Morphology - nsm.buffalo.edu
4
Ash Flow Tuffs Ash Flow Tuffs References: Smith, RL, 1960, As flows. Geol. Soc. America Bull., 71:795-842. Sparks, RSJ, 1976, Grain size variations in ignimbrites and implications for the transport of pyroclastic flows: Sedimentology, 23:147-188. Encyclopedia of Volcanoes, pp. 581-599 Fluidization Fluidization • Upward gas velocity supports particles • A large range of sizes supported • Very large sorting coefficient • Gas escape structures • Pumice concentration zones • Elutriation • Low viscosity Morphology Morphology • Controlled by topography • Fill depressions • Even upper surface • Valley ponded deposits • Veneer deposits • Multiple lobes and fans • Lateral levees Pyroclastic Flows of 472 AD, Vesuvius AD 79 AD 472 contact Standard Section (Sparks, 1976) Standard Section (Sparks, 1976) • Layer 1 (ground layer or surge) • Layer 2 (flow unit) • Layer 2a (fine-grained basal) • Layer 2b (main body of flow) • Layer 3 (ash cloud)
Transcript of Morphology - nsm.buffalo.edu
Ash Flow TuffsAsh Flow Tuffs
References:Smith, RL, 1960, As flows. Geol. Soc.
America Bull., 71:795-842.Sparks, RSJ, 1976, Grain size variations in
ignimbrites and implications for the transport of pyroclastic flows: Sedimentology, 23:147-188.
Encyclopedia of Volcanoes, pp. 581-599
FluidizationFluidization• Upward gas velocity supports particles• A large range of sizes supported• Very large sorting coefficient• Gas escape structures• Pumice concentration zones• Elutriation• Low viscosity
MorphologyMorphology
• Controlled by topography• Fill depressions• Even upper surface• Valley ponded deposits• Veneer deposits• Multiple lobes and fans• Lateral levees
Pyroclastic Flows of 472 AD, Vesuvius
AD 79
AD 472
contact
Standard Section (Sparks, 1976)Standard Section (Sparks, 1976)
• Layer 1 (ground layer or surge)
• Layer 2 (flow unit)
• Layer 2a (fine-grained basal)
• Layer 2b (main body of flow)
• Layer 3 (ash cloud)
Base of Bandelier TuffBase of Bandelier Tuff
soil
fall
2a
2b
Gas PipeGas Pipe Honeycomb Hills, UtahHoneycomb Hills, Utah
Plinian fall
2a
2b
Komagatake Tuff, JapanKomagatake Tuff, Japan
Pyroclastic fall
Pyroclastic flow
Soil
fall
AshAsh--flow Sheets, Smith (1960)flow Sheets, Smith (1960)
• Flow units
• Cooling units
• Welded tuffs
• Compound cooling units
Welding (Ragan & Sheridan)Welding (Ragan & Sheridan)
• Degree of welding– Non-welded
– Partially welded
– Densely welded
• Density is a good index
• Welding (density) profiles
Partly Welded Bishop Tuff
Partly Welded Bishop TuffPartly Welded Bishop Tuff
Pumice
Vitrophyre, ArmeniaVitrophyre, Armenia
Secondary CrystallizationSecondary Crystallization
• Vitrophyre
• Devitrification
• Lithophysae
• Vapor-phase crystallization
• Zeolitization
Sheet MorphologySheet Morphology
• Generally plateau forming
• Steep marginal escarpments
• Non-welded upper layers removed
• Erosion of soft material into teepees
Teepees, Bandelier TuffTeepees, Bandelier Tuff
