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TRANSCRIPT
A PRELIMINARY REPORT OF AIRBORNE STUDIES BY THEUNIVERSITY OF WASHINGTON OF THE EFFLUENTS FROM THE
MT. ST. HELENS VOLCANIC ERUPTIONS
by
Peter V. Hobbs, Lawrence F. Radke, Mark W. Eitgroth and Dean A. HeggCloud and Aerosol Research GroupAtmospheric Sciences Department
University of Washington, Seattle. WA 981 95
June 12, 1980
A PRELIMINARY REPORT OF AIRBORNE STUDIES BY THEUNIVERSITY OF WASHINGTON OF THE EFFLUENTS FROM T;;L
MT. ST. HELENS VOLCANIC ERUPTIONS*
by
Peter V. Hobbs, Lawrence F. Radke, Mark W. Eitgroth and Dean A. HeggCloud and Aerosol Research GroupAtmospheric Sciences Department
University of Washington, Seattle, WA 98195
Introduction
Mt. St. Helens ended its 123 year of dormancy on March 20, 1980 with a
single small quake registering 4. 1 on the Richter scale. Seismic activity
increased steadily, becoming nearly continuous by March 25. The first eruption
occurred on March 27 at 1236 Pacific Standard Time (PST) when a thick dark pl ume
of ash was reported reaching 16,000 ft. The University of Washington’s (UW)
Cloud and Aerosol Research Group began regular airborne observations and
measurements of the volcanic effluents on March 28.
In view of the considerable interest in the nature of the emissions from Mt.
St. Helens, we provide here a short prel iminary overview of our airborne
measurements to date. These airborne measurements are continuing, with one
fl ight a week when volcanic activity is low and more numerous fl ights when the
activity increases. A fu1 1 scientific report of our studies wil l be publ ished
n due course.
* Before using or quoting in publ ications or reports any of the scientificresults reported herein, written permission must be obtained from ProfessorHobbs.
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Instrumentation
Measurements made aboard the UW’s B-23 research aircraft are isted in Table
1. As can be seen, the instrumentation permits comprehensive measurements of
the sizes, concentrations and nature of airborne particles over the size
range ~0.01um 4.5mm, and of the nature and concentrations of a large number
of trace gases.
Measurement Procedures
Each fl ight commences in the vicinity of Mt. St. Helens and continues with
measurements at increasing distances downwind in the pl ume of the effluents from
the volcano. The altitudes of the fl ight paths range from about 4000 to 18,000
ft.
Measurements of the size spectra of particl es, filter samples for chemical
and optical analyzes, and gaseous measurements are obtained by feeding "grab"
samples of air through the appropriate instruments and devices aboard the
aircraft (concentrations of sulfur, nitrogen oxide and ozone are measured
continuously). The "grab" sampl es of air (volcanic pl ume or ambient) are
collected in a large (150 gal on) myl ar bag and/or stainl ess steel cannisters in
5 seconds. The "grab" sample technique is desirable for two reasons. Firstly,
it permits col ection of sufficient sampl es of effluent for subsequent measure-
ments without requiring the aircraft to be flying within the volcanic pl ume for
long periods of time (this is necessary, for safety reasons, when the pl ume is
very thick). Secondly, it al lows acquisition of a series of essentially point
sampl es, and each set of measurements is made on the same point sampl e.
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TABLE 1. SPECIFICATIONS OF RESEARCH INSTRUMENTS ABOARD THE UNIVERSITY OFWASHINGTON’S B-23 AIRCRAFT USED IN THIS STUDY.
