The December 26, 2004, disastrous tsunami event in the Indian Ocean may have come as a shock and even a surprise to the communities outside geosciences. However, tsunami events are a natural part of the geosystems in regions of submarine earthquakes, and they will continue to hit the region even in the future. Here we present evidence of former tsunami events both on Sri Lanka and on the Maldives. Submarine “sandstorms” driven by tsunami waves brought littoral deposits down into caves 21 to 38 m below sea level. Radiocarbon dates allow the comparison with related tsunami signals in fens and lagoons, and historical documentation. The terrible December 26 event has raised a general awareness of tsunami events. It has also generated the installation of necessary warning systems. We are in urgent need, however, of a long-term tsunami chronology for a realistic tsunami hazards assessment.