodseedswereamongthe
few seedsavailableshortly after the
May eruption. Unfortunately,subsequent erosionfrom minor summer
rains washed these seedlingsaway.
Bob Zasoski of the University of
Washingtonhas estimatedthat more
than ten years will pass before the
first trees are establishedon these
mudflowsand more than a century
before a more or less normal forest
can develop.
While mudflows devastatedthe
lower river valleys,a hugedebrisflow
-a turbulent,water-driven,hot mass
of rocks,boulders,and uprootedtrees
-ravaged the uppervalleyof the Toutle's North Fork. A few plants miraculouslysurvivedthe vast jumble,
and an occasional
fireweedor bracken
fern rhizome sprouted,but recovery
on this debris flow will dependprimarily on seedsinvading from less
damagedareas.
Comparisons
betweenthe broaddebris flow on the North Fork of the
Toutle River and the much narrower
mudflow, close to intact vegetation,
on the South Fork will providea test
A 1
from which the first cr:lgnistsare periodicallyremoveddiffer from control
plots. Another questionof interestis
whethersuccession
tendsto converge
toward a single community type or
whetherinitial site differencespersist
indefinitely.This questionmay be answeredby comparingthe initial degree
of vegetationheterogeneitywith that
found five or ten yearslater. Significantly reduced variety would imply
that convergence
is indeedoccurring.
Severalslowerand lesspublicized
mudflows were driven by glaciers
melting on the east,south,and west
slopesof Mount St. Helens.Last September, I visited the upper portion
of the six-mile-longPine Creek mudflow, which was propelledby the now
nearly defunct ShoestringGlacier on
the southeastflank of the volcano.
Although the preeruptionvegetation (Polygonum newberryi), did not
in this locationis not known,the area emergeuntil light rainscreatedsmall
still revealsinterestingaspectsof vege- erosion channelsalong which these
tation recovery.The heat and toxic plantswereconfined.Wheremud was
fumesof the main eruptionkilled the morethan abouta fooddeep,no vegesparselodgepolepine(Pinuscontorta) tation emergedin 1980.
and subalpinefir (Abies lasiocarpa) Since mud seali the soil and can
scatteredon the high ridges above limit oxygen exchange,buried vegePine Creek.The subsequent
mudflow tation may be suppressed
throughthe
destroyedcreek vegetation but it inhibition of root respiration.An almerely buried the snow-covered
dor- ternative mechanism,however,may
mant ground cover of the ridge. Ini- operateon mudflowsand in areasof
tially there was no vegetationon the heavy ash deposition.Both mud and
mudflow. which varied in thickness ashinsulatethe soil and createa light
from a few inches near the treeline barrier.twocharacteristics
of a snowto more than five feet at its upper pack. Many plant specieshere and
end. The Cascade aster (Aster led- elsewheremay be fooled into "thinkophyllus)wasthe first plant to emerge ing" that winter continues.If this is
through this mud. Other herbs, in- so, as the 1980/81winter snowpack
cludingthe broadlupine(Lupinuslat- meltsand further erosioncleanses
the
ifulius) and Newberry's knotweed mountain, surviving vegetationwill
emerge,havingmisseda growingseason but otherwiseunscathed.
North of Pine Creek lies Abraham
Plains, a site that supportedonly
limited vegetationprior to the May
1980eruption.After the initial eruption, pyroclastic and hot-ash flows
melted snowfieldson the mountain's
northeastern
flank.The resultantmudflows coveredor removed all vegetation on these plains. Revegetation
in this area, unlike Pine Creek, will
thus dependentirely on seed immigration.
The differencesbetweenrecoverv
due completelyto immigration and
that abetted by residual vegetation
will be documentedin permanently
markedplots at Abraham Plainsand
Pine Creek. Questionsabout succession under stressfulconditionswill be
addressed.Do survivors and immigrantsbelongto the samespecies?
Or,
as in the caseof Abraham Plains,is
the habitatso severethat pioneersare
the only speciescapableof survival?
