Presentation on theme: "Eruzioni vulcaniche Lezione del 29 Marzo 2012. Eruzioni sottomarine."— Presentation transcript:
Eruzioni vulcaniche Lezione del 29 Marzo 2012
Frammenti di ceneri idrovulcaniche e pliniane
In this summary of hydrovolc anic experiments, four basic i nteraction phenomena, consi sting of melt fountaining, unsteady blasts, steady production of steam a nd ejecta, and the nonexplosi ve quenching of melt into globular shapes (blo bs), 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 of water:magma mass ratio. Ranges are indicated for Strombolian, Surtseyan (hydrovolcanic), and submarine 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
Volcanic Explosivity Index (VEI)
Morfologie monogeniche Coni di scorie saldate (Spatter cone) Coni di scorie stromboliane (Cinder cone) Coni di tufo, anelli di tufo Duomi lavici e spine Plateau monogenici Crateri Maar Caldere monogeniche
Coni di scorie saldate – Spatter cone
Cono di scorie saldate – Spatter cone
Cono di scorie stromboliane – Cinder cone
Coni di scorie stromboliane
Tuff cone, Main Ethiopian Rift
Characteristics of Tuff Rings, Tuff Cones, and Cinder Cones a CharacterTuff RingsTuff ConesCinder Cones Height-Width Ratio1:10 to 1:301:9 to 1:11 LithologyMostly 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 BeddingWell-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 SourceWater from aquifer or shallow lake Water from deep aquifer, deep lake, or marine environment Little or no water (magmatic) Mechanism of Ejecta Dispersal Pyroclastic surge, fallout, and slumping Pyroclastic surge and flow, fallout, and lahars Ballistic fallout and avalanching a From Heiken (1971).