Early reports blamed a volcanic eruption, but that turned out to be a translation error from Indonesian-language sources. The true cause was a landslide - a catastrophic gravitational collapse along a cape on the island's southern shore. A seismic observatory in Kupang, several hundred kilometers to the southwest, had recorded an earthquake of unknown magnitude at 12:42 a.m., just eighteen minutes before the tsunami struck. Whether the earthquake triggered the slide or merely accompanied it remains debated, but the scale of the collapse was staggering: an estimated fifty million cubic meters of rock and earth detached from the volcano's eastern portion. Roughly one-third of the Iliwerung edifice fell into the sea. The landslide crown sits at an elevation near the village of Atakore on Bauraja Hill, an ancient volcanic crater especially vulnerable to failure after heavy rains. The scar is still visible in satellite imagery decades later.

The tsunami swept into Labala and Waiteba Bays with devastating force, pushing inland and burying coastal settlements under thick layers of sand. In some areas, deposits reached considerable depth. The waves struck when resistance was impossible - at one in the morning, families were sleeping in homes built close to shore. In one section of the island alone, rescue workers discovered sixty bodies. The destruction was total in the worst-hit villages: homes razed, primary schools collapsed, market stalls reduced to debris. What made the disaster particularly cruel was its silence. There was no eruption column, no visible warning in the night sky - just the ground giving way and the sea rising in response.

The initial death count stood at 155 when the Indonesian military assessed the situation on July 23. Within days, the confirmed toll rose to 539, though only 175 bodies had been recovered. An additional 700 people were reported missing and presumed dead. Many victims were never found - swept out to sea or buried under debris too deep to excavate. The grim arithmetic of disaster meant that mass graves became necessary for the remains that were recovered. One haunting detail surfaced a week later: a human body was found inside a shark caught off Rote Island, far to the south. A medical examiner quoted by the newspaper Suara Karya determined the person had been dead for two days before the shark swallowed the remains, suggesting the body had drifted for days in open water before that encounter.

In the aftermath, fear proved almost as disruptive as the wave itself. Thousands of panicked inhabitants from nine coastal villages abandoned their homes and fled inland to Lewoleba, the main town in Lembata's central highlands. Local authorities tried to stop the mass evacuation - the influx strained Lewoleba's housing and resources - but the effort was futile. People who had watched their neighbors' homes disappear in the night were not going to stay near the water. The exodus reshaped the island's settlement patterns, concentrating population away from the vulnerable southern coast. Bauraja Hill and the slopes of Iliwerung remain geologically unstable, a landscape where heavy rains can reactivate old slide surfaces. The 1979 disaster was not the first time this volcano shed its flanks, and geologists do not expect it to be the last.