Parameter Instrument type Range Principal Investigators
Size spectrum ofaerosol particles
Size spectrum ofaerosol particl es
Size spectrum ofaerosol particl es
Size spectrum ofaerosol particles
Size spectrum ofaerosol andcloud particl es
Size spectrum of cloudparticles and largeash particl es
Size spectrum of pre-cipitation particl esand large ash particl es
Concentrations ofAitken nucl ei
Images of cl oud^articles and largeash particl es
Images of precipitaionparticl es and largeash particl es
Sizes and types ofaerosol particl es
Mass concentrationof aerosol particles
"articul ate sul fur
Electrical mobil ityanalyzer
90 l ight scattering
Forward1 ight-scattering
Diffusion battery
Forward1 ight-scattering
Diode occulation
Diode occul ation
Rapid expansion andl ight transmission
Diode occul ation
Diode occulation
Direct impaction
0.0032 to 1.0 vm
0.3 to 12 urn
1.5 to 40 vm
0.01 0.2 pm
1.5 to 70 urn
20 to 300 pm
300 to 4500 urn
10 to 106 cm-3
25 to 1000 urn
100 to 5000 urn
5 to 100 urn
Profs. P. V. Hobbsand L. F. Radke
El ectrostatic deposition 0.1 to 3000 ug m-3onto matched oscil ators
Pali fl ex filters 0. 1 to 50 pg m-3(then flash volatil ization)
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TABLE 1 (CONTINUED)
Parameter Instrument type Range Princi pal Investigators
Chemical constituentsof particul ates (S04=,NOT, C1 -, Br-, Na^Ca^, NH4-1-, K’1’, P04",F-, etc. )
El ectric field
Space charge
Photographs
Total gaseous sulfur(sequential scrubbersal low separation ofSOx, H^S, inertgaseous species)
NO, N02, NOx(NH3 occasional ly)
Light-scatteringcoefficient
Windspeed andduration
"Inert" gaseousspecies (e.g. COS,CO, C02. CH4, CS2,t^O, CH3C1 andhalocarbons)
Identification ofel ements n sizesegregated aerosolparticl es
Ion exchange chromatograph Variable(sol ution extracted from ^in-8 ^i
tefl on filters) >10 mol ar
Profs. P. V. Hobbsand L. F. Radke
Field mill
Conductivity meter
35mm time-lapse camera
Flamephotometric detector
Chemil uminescence (03)
Integrating nephel ometer
Doppler navigator
+ 0 to 100 kV
2 x 10-9 10-15 A
1 s to 10 min
0 to 10 ppm
0 to 5 ppm
0 to 2.5 x 10-4 m-1or0 to 10 x 10-4 m-1
0 to 360,0 to 100 m s-1
"Grab" samples with post Variabl efl ight analysis withmultiple col umn gas chrom-atograph, mass spectrometer,and flame ionization detection
Lundgren impactor (computer Variablecontrol l ed). Analyzed byPIXE (18 MeV a particl es)
Prof. D. CronnWashington StateUniversity, WA
Prof. T. CahillUniversity ofCal ifornia at Davis CA
Inert" gases (e.g.02, Ar, N2, CO, C02,He, H2, CH4, C2He,H2S)
Radon Gas
Optical Absorptionof Particl es
Cascade impactor from Variabl e"grab" sampl e. PIXE analysis(5 MeV protons)
Gas chromatograph Variabl e(with thermal conditionerdetector)
"Grab" sample Unknown
Integrating pl ate Unknown
Dr. A. Lesl ieFl orida StateUniversity, FL
Dr. W. EvansUSGS. Meni o Park, CA
Dr. D. Dougl asEPA, Las Vegas, NV
J. Ogren (U.W.
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Overview of Observations and Measurements
A very brief summary of the observations and measurements obtai ned on the
sixteen fl ights that we have made to date is given in Table 2. A few further
comments, and illustrations of some of the measurements obtained, wil l suffice
to complete this prel iminary report.
The emissions encountered on our first fl ight over Mt. St. Helens on March
28, 1980, were impressive (but fairly small compared to the emissions from the
St. Augustine volcanic eruptions which we studied in 1976*). The size spectra
of particl es measured in the effluents from the volcano at 7 nautical miles
downwind on March 28 are shown in Fig. 1. It, can be seen that the concen-
trations of particles from ~1-10 un, measured in a puff of ash, were up to a
factor of 1000 greater than in the ambient air, but for particl es <lum the con-
centrations were simil ar to those in the ambient air. The mass concentration of
particles less than 2 urn in size in this cl oud of ash and in the ambient air were
3~660 and 30 vg m respectively. The concentrations of total sul fur gases in
the pl ume reached val ues of 240 ppb and consisted mostly of hydrogen sul fide.
