Question

Why was the Indian Ocean tsunami so disastrous?

Answer 1

The Indian Ocean tsunami of 2004 was so disastrous in terms of
loss of life and property because . . .

-- It was caused by an Earthquake of a type and at a depth that
cause exceptionally large tsunamis.

-- It hit parts of Indonesia, India, and Africa where low-lying terrain
extends far inland.  That made it possible for the sudden increase
in sea-level to push the wall of water far inland.

-- It hit parts of Indonesia, India, and Africa where the coastal areas
are densely populated.

-- It hit parts of Indonesia, India, and Africa where there is little or no
communication among densely populated coastal areas.  There were
hundreds of thousands of people who took no action to protect themselves
or their homes, because even several days after the Earthquake, nobody
in their villages knew what was coming.