Premium
High‐speed imaging of Strombolian eruptions: Gas‐pyroclast dynamics in initial volcanic jets
Author(s) -
Taddeucci J.,
AlatorreIbarguengoitia M. A.,
Palladino D. M.,
Scarlato P.,
Camaldo C.
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl064874
Subject(s) - strombolian eruption , pyroclastic rock , geology , drag , jet (fluid) , mechanics , ejecta , volcano , physics , seismology , astrophysics , supernova
High‐speed imaging of Strombolian explosions brings into view the motion of pyroclasts upon leaving the volcanic vent. The erupted gas‐pyroclast mixtures form jets with well‐defined leading vortex rings that rise at almost constant velocity proportional to the time‐averaged velocity of pyroclasts. The ejection velocity of pyroclasts decreases over time and defines a conical profile centered on the jet central streamline. Pyroclast deceleration patterns are related to their velocity and compatible with drag force but are also strongly controlled by jet dynamics. These patterns include constant, decreasing, or abruptly increasing decelerations up to 10 4 m s −2 . Nonuniform deceleration focuses at the jet sides and, mostly, in a narrow zone across the vortex ring. This deceleration zone is trailed by a reduced drag zone, where deceleration is drastically reduced. In these highly transient eruptions, both zones move upward and attenuate over time. Our results provide the first quantitative mapping of reduced drag zones.