Axisymmetric gravity currents that result when a dense suspension inru
des under a lighter ambient fluid are studied theoretically and experi
mentally. The dynamics of and deposition from currents flowing over a
rigid horizontal surface are determined for the release of either a fi
xed volume or a constant flux of a suspension. The dynamics of the cur
rent are assumed to be dominated by inertial and buoyancy forces, whil
e viscous forces are assumed to be negligible. The fluid motion is mod
elled by the single-layer axisymmetric shallow-water equations, which
neglect the effects of the overlying fluid. An advective transport equ
ation models the distribution of particles in the current, and this di
stribution determines the local buoyancy force in the shallow-water eq
uations. The transport equation is derived on the assumption that the
particles are vertically well-mixed by the turbulence in the current,
are advected by the mean flow and settle out through a viscous sublaye
r at the bottom of the current. No adjustable parameters are needed to
specify the theoretical model. The coupled equations of the model are
solved numerically, and it is predicted that after an early stage bot
h constant-volume and constant-flux, particle-drived gravity currents
develop an internal bore which separates a supercritical particle-free
region upstream from a subcritical, particle-rich region downstream n
ear the head of the current. For the fixed-volume release, an earlier
bore is also predicted to occur very shortly after the initial collaps
e of the current. This bore transports suspended particles away from t
he origin, which results in a maximum in the predicted deposition away
from the centre. To test the model several laboratory experiments wer
e performed to determine both the radius of an axisymmetric particle-d
riven gravity current as a function of time and its deposition pattern
for a variety of initial particle concentrations, particle sizes, vol
umes and flow rates. For the release of a fixed volume and of a consta
nt flux of suspension, the comparisons between the experimental result
s and the theroetical predictions are faily good. However, for the cur
rent of fixed volume, we did not observe the bore predicted to occur s
hortly after the collapse of the current or the resulting maximum in d
eposition downstream of the origin. This is unlike the previous study
of Bonnecaze et al. (1993) on two-dimensional currents, in which a str
ong bore was observed during the slumping phase. The radial extent R o
f the deposit from a fixed-volume current is accurately predicted by t
he model, and for currents whose particles settle sufficiently slowly,
we fine that R= 1.9(g'V-0(3)/v(s)(2))(1/8), where V is the volume of
the current, v(s) is the settling velocity of a particle in the suspen
sion and g'(0) is the initial reduced gravity of the suspension.