Early Volcanic Clouds as seen from fallout, remote sensing and radar

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Early Volcanic Clouds as seen from fallout,
remote sensing and radar

• William I Rose, Adam J Durant
• Michigan Tech University

VAWS Workshop, Rotorua, March 2007
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Outline
Focus on El Chichón and Pinatubo Largest events
with relevant data--

• Remote Sensing constraints
• Mass/time/place of fallout
• Meteorology
• New data on fall deposits
• Grain size distributions
• Origin of fine particles
• Shape, distribution
• Interpretation of fallout

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Current retrieval algorithms for volcanic
clouds 1. volcanic ash masses and particle size
Wen Rose, 1994 JGR 99 5421-5431 atmospheric
corrections Yu et al, 2002, JGR 106 D16 2. 8.6 mm
SO2algorithm Realmuto et al, 1997, JGR 102
15057-15072. 3. 7.3 mm SO2algorithm Prata et al,
2003, GRL 4. TOMS UV SO2algorithm Krueger et al,
1995, JGR 100 14057-14076. 5. Multi-band IR
sulfate aerosol masses and sizes Yu Rose,
2000, AGU Monograph 116 87-100. 6. Multi-band IR
ice-ash-sulfate masses and sizes Guo et al, 2004,
G3.
We use all of these together for the study of
volcanic cloud evolution with time.
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• Ash went east and south
• SO2 went west
• Ash decreased very rapidly and fell out over N
  Chiapas and the Peten
• Lower level winds (12-20 km) dispersed the ash,
  while upper level winds ( 21-30 km) dispersed the
  SO2

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Band 4 Brightness Temperature, 2100 Z April 4,
1982
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Brightness Temperature Difference, 2100 Z April
4, 1982
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Missing ash
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Klyuchevskoi
El Chichón, Pinatubo
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Examples of Ice in Volcanic Clouds

• Ice Clearly Dominant
• Rabaul 1994
• Hekla 2000
• Ice Clearly Subordinate
• Spurr 1992
• Augustine 1986
• Cleveland, 2001
• Kluchevskoi, 1994
• Subequal ash and ice
• Montserrat (Boxing Day, 1997)
• Pinatubo (15 June 1991)
• El Chichón (4 April 1982)

250 KT fine ash No ice detected
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• hydrometeorAny product of condensation or
  deposition of atmospheric water vapor, whether
  formed in the free atmosphere or at the earth's
  surface also, any water particle blown by the
  wind from the earth's surface.
• liquid or solid water particles formed and
  remaining suspended in the air, for example, damp
  (high relative humidity) haze, cloud, fog, ice
  fog, and mist
• 2) liquid precipitation, for example, drizzle
  and rain
• freezing precipitation, for example, freezing
  drizzle and freezing rain
• solid (frozen) precipitation, for example, snow,
  hail, ice pellets, snow pellets (soft hail,
  graupel), snow grains, and ice crystals
• 5) falling particles that evaporate before
  reaching the ground, for example, virga
• 6) liquid or solid water particles lifted by
  the wind from the earth's surface, for example,
  drifting snow, blowing snow, and blowing spray.

From AMS glossary
Hydrometeors are probably more abundant than
volcanic particles in many or most young (lt12
hrs) volcanic clouds!
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• Ash and ice were together in EC cloud, as in
  Pinatubo
• The fine EC ash fell out in about 12 hours as the
  ice signal in remote sensing disappeared.
• This contrasts strongly with the SO2 cloud, which
  grew for days.
• Tropical Atmospheres are moist and convection
  associated with the PF/eruption cloud must cause
  a lot of entrainment of moist lower tropospheric
  air

