I'm no expert, but I understand that tsunamis do not appear threatening while over deeper water. Indeed, to someone out on the ocean, it appears as little more than a swell. When it hits shallower areas, however, it rises in height and becomes destructive. From the pictures, this stretch of beach appears to be fairly shallow for quite a ways.
"tsunamis do not appear threatening while over deeper water"
If you think about it, most waves are simply surface events caused by wind. The tsunami wave is a internal wave that goes from bottom to surface. It then becomes external as it compresses at the shore.