The scale of Japan’s catastrophe is hard to believe. Never mind the nuclear meltdown that is still unfolding — that’s its own category of bad news. But the earthquake and tsunami have essentially given Japan the equivalent of 10 Katrinas. Ten times as many people perished, at least. Sendai, a city of more than a million people, was swamped. Ishinomaki, population 162,000, was demolished. And several smaller cities, parked in narrow bays that amplified the waves, have effectively disappeared. Minamisanriku is gone. Rikuzentakata is gone. Onagawa is gone.

You’ve seen the videos so I don’t need to explain how bad this was. But it’s still hard to grasp the destructive force applied by the sea to these coastal communities.

All kinds of numbers have been flying around about the height of the tsunami that hit northern Japan. You hear 10 meters, generally, but also 23 meters, the latter of which puts the wave well past 70 feet and is rather improbable. What makes this hard to pin down is that there’s not a single wave, but rather a train of waves. The whole ocean tips onto land, essentially. Local geography can amplify the height of the water. Some reports may be describing the “runup” of the water as it impacts a building or some other structure or obstacle. A scientist tells me this morning:

“The highest inundation depth (as opposed to wave heght and runup) in an open coastal area is 12.8 m at the beach opposite Sendai airport. All other reports higher than that appear to be either runup, or in one case at Onagawa, are amplified by the shape of the Bay (to 14.8 m).”

We know Japan can, and will, rebuild. But even a technological advanced country is going to need help and support from the rest of the world. Consider the basic question: Do you rebuild the cities in the same location, knowing that it could happen again? If you don’t, how do you compensate people for the loss of their land and homes? How do you rebuild not only the infrastructure but the way of life?

This is going to take many years.