The correct answer is Tectonic movement. Explanation & Key Takeaways: • Tsunamis are among Earth’s most infrequent hazards and most of them are small and nondestructive. • Over deep water, the tsunami has very long wavelengths (often hundreds of kilometres long) when a tsunami enters shallow water, its wavelength gets reduced and the period remains unchanged, which increases the wave height. • Tsunamis have a small amplitude (wave height) offshore. This can range from a few centimetres to over 30 m in height. However, most tsunamis have less than 3 m wave height. • It radiates in all directions from the point of origin and covers the entire ocean. • It generally consists of a series of waves, with periods ranging from minutes to hours.