Characterization of Bubbles and Their Formation during the Eruption of Damavand Volcano Scoria

Scoria is one of the main pyroclastic units in Damavand volcano, which its main crystals are plagioclase, olivine and pyroxene. In this study, characterization of bubbles and their formation during the eruption considered using Bubble Size Distribution (BSD) method including study of volume, 3D modeling, nucleation and bubble growth. For ed sample, thebubbles investigated in 3 perpendicular dimensions (X-Y-Z) and in total 16830 bubbles (X=7357, Y=5385, Z=4088) were measured and drawn. The Bubbles volumes calculated in 3 dimensions are X=47.21, Y=40.27, Z=40.01 percent. The Bubbles axes were calculated: X=1:1:4, Y=Z=1:1:3.4 and the 3D schematic shape is ellipsoid which the longest axis (L) is about 4 times longer than the other two axes (I, S). The L axis is parallel to the lowest pressure dictated on magma and the bubbles could be grown 4 times more in that direction. The bubbles shape of Damavand scoria is an ellipsoid with an average of 1:1:3.7 for its axes. The presence of 3 peaks in frequency distribution versus bubble size diagram, suggesting polymodal events of bubbles generation and in the Damavand volcano the bubbles nucleation occurred in 3 events(F1, F2, and F3). The nucleation density increased F1 to F3 but the bubbles growth reduced in the same direction. The first group of bubbles formed in the magma chamber and the second group formed during the magma ascent. The third group of bubbles could form either in the space between earlier groups or in the last stage of magma eruption.