Publication Date:
2017-04-03
Description:
Volcanic eruptions are characterized by intense degassing, thus it is imperative to have high quality laboratory data to constrain degassing
mechanisms. In order to investigate bubble formation and growth at 1 atm, degassing experiments using a Stromboli basalt were performed on the
GSECARS X-ray beamline at the Advanced Photon Source. Volatile-bearing glasses were synthesized at 1250 °C and 1000 MPa in a piston
cylinder with H2O or mixtures of H2O+CO2; they were then heated in-situ on the X-ray beamline at 1 atm. Bubble growth was observed in-situ
using X-ray radiography. The 3D bubble size distributions in the quenched samples and a natural Stromboli pumice were studied by synchrotron
X-ray microtomography.
The results show that bubble nucleation and growth in basaltic melts are volatile-concentration dependent. Bubbles can easily form in melts
initially containing high volatile concentrations. The effect of CO2 on bubble nucleation and growth becomes significant at large CO2
concentrations of 880 to 1480 ppm, but is not important at lower concentrations. Multiple nucleation events occur in most of these degassing
experiments, and they are more pronounced in more supersaturated melts. Bubble growth is controlled by viscosity near glass transition
temperatures and by diffusion at higher temperatures. Bubbles begin to pop 10 to 20 s after a foam is developed at vesicularities of 65% to 83%.
Bubble size distributions follow power–law relations at vesicularities of 1% to 65%, and bubble size distributions evolve from power–law
relations to exponential relations at vesicularities of 65% to 83%. This evolution is associated with the change from far-from-equilibrium
degassing to near-equilibrium degassing. During far-from-equilibrium degassing, multiple nucleation events are pronounced, and possibly account
for the generation of power–law relations. When the system reaches near-equilibrium degassing, coalescence is dominant and leads to the
formation of bubbles of similar size. Therefore, bubble size distributions are described by exponential relations.
Description:
NSERC
Description:
Published
Description:
533-547
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
JCR Journal
Description:
reserved
Keywords:
basalt
;
Stromboli
;
bubble size distribution
;
degassing
;
04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
