We estimated the plume transport time, defined as the time between plume emission at Piton de la Fournaise and plume arrival at Maïdo, by using wind speed observations from Maïdo and Piton Partage (see section 2.2.2.2, see Figure ). We assumed that observations at Piton Partage were representative of conditions encountered by the plume after exiting the vent and the initial plume rise. Our estimate additionally assumes that 1) the plume travelled a distance of 38.5 km (the linear distance between Maïdo and the vent, see Figure ) and that 2) the average wind speed during plume transport was the average of the wind speed at "plume arrival" (at Maïdo) and the wind speed at "plume departure" (at Piton Partage). This is described in detail in Appendix B. As this estimate was obtained through several assumptions and simplifications, we assign to it a large relative uncertainty (k = 2) of 40%.