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Grain size data in this paper comes from New
data on size distributions of more than 200
fine-grained volcanic ashfall samples from
basaltic, andesitic and dacitic
eruptions. Techniques used Laser Diffraction
automated particle grain size distributions using
equipment used in a variety of industrial
applications. The principle of this method is
forward fraunhofer scattering. The manufacturers
(instruments) are Malvern Instruments
(Mastersizer) and Microtrac (S3500). www.malvern.c
o.uk www.microtrac.com New Results Much
improved GSD data, especially for samples with a
high proportion of particles finer than sieve
ranges (lt63 µm diameters). These instruments
determine GSDs in the ranges of lt0.5 to 2000 µm
(-1 to 11 ?).
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New Laser diffraction data on distal/fine
ashfall samples from 10 - gt1000 km
distance Volcano Magma Style VEI
Dates Fuego Basalt subplinian, PF 2- 4
1973-74 San Miguel Basalt strombolian?
1 1970 Spurr Andesite subplinian 3-4
1992 Colima Andesite peleean/PF 1-3?
2000-2006 Redoubt Andesite peleean, PF 2-3
1989-90 Augustine Andesite peleean, PF 2-4
1986 Pinatubo Andesite plinian, PF 6
1991 El Chichón Trachyandesite plinian, PF
5 1982 St Helens Dacite plinian, PF 5
1980 Santiaguito Dacite peleean, PF 1-2
1968-2006 Bruneau-J Rhyolite plinian PF 8
11 ma
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VF 74-103 17 Oct 1974 Fuego. This distal fall
has only a very minor coarse mode, with a
dominant mode at 5 ?.
Sieve range
Laser diffraction expands the range of precise
GSD work to submicron diameters.
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Fall Deposits, B C












1 mm B C isopach
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CH-70 25 km NE Mean 166 µm ?? 1.4
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CH-8 35 km SW Mean 111 µm ?? 2.0
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CH-23 50 km SE Mean 252 µm ?? 1.4
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CH-19 80 km SE Mean 19 µm ?? 1.6
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CH-47 205 km E Mean 24 µm ?? 1.8
gt20 lt10 µm
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CH-74 195 km E Mean 23 µm ?? 1.8
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CH-82 140 km E Mean 29 µm ?? 1.9
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CH-49 180 km E Mean 24 µm ?? 1.8
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CH-1 85 km NNW Mean 22 µm ?? 1.8
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EC-1 280 km E Mean 11 µm ?? 1.5
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EC-1 280 km
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CH-1 85 km
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CH-19 80 km
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The aerodynamic size of a pyroclast strongly
influences its life in the atmosphere.
Large pyroclasts (gt0.5 mm diameter or lt 1 ?)
fall out in stage 1 (lt30 mins) and form
exponentially thinning ash blanket. Most of the
volume of pyroclasts is in this group and they
are found in thick fall deposits close to the
volcano. Medium size pyroclasts (0.5 mm to 50 µm
1-4 ?) fall out as simple particles in stage 2
(lt1 day) and bring smaller pyroclasts out with
them. Fine pyroclasts (lt50 µm gt 4 ? ) fall with
larger pyroclasts, may nucleate precipitation and
fall, especially during stage 1 and 2, and may
aggregate due to atmospheric turbulence and stick
due to static forces or moisture.
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Fall of spherical particles in earths atmosphere
Schneider et al., 1999, J Geophys Res 104
4037-4050
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El Chichón B C Isopach map in mm
Fines dominate
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20
10
5
1
DRE volume estimate 0.18 km3
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Overall the whole deposit is 85lt1 mm and 42 lt
65 µm Varekamp et al., 84, p 52
Figure 10 (from Varekamp et al. 85) Weight
fractions of fallout finer than 1 mm and 65
microns plotted against distance from the vent.
Note that samples beyond 50 km are made up
entirely of particles lt 1mm.
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Pinatubos July 15, 1991 eruption column was fed
by a co-ignimbrite cloud and the ashfall was
marked by a much more prominent fine ash
proportion. Such clouds likely entrain more
water vapor also. Dartevelle et al, 2002,
Geology 30 663-666.
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Carey Bursik, Encyc of Volcano-logy
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Origin of particles in volcanic clouds Explosive
vesiculation-- As pressure drops in ascending
magma--overpressured bubbles burst Hydrothermal
explosions--rock fractured by thermal shock from
contact between magma and water Milling--
abrasion and grinding of particles can occur in
pyroclastic flows and in the vent Chemical and
meteorological processes-- condensation,
sublimation, surface chemical reactions forming
acids, salts, hydrometeors and aggregates of
mixed origin
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GRL 32 L24808 2005
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Eruption style and the size of ash produced. The
total grain size distribution of an explosive
eruption can be estimated from the deposit, if
enough is known about all parts of the fall
deposit. Experiments suggest that energetic
eruptions produce more fine ash by vesiculation
alone. Several examples show clearly that
pyroclastic flows contribute large fine fractions
to the overall GSD, presumably by milling
(Soufrière Hills--Bonadonna et al, 2002
Pinatubo--Dartevelle et al., 2002 Fuego, 1974
Rose et al., 2006 AGU Fall Mtg El Chichon, 1982
Rose, 2007.)
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Why do fall deposit thickness/distance plots
sometimes show secondary maxima?
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Fallout of fine ash during stage 2 Aggregation
observed in laboratory and the field Accumulation
by collision/coalescence-- analogy with
meteorological clouds Areas of secondary maxima
marked by bimodal SD fallout of particles of
expected size occurs WITH much smaller
particles Highest masses of fine ash may occur on
dispersal axis or on the side Evidence for
fallout with ice noted Observations of mammatus
clouds Remote sensing shows that a vast majority
of fine ash falls out in stage 2
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El Chichón fall materials

