Figure 3 Thickness change map from a) June 2–11 b) July 2–27 and c) September 9–17 showing observable emplacement processes. d) ΔV/Δt as a function of vent distance for each phase in five zones (see inset for location); G: Geldingadalir, M: Meradalir, SM: Syðri-Meradalur, N: Nátthagi and NE: the plateau northeast of the vent. The black line is the total ΔV/Δt for all five zones as a function of vent distance. In phase 1 all lava was deposited in Geldingadalir and thus the total ΔV/Δt is equal to the ΔV/Δt for Geldingadalir. The lower panel shows the total deposition from March to September between zones as a function of vent distance.
The lava deposition as a function of vent distance changed markedly over time. In phase 1 all lava was emplaced within Geldingadalir; and, in phase 2, as new vents opened on the northeast plateau, lava migrated into Meradalir and Syðri-Meradalur. In phase 3, the lava field expanded to its current maximum extent, reaching 3.3 km from the vent by having lava ponds acting as reservoirs for the transport system (Fig. 3d). This lava transport system closed during phase 4, when the continuous lava effusion was replaced by episodic activity responsible for large overflows and significant stacking in the vent region. Stacking and inflation was continued in Meradalir, where the lava reached a distance of 2.8 km from the vent. Thus, despite the long-term TADR in phases 3 and 4 was similar (Fig. 2), the difference between continuous and episodic activity at the vent had a major impact on the lava transport system and the ability of the lava field to expand. In phase 5, most lava emplacement was within a 1 km radius of the active vent but reached 2.7 km in mid-September after the drainage of a pond northwest of the crater (Fig. 3c). Between surveys this variation of lava deposition between zones amounted to as much as 10 m3/s for Geldingadalir and Meradalir, 5 m3/s for Syðri-Meradalur and the Northeast plateau and 3 m3/s for Nátthagi. Thus, despite a stable TADR, the local effusion into individual valleys varied significantly between surveys providing a great challenge for forecasting the timing of lava spilling from one valley to another.