The Fukushima nuclear disaster was primarily caused by which event?

The Fukushima nuclear disaster was primarily caused by a combination of two significant natural events: an earthquake followed by a tsunami. On March 11, 2011, a massive earthquake struck off the coast of Japan, triggering a tsunami that ultimately inundated the Fukushima Daiichi Nuclear Power Plant. The tsunami caused critical failures in the plant's cooling systems, leading to reactor meltdowns and the release of radioactive materials.

While the tsunami itself had devastating effects, it was the earthquake that initiated the sequence of events leading to the disaster. Thus, the most accurate answer would highlight both elements, as the earthquake preceded and set off the tsunami, thereby causing the nuclear disaster. Therefore, focusing solely on the tsunami does not capture the full context of the events that contributed to the incident.