Long Term Ground Deformation of Mount Raung as Inferred by InSAR and GPS Data

The eruptions of Mount Raung, located in East Java, Indonesia was characterized as explosive and effusive. The majority of eruptions that occurred before 1956 produced ash high into the air, and since 1921 the majority of eruptions have been lava flows to the base of the caldera. The most recent eruption occurred on January 21, 2021 where the ash column was observed to reach 400 - 1000 meters above the peak; on February 8 - 12 it even reached an altitude of 2000 - 2500 meters. Monitoring of lava (hotspot) has been carried out since February 6, 2021, which proceeded to cover almost to the entire caldera base. This eruption is probably a series of lava eruptions for the period November 2014 - August 2015 and July-August 2020. Currently, the main volcanic activity of Raung is located at the base of the elliptical caldera, measuring 1750 x 2250 m at a depth of 400-550 m below the embankment. The deformation activity of Mount Raung was observed by combining interferometric method and GNSS observation. Around 268 unwrapped interferograms since 2015 until January 2021 were provided by LiCSAR and processed by LiCSBAS method. The deformations are clearly shown on crater with deflation trend, whereas inflation trend is detected on the caldera. In short period, i.e. June to January 2021, inflation and deflation are detected on the crater. For terrestrial method, GNSS data from 3 stations that observed since December 2018 using the Leica SR30 receiver and processed by GIPSYX software. The data showed indication of deflation in the body of Mount Raung from December 2018 to mid-January 2021. Moreover, between mid-January to late February 2021 there was an indication of inflation in the peak areas. The analysis using shorter period should be able to observe the dynamics changes in the deformation of Mount Raung, but the long-term ones can determine the pressure accumulation process at the depth and the possibility of future eruption.