## 3 Results
### Subsidence in Lava Fields outside the EFA  
The cumulative vertical displacement during the 2009-2014 period and the lava thickness for each selected lava flow emplaced outside the EFA are shown in Figure 4. All lava flow fields outside the EFA show a trend of downward movement with varying degrees of magnitudes. From a visual inspection, large subsidence occurs generally in and adjacent to thick areas (Figure 4). To quantitatively characterize the relationship between the subsidence and the thickness of the lava flow fields, we divided coherent pixels into several small bins according to thickness (1 m unit). Displacements in each bin are statistically analyzed and plotted in function with thickness in Figure 5, on the background of the population distribution histogram. The Mar 1998a lava thickness ranges from one meter to fifteen meters, giving a slight cumulative subsidence of \(\sim\)0.03 to \(\sim\)0.06 m during the \(\sim\)5.5 years period. The Mar 1998b lava field (up to 30 m thick) subsides cumulatively \(\sim\)0.02 to \(\sim\)0.12 m. The Feb 2000 lava (up to 20 m thick) subsides \(\sim\)0.02 to \(\sim\)0.1 m in total. The Apr 2007 lava field (thickness up to 25 m) shows an overall downward displacement of \(\sim\)0.02 to \(\sim\)0.25 m. Figure 5 shows that the subsidence magnitude increases with the raising of flow thickness (a positive correlation) following clear linear laws in all cases. We fitted the correlation using linear functions and the best fits are presented in red lines with norm of residuals, marked alongside, indicating good linear fits (Figure 5). The low values of norms of residuals (\(\sim\)0.01 m, \(\sim\)0.07 m, \(\sim\)0.03 m, and \(\sim\)0.12 m for the Mar 1998a, Mar 1998b, Feb 2000, and Apr 2007 lava fields, respectively) confirm the linear relationship between subsidence and thickness in the selected lava fields outside the EFA, though one order of magnitude larger norm of residuals was obtained from the Apr 2007 lava field. The absolute subsidence-thickness (m/m) slopes of four lava flow fields (0.0014, 0.0013, 0.0016 and 0.0028 for the Mar 1998a, Mar 1998b, Feb 2000 and Apr 2007 lava fields, respectively) show that the magnitude of subsidence occurring in one meter thick lava increases with the decrease of lava age. The younger Apr 2007 lava subsides \(\sim\)0.0028 m per meter (thickness) during the 2009-2014 period (Figure 5d), which is about twice larger than the magnitude of subsidence occurring in the 10 years older lava flow fields (the Mar 1988a-b lava fields; Figure 5a,b). The Mar 1998a lava field (Figure 5a) exhibits an absolute subsidence-thickness slope of 0.0014, approximate to that of the Mar 1998b lava field that emplaced in the same year (0.0013; Figure 5b) and a bit smaller than that of the Feb 2000 lava field that emplaced two years later (0.0016; Figure 5c). To investigate the temporal behavior of subsidence, we selected one point of 10 m thickness in each lava field outside the EFA (see Figure 4 for location of points) as representatives and plot the displacement time series in Figure 6a. The four time series display a similar trend, revealing the four lava fields subside following a similar temporal behavior between 2009 and 2014--continuous subsidence without being clearly interrupted by volcano eruptive phases and a subsidence rate decaying with time. For the lava field that emplaced in Feb 2000 (green triangles in Figure 6a), the magnitude of subsidence rate (at the 10 m thick point) decays from \(\sim\)0.04 m/year at the beginning of study period (nine years after it emplaced) to \(\sim\)0.01 m/year about five years later, a reduction of three quarters. Figure 4: Cumulative U-D displacement and thickness maps for four lava fields located outside the Eastern Flank Area (EFA). (**a**) Mar 1998a lava field, (**b**) Mar 1998b lava field, (**c**) Feb 2000 lava field, and (**d**) Apr 2007 lava field.