Between March 28 and May 17, when the volcanic activity was fl uctuating,
seven further fl ights were made (see Table 2) On April 2, April 4, April 8 and
April 11 the total sul fur concentrations were in the range 15-38 ppb with
fluctuations in the hLS and SO., components. On May 8 however the total sul fur
"Airborne Particl e and Gas Measurements in the Emissions from Six Volcanoes"by J. L. Stith, P. V. Hobbs and L. F. Radke, J. Geophysical Research, 8J3,4009-4017 (1978).
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TABLE 2. CHRONOLOGY OF THE ACTIVITY OF MT. ST. HELENSAND UNIVERSITY OF WASHINGTON RESEARCH FLIGHTS
Date (1980) Fl ight(times inPST to
nearest hr’’
Comments
March 20
March 25
March 27
March 28 1
First
Intens
First
Second
earth
e sei
erupt
erup
quak
smic
ion.
tion
e.
a;cti
Ash
As
vit
Pi
h p
ity.
ume rep
ilumes u
orted to 16,000
p to 20,000 ft.
ft.
DurationSecond eruption. Ash plumes up to 20,000 ft. Durationof ash eruptions 5-10 min with more frequent andshorter steam explosions. Aircraft fol lowed one ashburst 55 miles east (minor activity compared to the1976 eruptions of St. Augustine, Alaska). Total sul furgases up to 240 ppb mainly H^S.
March 30-April 1
April 2 2(1000-1400)
April 4 3(1200-1500)
April 8 4(1300-1500)
Infrequent ash eruptions.
Brief ash and steam explosions.COg concentrations in the ash pl ume ranged from 360-411ppm compared to ambient level s of 320 ppm.
Sampled moderate vol umes of ash which was rather cool(ash decended rapidly after emission). Sl ight H^Semissions. First fl ight on which significant con-centrations. of S04=, C1 and F~ were detected. Sampl edash (mostly old l ithic material with some freshlyfractured silaceous material
Frequent minor ash eruptions and steam explosions.First significant concentrations of SO^ measured (sinceMarch 28 eruption).
April 8-April 10
April 11 5(1200-1400)
April 12-April 22
April 23 6(1000-1300)
April 24-May 6
Bul ge on upper north fl ank of mountainMinor activity.confirmed.
Geyser-type steam explosion with water in craterdraining into vent and then exploding up to ~500 ftabove mountain top. Mi nor sul fur gas emissions (~50%S02).
Activity continued to decl ine
Lowest level of activity observed on fl ights so far.Very sl ight particle and gas emissions.
Activity continued to decl ine.
Al l times in this report are given as Pacific Standard Time (PST). AfterApril 27, local time is obtained by adding hour to the stated PST times.
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TABLE 2. (CONTINUED)
Date (1980) Fl ight(times inPST to
_______nearest hr)
Comments
May 7
May 8
May 8
May 9-May 16
May 17
May 18
7-8(1000-1300)
(1400-1600)
9 & 10(1000-1500)(1600-2000)
May 19 11(1100-1400)
May 20-May 22
May 23 12 & 13(0800-1200)(1300-1400)
May 25 14(0800-1300)
Ash and steam eruptions resumed.
Ash and steam eruptions sampl ed from ai rcraft (somewhatsmal ler than those of April 2).
Sul fur gas emissions back to several hundred partsper bill ion (ppb) with mostly H;?S but occasional lysignificant SO^* Peak altitude of eruptions ~13,000ft. MSL.
Ash and steam eruptions continued with decreasingfrequency.
Activity nearly ceased.
First major explosive eruption at 0732 PST. North faceof mountain col apsed. Many hot aval anches (nueeardentes). Eruptions reported to reach altitudes inexcess of 60,000 ft. UW fl ight out to ranges of 240nautical mil es downwind. Sul fur gas emissions very low(near ambient level s) except in a singl e area near thetop of the pl ume late in the day when 1 part per mil ion(ppm) of H2S was measured. High particl e mass loadingsmeasured throughout both fl ights.
