Constraints on cooling and degassing of pumice during Plinian volcanic eruptions based on model calculations

Abstract

Abstract. During explosive volcanic eruptions, pumice clasts are transported into the atmosphere, and their thermal and degassing histories determine how much volatiles are lost syneruptively. This process is studied by combining a steady state eruption column model with a model for the cooling and degassing of pumice. In the model we investigate the impact of various parameters (e.g., mass eruption rate, Blot number, eruption temperature, and geometry) on the cooling and degassing of If this ratio is larger than 50, degassing of the pumice will be nearly complete with a few percent of the original volatiles left in the outer rind of the pumice. For a ratio of less than 0.1 no volatiles escape the pumice. Typical values for thermal and species diffusivity as well as vesicle wall thickness indicate that in the case of degassing C1 and HeO the transition from 0.1 to 50 will be in the pumice size range of 1-10 cm. Here volatile concentration is a strong function of position inside the pumice, suggesting that values for volatile contents measured on picked matrix glass from crushed samples may not be the best way to estimate the volatile content of matrix glass, a number which is frequently used to estimate the total volatile input of volcanic eruptions. This effect is even more pronounced when looking at hydrogen isotopic fractionation with larger pumices tending toward 5D • -120%o and small samples giving 5D > -800/00 .

Determining volcanic eruption styles on Earth and Mars from crystallinity measurements

“…The overall decrease in clast size in Martian explosive volcanism particularly affects groundmass crystallization in aircooled pyroclasts since cooling times are proportional, and cooling rates are inversely proportional, to the particle radius 27 . Assuming a spherical cooling model, particles oB1 cm rapidly re-equilibrate with their surroundings and remain in thermal equilibrium with the erupted gas in which they are entrained 1,27 .…”

“…Assuming a spherical cooling model, particles oB1 cm rapidly re-equilibrate with their surroundings and remain in thermal equilibrium with the erupted gas in which they are entrained 1,27 . The cooling rate of small (o1 cm) erupted particles therefore is controlled by the cooling rate of the eruption plume they are in equilibrium with.…”

“…The cooling rate of small (o1 cm) erupted particles therefore is controlled by the cooling rate of the eruption plume they are in equilibrium with. Numerical simulations of a near-vent gas thrust model transitioning to a convective plume 27,28 modified for Martian atmospheric pressure and temperature 29 , eruption velocities and vent diameters 1 , and magma composition 30 (Supplementary Table 1) are coupled with cooling ratecrystallization rate relationships above an estimated glass transition temperature of B730°C (refs. 18,31) to reconstruct syn-eruptive groundmass crystallization during plinian eruptions on Mars (see Supplementary Discussion 1 for details of numerical modelling).…”

Ash iron mobilization through physicochemical processing in volcanic eruption plumes: a numerical modeling approach

“…As a first order approximation, the travel time from the vent to the NBL is 150-250 s during which the plume temperature is lowered by ∼ 800-1000 • C (Hort and Gardner, 2000). Thus, the mixture cooling rate is in the range of 4-7 • C s −1 in the convective region of the plume.…”

“…Solubility of iron in airborne particles (e.g., mineral dust) is known to be strongly linked to its chemical speciation and mineralogy (Schroth et al, 2009;Journet et al, 2008). However, it is not yet fully un- Ayris et al (2013), Hort and Gardner (2000) and Rose and Durant (2009) for conduit, plume and cloud zones, respectively; b high-T: T > 600 • C, mid-T: 150 • C < T < 600 • C and low-T: 50 • C < T < 150 • C; c warm zone: T > freezing point (∼ 0 • C), cold zone: T < freezing point.…”