“The corbels at the top of the grand gallery have been found to ba hanging on by a fraction of an inch on one end, suggesting the structure was exposed to major stress such as an earthquake of unusual strength. OTOH, it may have happened during the event that cracked the granite blocks used to roof the King’s Chamber and the relieving chambers above it.”
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OTOH, it may have happened during the event postulated by C. Dunn - an explosion when some of the ingredients used in generating some sort of power didn’t mix correctly or some such. That idea accounts for the scorch marks in the Kings Chamber and the shifted granite blocks.
Only if imagination can move millions of tons of rock.