  Persistently active lava lakes show continuous outgassing and open convection
over years to decades. Ray Lake, the lava lake at Mount Erebus, Ross Island,
Antarctica, maintains long-term, near steady-state behavior in temperature,
heat flux, gas flux, lake level, and composition. This activity is superposed
by periodic small pulses of gas and hot magma every 5-18 minutes and disrupted
by sporadic Strombolian eruptions. The periodic pulses have been attributed to
a variety of potential processes including unstable bidirectional flow in the
conduit feeding the lake. In contrast to hypotheses invoking a conduit source
for the observed periodicity, we test the hypothesis that the behavior could be
the result of dynamics within the lake itself, independent of periodic influx
from the conduit. We perform numerical simulations of convection in Ray Lake
driven by both constant and periodic inflow of gas-rich magma from the conduit
to identify whether the two cases have different observational signatures at
the surface. Our simulations show dripping diapirs or pulsing plumes leading to
observable surface behavior with periodicities in the range of 5-20 minutes. We
conclude that a convective speed faster than the inflow speed can result in
periodic behavior without requiring periodicity in conduit dynamics. This
finding suggests that the surface behavior of lava lakes might be less
indicative of volcanic conduit processes in persistently outgassing volcanoes
than previously thought, and that dynamics within the lava lake itself may
modify or overprint patterns emerging from the conduit.
