Eruzioni vulcaniche
Lezione del 29 Marzo 2012
Eruzioni sottomarine
Frammentidi ceneri
idrovulcaniche
epliniane
In this summary of hydrovolcanic experiments, four basic interaction phenomena, consisting of melt fountaining, unsteady blasts, steady production of steam and ejecta, and the nonexplosive quenching ofmelt into globular shapes (blobs), are correlated to volcanic activities and the water:melt mass ratio (Rm ).
Scaled kinetic energy relative to the initial melt thermal energy is shown as a function ofwater:magma mass ratio. Ranges are indicated for Strombolian, Surtseyan (hydrovolcanic), andsubmarine activity as well as for corresponding landform and deposit bedforms.(Adapted from Wohletz and McQueen, 1984.)
D = area compresa nell’isopaca 1/100 di quella massima
F = % piroclastiti < 1 mm all’intersezione tra asse di dispersione e isopaca 1/10 della massima
VEI Description Plume Height Volume Classification How often Example
0 non-explosive <100 m 1000s m3 Hawaiian daily Kilauea
1 gentle 100-1000 m 10,000s m3 Haw/Strombolian daily Stromboli
2 explosive 1-5 km 1,000,000s m3 Strom/Vulcanian weekly Galeras, 1992
3 severe 3-15 km 10,000,000s m3 Vulcanian yearly Ruiz, 1985
4 cataclysmic 10-25 km 100,000,000s m3 Vulc/Plinian 10's of years Galunggung, 1982
5 paroxysmal >25 km 1 km3 Plinian 100's of years St. Helens, 1981
6 colossal >25 km 10s km3 Plin/Ultra-Plinian 100's of years Krakatau, 1883
7 super-colossal >25 km 100s km3 Ultra-Plinian 1000's of years Tambora, 1815
8 mega-colossal >25 km 1,000s km3 Ultra-Plinian 10,000's of years Yellowstone, 2 Ma
Volcanic Explosivity Index (VEI)Volcanic Explosivity Index (VEI)
Morfologie vulcaniche
Poligeniche Monogeniche
Positive Negative
Morfologie monogeniche
Coni di scorie saldate (Spatter cone)Coni di scorie stromboliane (Cinder cone)Coni di tufo, anelli di tufoDuomi lavici e spinePlateau monogeniciCrateriMaarCaldere monogeniche
Coni di scorie saldate – Spatter cone
Cono di scorie saldate – Spatter cone
Cono di scorie stromboliane – Cinder cone
Cono di scorie stromboliane – Cinder cone
Coni di scorie stromboliane
Tuff cone, Main Ethiopian Rift
Characteristics of Tuff Rings, Tuff Cones, and Cinder Conesa
Character Tuff Rings Tuff Cones Cinder Cones
Height-Width Ratio 1:10 to 1:30 1:9 to 1:11 1:9 to 1:11
Lithology Mostly sideromelane tuff and lapilli-tuff, with substantial amounts of palagonitic tuff breccia containing blocks of lava and sediments; some accretionary lapilli
Palagonitic and sideromelane tuff and tuff breccia, possibly scoria and lava within the vent, abundant accretionary lapilli
Tachylitic cinders and scoria, traces of sideromelane ash, lava flows
Bedding Well-defined, relatively thin beds, massive bedding where base was below local water level
Poorly defined, relative thick beds, some thin beds at the base and top
Massive bedding, poorly defined
Sedimentary Structures
Well-developed graded bedding with dune, massive, and plane-parallel structures, impact sags around ballistic fragments, soft sediment deformations
Graded bedding at base and top, bulk of cone is nongraded massive beds, soft-sediment deformations
Crude inverse grading in avalanche structures
Water Source Water from aquifer or shallow lake
Water from deep aquifer, deep lake, or marine environment
Little or no water (magmatic)
Mechanism ofEjecta Dispersal
Pyroclastic surge, fallout, and slumping
Pyroclastic surge and flow, fallout, and lahars
Ballistic fallout and avalanching
a From Heiken (1971).
Plateau lavico monogenico A
B
C
• Duomi lavici
EndogeniEsogeni
Duomo lavico, Mount St. Helens
St. Helens
Mount St. Helens
Plug dome e Spina
Lipari,
Duomo esogeno, Castello d’Ischia
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