Eruptions continued with heavy ash deposition to theeast but at a much reduced rate. H2S emissions high inmost sampl es (~0.5 ppm). SO^ concentratons in pl umenear ambient.
Eruption activity continued but at much reduced rates.
Measurements simil ar to May 19 but quantity of ash muchreduced. Airborne measurements extended to EasternWashington with emphasis on measurements of particl esresuspended (bl own up) from ground. Visibil ity verypoor in bl owing ash.
Second major expl osive eruption. Ash reported to al ti-tudes of ~40,000 ft. Ash deposited in WesternWashington and Oregon (Portl and). Airborne sampl esconsisted mainly of old l ithic silaci ous rock with nofresh gl assy material s. Some elevated C1 (HC1 ?).Gaseous sul fur generally less than 100 ppb and mostlyH2S.
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TABLE 2. (CONTINUED)
Date (1980) Fl ight(times inPST to
_______nearest hr)
Comments
May 26- Decl ining volcanic activity. Amonts of ash in eachMay 29 explosive pul se al so less.
May 30 15 Heavy steaming and very light ash to 11 ,000 ft.(0900-1300) Incandescent lava reported in crater but discounted by
our observations. Sulfur gas ~0.5 ppm (mostly H^S).
May 31- Activity simil ar to May 30.June 3
June 4 16 Visually similar activity to May 30 but sul fur gas con-(1000-1300) tained 30% SO^ with observations of SO^ up to 200 ppb
(the highest yet observed). Particles in airborneeffl uents rich in C1 ~, F~, Br- and 504s.
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Particle size distributions at 10,000 ft altitude and 7nautical miles downwind of Ht. St. Helens at 143 PST onMarch 28, 1980: (a) in the emitted ash (solid line) and(b) in the ambient air (dashed line)
lO-^- 10-’ 10 10’ 102PARTICLE DIAMETER D (^m)
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concentrations had returned to val ues simil ar to those treasured on March 28
with 230 ppb of H2S and 53 ppb of SO^.
By May 18, seismic and visible activity had virtual ly ceased when, without
warning, a major eruption occurred at 0732 PST*. The north face of the mountain
collapsed in avalanches and pyroclastic flows, devastating a wide area north and
east of the mountain. The explosive eruptions ejected material to an altitude
of over 60,000 ft. and ash was carried eastward over Washington, Idaho and
Montana within a few hours (Fig. 2).
The UM research aircraft was in the air in the vicinity of Mt. St. Hel ens by
~1100 PST on May 18. The dark black cloud of ash over and downwind of Mt. St.
Helens was the largest we have seen in al l of our volcanic studies and was much
too thick to penetrate. However, measurements were obtained at the peripheral
edges of this ash cl oud using the "grab" sampl e technique. Shown in Fig. 3 is
one set of measurements of particl e size spectra obtained at a distance of 5
nautical miles downwind of Mt. St. Hel ens about 4l/2 hours after the start of the
major eruption. It can be seen that the concentrations of particles in the ash
cl oud varied from about a factor of 4 to over 1000 times greater than in the
ambient ai r. For particl es less than 2 urn in diameter, the mass loading in the
periphery of the ash cl oud was ~93 pg m whil e in the ambient air it was <0. 1
ug m~ The concentrations of sul fur gases, nitrogen oxides and ozone measured
in the periphery of the ash cl oud were not significantly different from the con-
centrations in the ambient air.
* 0832 local time.
Spread of the emissions from the expolsive eruption ofMt. St. Helens on May 18, 1980, as deduced from satelliteobservations. (Note: local time is obtained by adding1 hour to the PST times shown. )
lOOn.mi.
