Satellite Observations of the ongoing April 2015 Eruption of Volcán Calbuco, Chile

Ebmeier, González, Bagnardi, Carboni, Hayer, Pyle & Mather

On the 22nd April Calbuco volcano, Chile, erupted for the first time since 1972, with very little warning. Plumes of volcanic ash reached heights of 16 km on the 22nd and up to 17 km in a second, longer duration eruption that began in the early hours of 23rd April.   Over about 7.5 hours Calbuco is thought to have erupted around 0.2 km3 of ash.

Several thousand people were evacuated from villages closest to Calbuco .   Ash fell over an area extending from the west coast of Chile to the east coast of Argentina, and grounded air traffic in Chile, Uruguay and Argentina. The area worst affected by ash fall extends north and east from Calbuco, where ash thicknesses were around 50 cm, towards Bariloche, where about 1 mm of ash has been reported. Intermittent, low-level ash plumes continue to rise from the vent, and there is a continuing hazard associated with secondary lahars around the volcano.

There appears to have been only a very brief period of precursory activity before the eruption. A swarm of volcanic tremor earthquakes began at 15.11 and continued until the start of the eruption at 18.05 local time (SERNAGEOMIN). No deformation was measured in Sentinel interferograms from the month before the eruption up until the 21st April.

Figure 1. Sulphur dioxide retrieval (Dobson units) for the 27th April 2015 [Carboni].
Figure 1. Sulphur dioxide retrieval [Dobson units] for 27th April 2015
Large volumes of SO2 were released during the eruption of the 22nd-23rd April, with emissions continuing at a lower level up until at least the 27th April (See IASI retrievals, Figure 1). First estimations are that the Calbuco eruption released 0.2 -0.4 million tonnes of SO2. This flux is much larger than the Chaitén eruption of 2008 (0.01 Mt SO2), but comparable to the SO2 release during the Cordon Caulle eruption in 2011 (0.25 Mt).

The difference in backscatter of Sentinel images acquired on the 14th and 26th April show that the topography of Calbuco’s crater changed during the eruption (Figure 2). In particular, some material seems to have been removed from the summit, potentially part of the ice cap, leaving a much deeper crater than was there previously.

Figure 2. Radar backscatter images of Calbuco volcano on the 14th and 26th April 2015. Differences between the two images are due to changes in the scattering and reflecting properties of the ground, caused by the deposition of explosive deposits and removal of material at the volcano’s crater [Ebmeier].
Figure 2. Radar backscatter images of Calbuco volcano on the 14th and 26th April 2015. Differences between the two images are due to changes in the scattering and reflecting properties of the ground, caused by the deposition of explosive deposits and removal of material at the volcano’s crater [Ebmeier].
 Although there is no evidence for deformation before the eruption, a Sentinel interferogram from the 14th – 26th April shows that a region centred to the southwest of Calbuco subsided during the eruption.   Deformation has a maximum magnitude of about 12 cm in satellite line of sight. A particularly interesting aspect of the signal is that it is centred not on the volcano’s edifice itself, but several kilometres away from it. Preliminary modelling suggest that this deformation pattern can be fitted by a Mogi source contracting by 49 +/- 8 x 106 m3 about 5.5 km southwest of the volcano at a depth of ~10 +/- 1 km (Figure 4).

All Sentinel-1 results are Derived Works of Copernicus data (2015), subject to the following use conditions: “TERMS AND CONDITIONS FOR THE USE AND DISTRIBUTION OF SENTINEL DATA“.

Figure 3. Maps of displacement at Calbuco
Figure 3. Map of displacements at Calbuco between the 14th and the 26th of April shown as centimetres range change in the satellite line of sight , so that blue represents movement away from the satellite. [González & Ebmeier].
Figure 4. Data, spherical source elastic half space model and residuals for recent deformation at Calbuco [Bagnardi].
Figure 4. Data, spherical source elastic half space model and residuals for recent deformation at Calbuco [Bagnardi].