Viewing a single comment thread. View all comments

maedchenhosen t1_j5ddftt wrote

Reply to comment by SierraVictoriaCharli in TIL that the California St. Francis Dam disaster of 1928, a midnight-hour 120' wave that killed 431 sleeping people and wiped out giant sections of land more than 50 miles west to Ventura, was caused by the dam having been built on a fault zone (in addition to the dam's retention of water). by atrailofdisasters

I thought it was schist, not gypsum. Can you point me to where it says gypsum was the issue?

4

SierraVictoriaCharli t1_j5f17g7 wrote

https://en.wikipedia.org/wiki/St._Francis_Dam The investigation section cites multiple contradictory investigations and the reasons for some of their bias (This all happened in the run up to the Hoover Dam and the feds were watching closely) but one of the later investigations points the finger at saturation and deformation in the east bank as a potential triggering fault. The fact both abutments failed while the center section stood is pretty phenomenal really, and suggests that neither abutment stood on a competent foundation; iirc the schist failed the western abutment (that and the talc), and the gypsum and clay deposits failed the eastern abutment.

5

maedchenhosen t1_j5f6mai wrote

Thank you!!! I’ve been to the site and climbed over to the western edge - the schist there is clearly weak. It’s hard to believe they thought it’s be ok :(

2