Hoover Dam - 1986

Ah, das habe ich nicht gewusst.

200m hört sich wirklich sicher an. Kaum fassbare Mengen an Beton, die da transportiert werden mussten.

Yes, the dam held. In fact, it's still there today. But in a sense that compounded the disastrous effect: the water "jumped" over the dam and came down the valley with even greater and more concentrated violence. However, those responsible for the tragedy were not the dam designers or builders, but those who ignored the warnings of geologists first and the signs of an imminent landslide later. I was only 4 years old at the time but the shock and grief I sensed from the adults were so strong that those are the earliest memories I have. Well, those and snatches of olfactory memories of my grandma cooking ... :))

Actually, the dam was at risk when the reservoir was first filling, because the "grout curtain", injected into the bedrock below the dam before construction and intended to forestall leakage, turned out to be seriously inadequate. There was a _lot_ more leakage around the dam than had been expected, and the rock under the dam was swelling due to all the water it was absorbing. That was putting pressure beneath the dam and could have led to structural failure. There was a huge effort beginning in the late 30s and lasting into the late 40s to extend the grout curtain. It was very difficult because drilling into the bedrock below from _inside_ the dam, from the inspection galleries, was in extremely cramped conditions. The effort succeeded--the leakage dwindled and the swelling subsided--but it apparently was much more touch-and-go than reports at the time indicated. Furthermore, the failure of St. Francis Dam in southern California in the late 20s--still AFAIK the most catastrophic in the US--was fresh in everyones' minds. This whole retrofit is _not_ mentioned in most popular accounts of the construction! I found out about it from Hiltzik's _American Colossus: Hoover Dam and the Making of the American Century (2010).