VOLCANIC PROCESSES ESS 462
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This 21 page Class Notes was uploaded by Miss Jeanette Keebler on Wednesday September 9, 2015. The Class Notes belongs to ESS 462 at University of Washington taught by Staff in Fall. Since its upload, it has received 49 views. For similar materials see /class/192672/ess-462-university-of-washington in Earth And Space Sciences at University of Washington.
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Date Created: 09/09/15
Magma from a volcanologist s perspective Components and physical properties Components of magma Melt Silicate melt viscosity range Glass Quenched melt w no internal order Crystals ol cpx 0px lib cmmingtonite plag FeTi oxides 0 Gas Main gases in order of abundance H20 C02 802 H28 HCI HF Main gases in increasing order of solubility in silicate melt C02 H20 302 others Controls P T 02 Si02 of melt dissolved vs discrete bubble phase Tsolidus Rigid Crust Mush WWW wi 39 lt WWW w crystal free magma Schmincke 2004 Basaltic magma Kilauea Volcano Pele Dancing quot39 Karla Kra Daciti c magma Photo John Pallislery 3605 Why do these two lava ows look so different Why do these two lava ows look so different Answer Orders of magnitude differences in viscosity 102 vs 21010 Pas Cammm pattsms f strain in respmss m stmss Shear stress I V Yield strength Strain rate rate of ow 1 Control on melt viscosity Composition especially SiO2 Viscosity resistance to ow a Results from chemical bonding in melt Si cation and O anion are most abundant in magmas so largely control viscosity Si02 tetrahedraform bonds which produces chains these get tangled in ow and so produce resistance to shear stress Th 3 Main Controls on Mgh Vlgmsmy 14 Melt Composition 7 T RHYOLITE 2 12 6 20 1 8 4 5 s 10 emperature 5 100m Hgoltwt O Dlssolved water log VISCOSITY Pa 5 0 log VISCOSITY Pa 5 ANDESITE 4 THOLEHTIC BASALT 2 BASALT 0 l l I I I I I l I 500 1000 1500 TEMPERATURE C CRYSTALLINIT Y 31 vol 1 antml m1 Magma ViS SityZM61tViSC Sity 2 wm l Magma Vismsity Crystallir ty E M a H lmk gm mY J IgM J I I I I I I I I I I I 80 CRYSTALUNIW vs SiOz ATKAISLAND 70 0 DIKES x PLUGS 50 K 50 x IVE LAV gt5 3 r B N A gt g 40 NON o QO E 39 o o 30 o e de 0 J g 20 5 t 5 LAVAs xx g 0 M J 5 1 sao2 x o I J I I J 4 JI l I I I 46 50 54 58 62 66 70 96km sao Marsh 1931 JIIrfaLagILIQm I F L from Marsh 1981 What about microlites These too will increase viscosity substantially But most microlites don t form until shortly before the eruption when the magma is S few 100 m from surface 0 If they form earlier that magma probably won t make it to the surface Another control on magma Viscosity Bubbles starting with capillary number NCa 1393th of VISCOUS and surface tension stresses If small NCa bubbles resist stretching stay spherical If high NCa bubbles deform easily become elongate Ref Manga and Loewenberg 2001 Bubbles Tune I w j gt v v 1 k I h I preserved V0 I as vesicles come in many shapes Cashmcm el al 2000 HQW dQES Ca affEQt ViSCOSity 50 quot I quot39H quot 1 quotquot I 39 quot 1 quot39I quot 1 quot I quot 1 quot 50 If Max packing r spheres m0637 gt 0 U I I o I I O O I o I i I O 39S 10 an I o15 2 quotquot 39 quot quot39 E 39 n oso q 5 01 o quota L 2 o45 02 1 a m n 1 a 1 n a 02 10 5 105 Capillary number NCO from Pal JVGR 2002977 Relative viscosity 7 Hereas the some amoeth plotted as bubble VS relative VilSCQSiWa for high VS low NCa I 04 High Capillary Number 39 I 39 I Relative viscosity nr 02 A Exptal data 1 0 Numerical data 6 I Exptal data 15 3 00 I L L 000 015 030 045 050 Volume fraction of bubbles It from Pal JVGR 2003 8 39 I 39 I 39 I 39 I Low Capillary i 39 l l l 5 Cl Exptal data 53 I Exptal data 54 I o l I I I l n L n 00 01 02 03 04 05 06 07 Volume fraction of bubbles 4 Pal 2003 Now let s look more at volatiles and their exsolution from melt 105 l l l I l l I y W 1 aquot fjWe w Rhyolite 1050 C Increase in CO2 solubility with increasing P c Basalt 1200 C O Basalt 1400 C O Basanite 1400 C B Mgmelililite 1400 C A Olleucitile 1400 C l Sodamelilite 1400 C Albite 1450 C A Camelilitile 1500 C O U 5 E CO exsolution accelerates at 7 kbar 25 km l l l l l l g 0 510152025303540 Pressure kbars for MPa x 100 Blank and Brookequot 1994
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