• Contain high proportions of fine-grained
  particles, tend to be polymodal and are rather
  poorly sorted, like other co-ig deposits
• Fell out quickly and very close to source
• Descriptions of the samples are marked with
  statements about clustering and armouring

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Interpretations

• Fine ashfall from co-PF origin
• Fine ashfall mostly in a few hours
• Ice played big role in accelerated ashfall
• Ash blanket extends to Peten has gt20 of
  particles lt10 µm
• Ash dispersal by lower cloud than SO2
• -possibly because of Co-PF dispersion

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Individual eruption analyses underway/completed
Pinatubo fall deposits Dartevelle et al 2002
Geology 30 663-666. Bruneau-Jarbridge 11 my
rhyolitic fall deposit Rose et al 2003 J Geol
131 115-124. Fuego 14 Oct 1974 Rose et al, Bull
Volcanol in review. Fuego Feb-Mar 1973 eruptions
Rose et al, in prep. Mount St Helens, 18 May
1980 Durant et al., in prep. Colima, 2000-2006
co-PF and vertical explosion ashfalls J Evans
MS thesis MTU, in prep. Santiaguito 1968-2005
co-PF and vertical explosion ashfalls Rose et
al., in prep. Crater Peak/Spurr 1992 eruptions
Durant et al., in prep.
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Acknowledgments
Ash collectors of distal ash samples are few and
far between. Here are several vital sources Sam
Bonis for Guatemalan tephra. Andrei
Sarna-Wocjicki for Mount St Helens. Game
McGimsey for Cook Inlet volcanoes. Nick Varley
for Colima. Joop Varekamp and Jim Luhr for El
Chichón. Lab facilities access and enthusiastic
critical help Komar Kawatra, Costanza
Bonadonna, Clare Horwell, Alain Volentik Students
(who really did the work) Adam Durant, Colleen
Riley, Jason Evans, Sebastien Dartevelle Helpful
participants in data discussions Steve Self,
Gerald Ernst, Jackie Huntoon, Jocelyn
McPhie Miscellaneous vital help, mainly
technical Chris R Copeland, Owen Mills, Ken
Wohletz, Simon Blott, Steve Boreham and Chris
Rolfe Institutional Help Cambridge
University, Univ South Florida, USGS, Michigan
Tech Finances US National Science Foundation
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I have .pdf copies of 25 articles referred to in
this presentation, ready to copy onto your
laptop. These will also be added to the Workshop
website.