Are differencesin speciescomposition
due to dispersalfailuresor simply to
the absentspecies'inability to grow
in unalteredmudflow material?Answersto suchquestionscan be applied
to the future reclamationof derelict
Soon after the eruption, herbaceous
vegetationbeganreturning to recent
clear-cutswithin the blast zone.
The pink flowers of fireweed, a
colonizing speciesof disturbed
areas, were a common sight.
43
In what was oncea large meadow
coveredwith hucklebeny bushes,a
lone spottedfrog, right, rests next to
a dying bush. To support this
amphibian,the meadowmust still
havesomepermanentwater source.
Mammals, birds, and insectshave
left recordsof their wanderingsin
the ash and mud, below. llthere the
crust is hard, the tracks of large
animals provide trapsfor seedsand
suitable sitesfor germination.
landsin volcanic.regions-of
the Pacific lost most of their vegetation. NorNorthwest.
mally,thesevalleyssupportplantsdifFurther insightinto recoverymech- ferent from thoseon the more exposed
anismswill' come from observations ridges, but ridge vegetationis now
of revegetationin siteson the periph- the most likely source of seeds for
ery of the directedblast. The ridges the newly exposedterrain. Mountain
and glacial valleysin theseareases- glacierssuchas the onesthat formed
capedthe debrisflow and pyroclastic thesevalleys ordinarily retreat slowly
activity. On ridges above the South enough for valley vegetationto keep
Fork of the ToutleRiver,for example, pace.When Mount St. Helenserupthe few lodgepolepinesat timberline ted, however,the rapid melting of the
werekilled by the scorchingblast,but glaciersnot only exposedlarge areas
the lush herbaceousvegetationthat for the first time in more than a cennormally dominatestheseridges,in- tury but also washedaway most vegcluding the yellow penstemon(Pen- etationbelowthe glacier.Thus,in the
stemonconfertus)and the broadleaf absenceof speciesspecificallyadapted
lupine,.returnedwith no apparentill to the valleys,ridge speciesmay exeffects.On the other hand,the glacial pand their habitat and create novel
valleysbelowthe ridges,scorchedby assemblages
in the valleys.
the directedblast or scouredby mudMount St. Helensis so young and
flowsresultingfrom melting glaciers, its environmentso harshthat evenunder normal conditionsonly the more
generalizedand stress-tolerant
plants
can survive.All plantscommonto the
upperslopesdisplayadaptationto unstable or chronicallydisturbedenvironments:deeptaproots,buriedgrowing points, large storagereserves,and
good dispersal mechanisms.Therefore, although ridge-dwellingplants
may under normal circumstancesbe
competitivelyinferior to valley dwellers, they may be physiologicallycapable of surviving in the valleys. I
plan to monitor the developmentof
the upper glaciervalley vegetationto
see whether plant communitiescomposed of ridge speciesdo develop.
Their existencein the valleyswould
be strong,althoughindirect,evidence
for the importanceof competitionin
stressfulenvironments.
Of all the regions on the mountain, the most severelyaffectedwas
the blast zone immediatelynorth of
the crater, includingSpirit Lake. Every type of volcanic behavior displayed by the mountainhas assailed
this terrain. All life was seemingly
obliterated.Treeswerepulverizedand
soil vaporized.Yet, evenhere, life is
returning.Forestrecoverywill be slow,
but it will happen.Soil development
will requirethe establishment
of mushrooms,Iichens,and pioneeringherbs.
Seedand sporesourcesare scarcebut
a few pockets of vegetation remain.
A protected ridge beyond Abraham
Plains, on the easternedge of this
area,for example,supportssomesilver
firs and a few areas of herbaceous
vegetation.
Higher terrestriallife may be scarce
in the blast zone but dead organic
matter is abundant,and such a re-
source is never unexploited for long.
Here, where many humans died,
where entire ecosystemsceasedto exist in a matter of seconds,Dave Hosford of Central WashingtonState College has found a mushroom,Autracobia melaloma, growing from the
ash, slowly decomposingorganic matter found there, and beginninga terrestrial succession.
