Erta Ale volcano erupted on 16 Jan. 2017 in a difficult-to-access terrain in the Erta Ale volcanic range in Ethiopia. Like many other rifting ridge volcanoes, little is known about the properties of the deep magma plumbing system. Here, we analyze interferometric synthetic aperture radar data from different satellites between late Jan. 2017 and May 2019 to study the ground deformation after the start of the intrusion to infer the possible geometry and volume change of the magma reservoir that fed the eruption. We identified volcano-wide subsidence of up to 9 cm and horizontal contraction of up to ~5 cm that extend from Erta Ale to neighboring volcanoes. The modeling results suggest that an off-rift NE-SW elongated mid-crustal source is required to explain the observed volcano-wide deformation, but the depth is poorly constrained and the shape is complex. We suggest the presence of vertical interactions between stacked mid-crustal magma sources. Our study demonstrates that a considerable volume of melt could have been stored in mid-crustal magma reservoirs within the slow-spreading Erta Ale ridge to facilitate recent volcanic activity.