The 2004 tsunami took about two hours to reach Sri Lanka after the earthquake. The country was far enough from northern Sumatra that the waves crossed the Indian Ocean before striking its shores, unlike parts of Aceh that were hit within minutes.
The earthquake occurred off the west coast of northern Sumatra on 26 December 2004. Sudden movement along the Sunda megathrust displaced the seafloor and pushed a vast volume of seawater outward. Tsunami waves then travelled rapidly through deep ocean, slowing and changing shape as they approached shallower coastal waters.
Sri Lanka’s eastern coastline was the first part of the island to be struck because it faced the source region. Waves later travelled around the southern tip at Dondra Head and inundated the southwestern coast as well. This means “two hours” is an approximate island-wide answer, not an identical arrival time for every beach.
Travel-time estimates are often confused with the tsunami’s arrival in India, Thailand, or Indonesia. Nearby shores in northern Sumatra were reached much sooner, while Sri Lanka and parts of India were generally hit roughly 90 minutes to two hours after the earthquake.