"disaster," 1848, from French débâcle "downfall, collapse, disaster" (17c.), a figurative use, literally "breaking up (of ice on a river) in consequence of a rise in the water," extended to the violent flood that follows when the river ice melts in spring; from débâcler "to free," from Middle French desbacler "to unbar," from des- "off" (see dis-) + bacler "to bar," from Vulgar Latin *bacculare, from Latin baculum "stick" (see bacillus).
The literal sense is attested in English from 1802, in geology, to explain the landscapes left by the ice ages. Figurative sense of "disaster" was present in French before English borrowed the word.