Publication Date:
2017-04-04
Description:
We investigate the effect of crystal size on the rheology of basaltic magmas by means of a rheometer
and suspensions of silicon oil with natural magmatic crystals of variable size (from 63 to 0.5 mm) and
volume fraction fi (from 0.03 to 0.6). At constant fi, finer suspensions display higher viscosities than
coarser ones. Shear thinning (flow index n 〈 1) occurs at fi 〉 0.1–0.2 and is more pronounced (stronger
departure from the Newtonian behavior) in finer suspensions. Maximum packing and average crystal size
displays a nonlinear, positive correlation, while yield stress develops at fi 〉 0.2–0.3 irrespective of the
crystal size. We incorporate our results into physical models for flow of lava and show that, with respect
to lava flows containing coarser crystals, those with smaller crystals are expected to: 1) flow at lower
velocity, 2) have a lower velocity gradient, and 3) be more prone to develop a region of plug flow. Our
experimental results explain the observation that phenocryst-bearing and microlite-bearing lavas at Etna
volcano (Italy) show smooth pahoehoe and rough aa’ surfaces, respectively.
Description:
FIRB-MIUR ‘‘Research and Development of
New Technologies for Protection and Defense of Territory
from Natural Risks’’
Description:
Published
Description:
2661-2669
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
JCR Journal
Description:
restricted
Keywords:
rheology
;
magmatic suspensions
;
analogue model
;
lava flo
;
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
