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What does this talk have to do with MARGINS (I ask myself)? Ash results from Explosive VolcanismAsh results from Explosive Volcanism Explosions start from Gas escaping magma--CPB magmas carry as much as 10X more gas than other magmas!Explosions start from Gas escaping magma--CPB magmas carry as much as 10X more gas than other magmas! Gas escape from CPB explosive eruptions is up to two orders of magnitude more that erupted magma volumes would suggestGas escape from CPB explosive eruptions is up to two orders of magnitude more that erupted magma volumes would suggest Pyroclastic flows, which create most of the fine ash, are much more common in CPB eruptionsPyroclastic flows, which create most of the fine ash, are much more common in CPB eruptions Kilauea Puu Oo

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MARGINS, San Jos, Costa Rica June 22, 2007 William I Rose Michigan Tech Univ Houghton, MI 49931 USA The formation, fate and hazards of fine volcanic ash

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Acknowledgments Ash collectors of distal ash samples are few and far between. Here are several vital sources: Sam BonisAndrei Sarna-Wocjicki Sam Bonis for Guatemalan tephra. Andrei Sarna-Wocjicki for Mount St Helens. Game McGimseyNick Varley Game McGimsey for Cook Inlet volcanoes. Nick Varley for Colima. Joop VarekampJim Luhr Joop Varekamp and Jim Luhr for El Chichn. 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 : Raymond Shaw, 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 Cambridge University, Univ South Florida, USGS, Michigan Tech Institutional Help: Cambridge University, Univ South Florida, USGS, Michigan Tech US National Science Foundation Finances: US National Science Foundation

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Fine ash (

distal/fine New Laser diffraction data on distal/fine ashfall samples from 10 - >1000 km distance, mainly collected as they fell: VolcanoMagmaStyleVEIDates Fuego Basalt subplinian 2- 41973-74 San Miguel Basalt strombolian?11970 SpurrAndesitesubplinian 3-41992 ColimaAndesitepeleean/1-3?2000-2006 RedoubtAndesitepeleean2-31989-90 AugustineAndesitepeleean2-41986 PinatuboAndesite plinian61991 El ChichnTrachyandesite plinian 51982 St HelensDaciteplinian51980 SantiaguitoDacitepeleean1-21968-2006 Bruneau-JRhyoliteplinian811 ma

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Volcanic Clouds- the home of fine ash and a domain of both volcanology and meteorology Rapid fallout of coarse particles (30min) Clouds and precipitation Volcanic Clouds and ashfall Hydrometeors important in both clouds and VC CCN abundant in VC, rare in clouds Cloud glaciation early (-18 C) VC have many small icy particles that form during cloud ascent and sublimate. Clouds, especially vertically developed ones, develop larger hydrometeors. VC can become quite heavy with a load of fine particles--sinks as a whole

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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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Large pyroclasts Large pyroclasts (>0.5 mm diameter or < 1 ) fall out in stage 1 (

18 May 1980 fall deposits of MSH are very fine-grained (>50% 300 km. This suggests fallout of all particles together AJ Durant et al., 2007, in prep.

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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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Colima Volcano has produced ashfalls from both vertical explosions and from co-PF events during 2005-2007. We have compared 20 examples of each with results that show clearly-- although the bulk compositions are similar, the GSDs are systematically different, with the Co-PF samples being poorly sorted and with high content of fine grained particles. Evans, Varley, Huntoon & Rose, 2007 Co-PF Vertical Explosion

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Manam 27 Jan 2005 0355 UTC MODIS 1-4-3 True Ash-rich and ash-poor volcanic clouds--- Separation observed in many remote sensing examples

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Fuego has had >60 brief subplinian VEI 2-3 eruptions which produce mainly thin fall units that are unpreserved in the geologic record. 14 Oct 1974

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Bimodal GSD with two subequal modes.

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Normal ashfall, with dominant coarse mode Because this fine-grained mode is minor and was grouped in the pan portion of sieved samples, it is underappreciated and is quite common.

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General pattern of decreasing Md reflects changes only in the coarse mode

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Fine mode is located to WNW, while the bulk of the coarse ash is W to WSW HYSPLIT shows that 4 km winds are to WNW while winds at 8-12 km are W and WSW

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Above Ephrata on 18 May Photo by Douglas Miller Fully glaciated volcanic cloud with abundant CCN Density of cloud increases as a wholeDensity of cloud increases as a whole Latent heat effects significant in rise and possibly in fallLatent heat effects significant in rise and possibly in fall Bright band effects during descent (thawing)Bright band effects during descent (thawing) Overall sublimation/evaporationOverall sublimation/evaporation Quite different from a thunderstormQuite different from a thunderstorm

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Mammatus Simulation Kanak and Straka, Atmos. Sci. Let. 7: 28 (2006) ~6000 m Simulation time: 20 minutes! 10 m snow aggregate diameter contours dry sub-cloud layer snowflake aggregation induced entire layer descends thunderstorm cirrus outflow anvil

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Conceptual Model: Distal Fallout

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Meteorological Cloud Volcanic Cloud Many IN Small ice HM Little Precip Sublimation Few IN Bergeron Large Ice HM Precipitation

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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, 2005-2006 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. El Chichn 1982 Rose and Durant, in prep

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Conclusions Fine ash is especially generated in PFs; PF-rich eruptions have much more fine ash and this fine ash falls out prematurely in hours to a day.Fine ash is especially generated in PFs; PF-rich eruptions have much more fine ash and this fine ash falls out prematurely in hours to a day. Hydrometeors are a big part of the story of fine ashfall.Hydrometeors are a big part of the story of fine ashfall. Volcanic Clouds generate IN overseeding which inhibits precipitation.Volcanic Clouds generate IN overseeding which inhibits precipitation. GSD does not change with distances >~100-300 km-- fallout of whole cloud mass.GSD does not change with distances >~100-300 km-- fallout of whole cloud mass. Separation of volcanic clouds into higher, fine ash poor, gas rich and lower, fine ash rich portions which may disperse in different wind fields.Separation of volcanic clouds into higher, fine ash poor, gas rich and lower, fine ash rich portions which may disperse in different wind fields. Modeling of fallout cannot be derived from proximal fallout patternsModeling of fallout cannot be derived from proximal fallout patterns