2004 Tsunami: 18 years of devastating event, people pay tearful homage to victims

Explaining The Universe on Instagram: "A tsunami doesn’t begin with towering waves crashing onto shore, it often starts deep beneath the ocean. Most tsunamis are triggered by powerful undersea earthquakes, when tectonic plates suddenly shift and displace massive amounts of water. This sudden movement creates a pulse of energy that travels outward across the sea. In the open ocean, tsunami waves may only be a few feet tall and pass unnoticed beneath ships, but they move incredibly fast, up to 500