This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The eruption of the Anak Krakatau volcano in early September 2026 had effects far beyond the rumbling ground and ash that blanketed nearby areas. Hundreds of kilometers above Earth, satellite imagery from Sentinel-2 let us watch how the surface of the Anak Krakatau archipelago changed after the blast.
The most dramatic transformation occurred on Sertung Island, just west of Anak Krakatau. On Aug. 8, 2026, much of the island appeared green and densely vegetated. When the Sentinel-2 satellite passed over the area again on Sept. 8, most of that green signature had disappeared.
Part of the island instead appeared gray to brown—as if the island had lost its life in barely a month. But satellite images do not simply tell us whether plants are alive or dead. They record how Earth's surface reflects different wavelengths of light.
The abrupt change on Sertung therefore raises a series of questions. For soil scientists, those questions include: Are the plants dead or merely buried under ash? How much debris actually landed?
And what happens to this fresh volcanic material next? Remote sensing lets scientists examine vegetation, moisture, soil, rock and volcanic deposits in ways that are not obvious from ordinary photographs. One of the most widely used measures is the Normalized Difference Vegetation Index, or NDVI.
By measuring how green leaves reflect red and near-infrared light, it reveals both the presence and health of plant life on the ground. Before the eruption, vegetated parts of Sertung had an average NDVI of about 0.72, representing a strong vegetation signal. By Sept. 8, that signal had fallen to around zero.
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