Sturkell et al. (2013) studied Hekla’s last eruption in 2000 using campaign GPS; an InSAR interferogram; dry tilt data, and borehole strain data. They found the presence of a dike that “causes surface fissuring extends no more than ~ 0.5 km in depth, and the reservoir depth is ~ 10 km. These are connected by a conduit of small lateral extent. Data for previous eruptions are consistent with this model”.
There are numerous studies based on deformation datasets published on Hekla and yield estimated reservoir depths from 5 to 10 km (Sturkell et al. 2013 and references therein). In general “Hekla shows a few long-term precursors to eruptions: optical tilt, GPS and InSAR give indications of upcoming eruptions” (Sturkell et al. 2013).