  Measurement of volcanic CO2 flux by a drone swarm poses special challenges.
Drones must be able to follow gas concentration gradients while tolerating
frequent drone loss. We present the LoCUS algorithm as a solution to this
problem and prove its robustness. LoCUS relies on swarm coordination and
self-healing to solve the task. As a point of contrast we also implement the
MoBS algorithm, derived from previously published work, which allows drones to
solve the task independently. We compare the effectiveness of these algorithms
using drone simulations, and find that LoCUS provides a reliable and efficient
solution to the volcano survey problem. Further, the novel data-structures and
algorithms underpinning LoCUS have application in other areas of fault-tolerant
algorithm research.
