Digital mapping of soil organic carbon in volcanic soils after prolonged eruption Mt. Sinabung, Karo Regency, North Sumatra, Indonesia

Abstract Mount Sinabung (at Karo Regency, North Sumatra) has been considered as an active volcano since 2010, and after three years of inactivity, the volcano’s activity resumed in 2013. The deposition of volcanic ash buried everything on the soil surface with various thicknesses. Volcanic ash is a valuable inorganic material and consists mostly of primary minerals. But with time, these materials can initiate carbon storage through the revegetation process. This study investigates carbon storage and sequestration in volcanic soils affected by the intermittent eruptions of Mt. Sinabung. A total of 34 soil samples were collected from areas of 3 to 7 km from the eruptive vent. The samples were analyzed to determine labile-C, very labile-C, total-C, Organic-C, non-crystalline-C, and metal complex-C fractions. Regression kriging (RK) was applied to spatially predict the carbon distribution. The results showed that the highest labile-C was 1.65% found in the Southeast slope and the lowest, 1.20%, in the Southern slope. The highest value of very labile-C was in the Southeast (1.20%), and the lowest was in the Northern (0.46%). The highest (11.66%) and lowest values (8.84%) of total C were in the Northeast and South slopes, respectively. The highest Organic-C value was detected 7.42% in the Northeast volcanic soils, and the lowest, 5.74%, is in the South slopes soil. The lowest non-crystalline- C was found in the soils of Northeast slope (0.60%), and the highest was in the Southeast (0.82%) soil. While the highest metal complex-C value was 0.88% in the Southeast, and the lowest is 0.36% in the soil of South slope. These data show that the highest carbon storage is parallel with the direction of the ash distribution, which tends to the Southeast side of Mt. Sinabung. The results of this study demonstrated that volcanic regions have a strong resilience capacity to bounce back after devastating natural hazards. Volcanic deposits interact with atmospheric water to initiate vegetation regrowth and create a carbon pool within their particles.