Pliny the Younger

About 21 centuries ago today Vesuvius buried Pompeii in a manner as horrific as the wall of water did in northern Japan.  Obviously those closest to the disaster were not able to report it.  We know of accounts via letters from Pliny - here being one:

"Ashes were already falling, not as yet very thickly. I looked round: a dense black cloud was coming up behind us, spreading over the earth like a flood.'Let us leave the road while we can still see,'I said,'or we shall be knocked down and trampled underfoot in the dark by the crowd behind.'We had scarcely sat down to rest when darkness fell, not the dark of a moonless or cloudy night, but as if the lamp had been put out in a closed room. 
You could hear the shrieks of women, the wailing of infants, and the shouting of men; some were calling their parents, others their children or their wives, trying to recognize them by their voices. People bewailed their own fate or that of their relatives, and there were some who prayed for death in their terror of dying. Many besought the aid of the gods, but still more imagined there were no gods left, and that the universe was plunged into eternal darkness for evermore".
That's about it if you want to have an account.  One can imagine but only in the context that our eyes have seen volcanoes erupt and have enough movie references so we kinda "get it" as to the horror. Tidal waves in movies tend to be of the Poseidon Adventure scale with a 100 feet of water barrelling towards a ship or shore and, like a broom, everyone and thing is swept clean. Japan's tragedy seemed different - like some ooze, some spilled bucket of mud, that just came coming out of an endlessly deep bucket.  But in the end, there you fire or by water, by ash or by mud.