Most of the biologicalactionin the
blast zone, however,is taking place
in lakes.Spirit Lake, once a pristine
and clear body of water and now as
appealingas a sewagelagoon,teems
with microscopiclife. Bob Wissmar
of the Universityof Washington,who
is conductinga systematicsurveyof
the affected lakes, has pointed out
that the water in Spirit Lake was totally removedby the force of the debris flow and replacedby a hot, muddy
slurry of ash and debris. Thousands
of trees, blown off the mountain and
washedinto the lake, have provided
the basisof a new aquaticfood chain
on the cloggedwater surface.As the
water cooled, blue-greenalgae and
bacteria were the first active organisms,but decomposing
anaerobicbacteriaand protozoans
nowdominatethe
biota. The slowly dissolvingorganic
matter hasreducedthe oxygencontent
of the lake and continuesto release
prodigiousquantitiesof sulfurdioxide,
the smell of which permeatesthe pyroclasticzone.
Many yearswill passbeforeSpirit
Lake and other profoundly altered
'their
lakes return to a semblanceof
preeruptivestate. Recoverywill be
faster in smaller,higher lakes,which
were more thoroughly protected by
the snowpack.Higher lakes not hit
by debris flows or mudflowswere primarily affected by ash fallout and receivedonly limited amountsof organic
matter.
Ephemerallakes,ladenwith organic
debris and silt, pockmarkthe debris
flow that settled into the North Fork
of the Toutle River. Theselakeswere
quite warm throughoutlast summer,
and decomposition
in them was rampant.A witch'sbrewof phenolicacids
and tannins,smellingstronglyof creosote and turpentine,is still draining
from them. Tracks of elk, deer, and
coyote are frequently encounteredon
the debris flow where little food is
evident,suggestingthat the animals
may well be in searchof water. Unfortunately,the quality of the water
in ephemeraland permanentlakesis
suspect,On'one occasion,I found a
deaddeermouse,apparentlypoisoned
by the tannin-blackened
waterin Castle Lake,which formedwhenthe May
eruptiondammedCastle Creek.
As I write, the winter rainscleanse
the forest of ash. and snow falls on
the mountain slopes, restoring to
Mount St. Helens a pristine appearance. The volcano will undoubtedly
rumblefor severalyears,however,and
minor damageis likely to continue,
particularlyon the northslope.In such
areas, the biological recovery clock
may restart severaltimes, providing
future opportunitiesto observeseveral
stagesof succession
simultaneously.
Recoveryon the mountainwill go
on for many years.At first, physical
changeswill predominate:
wind will
removethe dust, mud will erode,glaciers may recover somewhat.Many
lakes and streams should recover
quickly, althoughthe persistence
of
heavy sediment loads will probably
retard the recovery of fish. In the
higher forests,snow-protectedsmall
trees will form the next generation
and providea forestedlook to much
of the blowdownarea within fifteen
to twenty-fiveyears. Above timberline, as survivingvegetationemerges
from beneathmudflowsand ash.onlv
subtle differencesfrom preeruption
conditionswill be evident. Where
high-elevationvegetationwas destroyed,however,revegetation
will be
slow and dependenton long-distance
dispersal.
Foresters,ecologists,soil scientists,
limnblogists,entomologists,
and other
biologistshavecoordinatedtheir studies of the biologicalaftermathof the
1980 Mount St. Helenseruptions.In
our effortsto understandhow ecosystems recoverfrom such fundamental
disturbances,
we build on the work
of pioneers.What we learn may, in
turn, help us developjudicious ways
to cope with future natural catastrophes.No onewishesto experience
further Cascadeeruptions,but should
they happen,we will be better preparedto encourage
rapid and effective
ecosystemrecoverytechniques. n
llith the afternoonsun obscured
behind a ridge,fireweed blossoms
scattertheir luminousmessage
of
life among the stumps of an earlier
clear-cutoperationfour miles west
of the peak of Mount St. Helens.
Ralph Perry
46