Estimation of Magma Supply Volume at Merapi Volcano during 2022-2024

Merapi Volcano, situated at the boundary between Central Java Province and the Special Region of Yogyakarta, is regarded as one of the most active volcanoes in the world. Its high volcanic activity indicates the episodic movement and accumulation of magma within the volcano's shallow system. Surface deformation associated with such activity is monitored using the Electronic Distance Measurement (EDM) method, which records changes of slope distance (CSD) between benchmarks on flanks and summit reflectors. This study analyzes 17 EDM baselines from June 1, 2022, to December 31, 2024, to determine the influence of block movement and pressure source inflation on surface deformation. Block movement correction was applied to the northwestern sector, particularly for the 1888 lava dome block, which experienced a northwestward shift of approximately 4.24 meters, including 2.49 meters of vertical uplift. A grid search method was used to estimate the displacement vector and to model a spherical pressure source beneath the summit. The pressure increased fluctuated 0.9 and 35 MPa, with a cumulative increase of approximately 211 MPa. The total magma supply volume during the observation period was calculated at 9.31 ± 0.39 × 106 m3, with a fluctuating supply rate between 0.8 and 115 × 103 m3/day. The relationship between CSD, block movement, with a lesser but significant contribution from pressure-induced inflation. These findings provide insights into Merapi's shallow magmatic dynamics and may support future volcanic hazard assessments.