Experimental investigations of granular matter flow regimes leading to insight into lahar flow dynamics : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Manawatū, New Zealand
The flow of granular material governs numerous natural processes including the aeolian
dynamics of sand dune formation, sub-aerial and submarine mass flows, the collective
dynamics of ice blocks floating on the ocean, avalanches of debris and snow,
as well as volcanic granular-fluid flow processes, such as pyroclastic density currents,
volcanogenic debris flows and lahars.
Lahars are a particularly important type of granular flow, in regards to its possible effect
on human life; they are debris and water-based flows, initiated by volcanic processes.
A fascinating aspect about granular matter is the co-existence of behaviour similar to
two or all three of the classical states of matter (solid, liquid, gas) and their frequent
transitions between these behaviours. Despite the ubiquity of these transitions in nature
and industry, the fundamental physics of granular matter remains a mystery, to
the extent that a unified theory to describe the motion and behaviour of granular matter
is still absent.
This study is an attempt to simulate lahars and their erosion/deposition mechanics in
the laboratory by making use of a rotating drum. A rotating drum can be treated as an
analogue for a lahar because it allows for erosion and deposition to occur as an active
region of material flows over a passive, erodible bed. In nature these processes are
transitory and highly dynamic, but an experimental analogue allows for the processes
to be observed in a steady system.
Results include detailed maps of the various regions in a flowing granularmaterial correlated to the speed of rotation of the flows. The changing status of the active and
passive regions allows for measurements of the erosion mechanics within the drum.
Also, potentially identified are two new phenomena; high speed rotations appear to
include features similar to Kelvin-Helmholtz instabilities, and enclosed regions of subrotation,
which are referred to as self-enclosed circulation cells (SECCs).