Recent satellite images of Fentale volcano in Ethiopia have revealed a mysterious white feature or “blob” within the crater, prompting much speculation about its origin. While some have suggested it may be a rising volcanic plume – or even SO2, I believe the white area is actually a growing body of steaming, white cloudy water – and is likely a consequence of groundwater intrusion into fractures formed by deflationary processes.
Satellite images taken a day apart from Landsat 8 RT (Jan 16) and Sentinel 2 L2A (Jan 17) show a very similar shape for the white feature, which is not the expected behavior for a dynamic plume.
If we also compare the reflectance values in the near-infrared (NIR) and green bands, we can see an NDWI index of ~0.6-0.7 – strong evidence for a water body. The output image shows a near circular (possible) water body obscured by rising steam. The Normalized Difference Moisture Index (NDMI) shows very high moisture content in this area, as well as an area to the south-east. More recent satellite imagery from yesterday shows the white “blob” expanding to the south-east also, further suggesting that more water is rising from the ground.
Although no thermal anomalies have been detected within the crater, wispy clouds in the satellite images suggest the water body may be hot and releasing steam. If it is water, the likely cause is the result of increased permeability of the rock due to deflation and fracturing. This allows groundwater to penetrate deeper, where it is heated and then rises back to the surface. There may have been a preceding or ongoing hydrothermal eruption.
Ongoing monitoring of sulfur dioxide (SO2) emissions has not detected any significant increases.
Sources: Sentinel 2, Landsat 8, TROPOMI, Landviewer, Planet Labs