The scientists studied how the Aceh River delta in Sumatra, Indonesia has changed over time. They used different methods like imaging, logging, and surveys to map the landforms and sediment deposits in the area. The map they created shows rivers, beaches, tidal flats, and more. By looking at buried sediment layers, they found evidence of where the river used to flow. They also discovered that the delta has grown towards the sea by about 7-8 kilometers since the sea level was higher thousands of years ago.