  Recent ALMA observations have revealed that a large fraction of
protoplanetary discs contain bright rings at (sub)millimeter wavelengths. Dust
trapping induced by pressure maxima in the gas disc is a popular explanation
for these rings. However, it is unclear whether such pressure bumps can survive
for evolutionary time-scales of the disc. In this work, we investigate an
alternative scenario, which involves only dust-gas interactions in a smooth gas
disc. We postulate that ALMA rings are a manifestation of a dense, clumpy
mid-plane that is actively forming planetesimals. The clumpy medium itself
hardly experiences radial drift, but clumps lose mass by disintegration and
vertical transport and planetesimal formation. Starting from a seed ring, we
numerically solve the transport equations to investigate the ring's survival.
In general, rings move outward, due to diffusion of the clump component.
Without pressure support, rings leak material at rates $\sim$40
$M_\oplus\,\mathrm{Myr}^{-1}$ and in order for rings to survive, they must feed
from an external mass reservoir of pebbles. In the case where the pebble size
is constant in the disk, a cycle between ring formation and dispersion emerges.
Rings produce large quantities of planetesimals, which could be material for
planet formation and explain the massive budget inferred debris disc. Mock
images of ALMA observations compare well to the rings of Elias 24 and AS 209
from DSHARP's sample.
