India, Aug. 28 -- A disaster can unfold in a Himalayan valley in minutes. Understanding what actually happened can take much longer.

That is where satellites are beginning to change the picture.

Following the devastating flash flood that struck Nepal's Rasuwa district on August 26, India's National Remote Sensing Centre (NRSC), part of ISRO, began comparing satellite images captured before and after the event. The images show dramatic changes in the high-altitude terrain and along the Bhote Koshi-Trishuli river system, helping scientists reconstruct a disaster that began far above many of the communities it eventually affected.

The assessment remains preliminary. But it is already showing how Earth-observation satellites, seismic recor...