## 5 Discussion
### Post-Sliding Frank Deformation  
Interferometric signals due to degassing or magma withdrawal are typically a broader, more symmetrical fringe pattern, indicative of a relatively deep source (_i.e._, the depth of the magma reservoir, e.g., [12]). This is not what we observe after the eruption; instead, the fringe patterns suggest that the source causing deformation is rather surficial (Figure 3c). Thus, we can discount degassing and/or magma withdrawal as the causes of the subsidence measured on the southwest flank. A lack of inflation prior to the eruption additionally suggests that either magma was transported directly from depth (_i.e._, [14; 29]) or that it was already present in the shallow crust prior to the eruption. The latter has been suggested by several authors. [PERSON] [16] originally proposed that the petrographic and chemical uniformity of Pacaya's lavas through time implied a continuous supply of magma to an \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**i.d. (see Figure 6)**} & **Cumulative Days Post** & \multirow{2}{*}{**Maximum Deformation (cm/day)**} \\  & **Emplacement \({}^{\star}\)** & \\ \hline a & 49 & N/A \\ b & 78 & N/A \\ c & 124 & \(-\)0.11 \\ d & 216 & \(-\)0.06 \\ e & 262 & \(-\)0.02 \\ f & 308 & \(-\)0.02 \\ g & 1015 & \(-\)0.02 \\ h & 1413 & \(-\)0.006 \\ \hline \hline \end{tabular}  
* end of time interval spanned by each interferogram; \({}^{\ddagger}\) start of emplacement: 28 May 2010.  
\end{table} 
Table 2: Maximum deformation rate (in cm/day) of the 2010 lava flow shows that the rate of subsidence, and thus rate of cooling, decreases over time. Loss of coherence due to emplacement does not allow measurements to be made until 78 days after the initiation of the flow. Figure 6: Deformation rate of cross section A-A\({}^{\prime}\) in Figure 5d shows that lava flow subsidence is greatest in the center, which can be inferred to be the thickest part of the flow. open conduit. This has been further proven by excessive degassing at the volcano [30; 31; 32; 33; 34], which implies that Pacaya has a substantial convecting and circulating magma body near the surface that is degassing but not erupting completely on the surface [21; 33]. Additionally, gravity changes measured by [PERSON] [35] were accounted for by density changes caused by very shallow magma bodies (depths of 100 to 200 m below the surface). The measured subsidence is confined to the southwest flank and covers the same extent of material involved in the co-eruptive sliding event. During the May 2010 eruptions, the majority of tephra was distributed to the north due to prevailing winds, as evidenced by coherence of the lower flanks of the edifice in the interferogram that spans the eruption (Figure 3b). This confirms that erupted material did not reach some areas of post-eruption subsidence, making it unlikely that measured subsidence on the southwest flank is due to thermal contraction of hot erupted material alone (_i.e._, [36]). This subsidence continues for several months, however it decreases in rate and becomes confined to the upper flanks of the cone (Figure 3d,e). Therefore, it is likely due to mechanical clast repacking in response to co-eruptive displacement as material stabilizes and consolidates, with higher levels of repacking corresponding to areas of greater levels of prior slope displacement. However, we cannot discount some component of thermoelastic contraction on the upper flanks due to cooling of erupted material. Pre- and post-eruptive interferograms reveal that flank instability is confined to the May eruptions [22]. This is unique from other measurements of volcanic flank movement, which have typically been attributed to relatively slow (10 cm or less) and steady (up to tens of years) gravitational creep (_i.e._, [37] and references therein). Instead, movement seems to both initiate and cease rapidly, followed by dominantly vertical subsidence as the slope stabilizes.