Satellite images from the Sentinel-2 satellite have shown major changes to the Anak Krakatau archipelago after a volcanic eruption in early September 2026. The most noticeable transformation occurred on Sertung Island, located west of Anak Krakatau. On August 8, 2026, the island appeared green and heavily covered with vegetation. However, by September 8, much of that green color had vanished, with many areas turning gray or brown. Scientists are now trying to understand whether the plants are dead or just covered in ash, and how much volcanic debris actually landed on the island. To measure the health of the vegetation, scientists used the Normalized Difference Vegetation Index (NDVI), which analyzes how green leaves reflect red and near-infrared light. Before the eruption, Sertung Island had an average NDVI of about 0.72, indicating dense vegetation. By September 8, this number had dropped to near zero. However, a drop in NDVI doesn't always mean the plants are dead—factors like a fresh layer of ash, fallen leaves, physical damage, or even weather conditions can create similar readings. To get more detailed information, scientists also looked at other parts of the satellite spectrum, such as shortwave infrared (SWIR) wavelengths. These wavelengths help assess plant moisture and the physical composition of the surface. Before the eruption, Sertung showed signs of being a densely vegetated island. After the eruption, much of the surface reflected the characteristics of nonvegetated material. Another index, the Normalized Difference Moisture Index (NDMI), also showed a sharp decline in moisture signals from the vegetation, supporting the idea of significant environmental change. In contrast, Panjang Island, located just east of Anak Krakatau, retained a strong green signal even after being affected by the 2018 eruption. This is likely because the ash plume from the 2026 eruption drifted west and southwest, sparing Panjang from heavy ashfall. This difference between the two islands gives scientists a rare chance to study how wind patterns and ash distribution affect the survival of ecosystems. While satellite images can show where the surface has changed, they cannot determine the exact nature of the material involved. For that, scientists need to collect samples and analyze them in laboratories. Chemical analysis can reveal which elements are present and their concentrations, while mineralogical analysis can identify the types of minerals and volcanic glass in the newly deposited material. These properties will influence how the environment changes over time, as rainwater reacts with the minerals and glass, releasing chemical elements and altering the surface. Microorganisms may colonize the deposits, and plant residues may begin to break down, allowing pioneer plants to grow in areas where conditions are suitable. Anak Krakatau first emerged above sea level in 1930, long after the devastating 1883 eruption. Since then, scientists have observed cycles of volcanic activity, erosion, vegetation growth, and ecological recovery. Sertung Island is an interesting case because it was already well vegetated before the 2026 eruption. This means that fresh volcanic debris has landed on an established ecosystem, raising questions about whether the vegetation will quickly return once ash is washed away by rain, or if some areas might be buried too deeply for rapid recovery. Erosion could also redistribute the new material before plants can recolonize it. The next satellite image may provide some answers to these questions, but others may take years to resolve. Studying active volcanoes has become less reliant on dangerous fieldwork, as satellites can now show where environmental changes have occurred and how quickly the landscape responds. Field observations can determine what has survived, and laboratory analysis can reveal the composition of the new material. Soil science can explain how this material interacts with water, organisms, and time as the landscape continues to evolve.