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!0-2 10-’ 10 10’
PARTICLE DIAMETER D (^ m)
Particle size distributions at 9700 ft attitude and 5nautical miles downwind at 1209-1227 on May 18, 1980:(a) at the periphery of the main ash cloud (solid line)and (b) in the ambient air (dashed line)
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In addition to the very black ash cloud, small er outlying "whitish" looki ng
clouds of effl uents were observed on May 18. These clouds were sufficiently
smal l that they could be penetrated completely by the UM aircraft and measure-
ments obtained in thei r interiors. Particl e size measurements obtained in such
a cloud are shown in Fig. 4. It can be seen that the concentrations of par-
ticles less than about 0.1 \im were no higher in these cl ouds than in the ambient
air, but for particles from about 0. 1 to 30 pm the concentrations were up to 100
times greater than in the ambient air. The mass concentrations of particles
l ess than 2 urn in the "whitish" clouds and in the ambient air were about 31 and
5.5 pg m~ respectively. The concentration of sulfur gases in these clouds was
at least 13 ppb (compared to ambient concentrations of 6 ppb) and was primarily
SO?. Nitrogen oxide and ozone concentrations in the "whitish" clouds were simi-
l ar to those in the ambient air.
Late in the evening, as the volcanic activity decl ined, our final measure-
ments were taken near the top (17,000 ft) of the main visibl e plume from the
volcano. These sampl es proved very rich in sulfur gas, about 1 ppm of mostly
hydrogen sul fide.
Another fl ight was carried out the fol lowing day (May 19) Emissions were
stil considerable, but much less than on May 18. Particle concentrations
measured in the peri phery of the main ash pl ume and in the ambient air, 12
nautical miles downwind of Mt. St. Helens are compared in Fig. 5. At this
range, mass loadings for particl es less than 2 urn in the pl ume and in the
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04
0’
02
111.1,. //Whi teeffluentclouds-^
0
0 o
Ambientair---
10-’
10-2
0-3
10-4^10-3 0 -2 10 -’ 10 0’ 10
PARTICLE DIAMETER D (^. m)
2
Particle size distributions at 10,500 ft altitude and 70nautical miles downwind at 1830 18&? PST on ’lay 181980: (a) in the "whitish" effluent clouds (solid line)and (b) in the ambient air (dashed line)
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10-3 10-2 10-’ 10 10 102PARTICLE DIAMETER D (^m)
Particle size distribution at 8900 ft altitude and 12nautical miles downwind of Mt. St. Helens at 1338-1340 PSTon Y-ay 19,. 1980: (a) on the periphery of the main ashcloud and (b) in the anbient air (dashed line)
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ambient air were 63 and 5 ug m respectively. Hydrogen sulfide concentrations
in the pl ume were high (about 0.5 ppm) but SO., concentrations were near ambient
val ues.
Exactly one week after the first explosive eruption of May 18, a second
violent eruption occurred. This eruption, which began at 0132 PST on Sunday May
25, sent an ash-rich cloud to 45,000 ft. by 0145 PST. Despite poor visibil ity
and rain showers (some ash-laden) our airborne measurements began in the erup-
tion cloud by 1000 PST. Particle size measurements in the ash pl ume (Fig. 6)
were simil ar to those obtained on May 18. However, unl ike May 18, we detected
fairly high levels of total sulfur gases in most of the ash clouds: 6-110 ppb
(compared to 6-14 ppb in the ambient air) with 13-95 ppb of hydrogen sul fide and
3-6 ppb of inert sul fur species.
Measurements on May 30 and June 4 showed the gaseous emissions to be con-
tinuing while the amount of ash decl ined. A significant fraction of the smaller
particles now appeared to be condensed sol uble material with quantities of
SO, Br", F~ and Cl’.
ACKNOWLEDGMENTS: Thanks are due to al members of the Cl oud and Aerosol Research
Group who hel ped (well beyond the normal cal l of duty) in obtaining these
measurements.
Without prompt administrative action on funding by Drs. B. Fogl e, E. Bierly,
R. Di rks and D. Senich of the National Science Foundation and Dr. w. Wil son of
the Environmental Protection Agency, the measurements reported herei n would not
have been obtained.
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10 10 10 10 10 01
PARTICLE DI AMETER D (^.m)
Particle size distributions at 11,400 ft altitude and 5
nautical miles downwind of Mt. St. Helens at 1029 PST on
May 25, 1980: (a) in the ash cloud (solid line) and (b)
in the ambient air (dashed line)