 Other factors contributed to the tsunami being largely undetected until it was too late, and although a tsunami watch was posted by an American tsunami warning center and a Japanese meteorological center, no information was delivered to people at the coast.The island of Java is the most densely populated island on Earth, and is vulnerable to both large earthquakes and volcanic eruptions, due to its location near the Sunda Trench, a convergent plate boundary where the Australian tectonic plate is subducting beneath Indonesia.Three great earthquakes occurred in the span of three years to the northwest on the Sumatra portion of the trench.