The moai are half buried because that's just what tends to happen in erosive environments. Sediment buries things. As for specifically debunking his LGM specul

The moai are half buried because that's just what tends to happen in erosive environments. Sediment buries things. As for specifically debunking his LGM speculation, there isn't much because no one with public credentials wants to spend time and effort on it in the current academic environment. You can find debunkings in popular media (https://www.youtube.com/watch?v=-iCIZQX9i1A https://www.youtube.com/watch?v=-iCIZQX9i1A) and a few scattered "popular" academic publications like the SAA's special edition on Hancock's pseudoarchaeology (http://onlinedigeditions.com/publication/?i=634462&p=10&view=issueViewer http://onlinedigeditions.com/publication/?i=634462&p=10&view...), but most of the information is buried in papers and books that don't discuss him at all. There's just flat out no actual evidence for (virtually?) all of his speculation and you can't prove a negative. Hancock's MO is to take 1-2 anomalous results and spin out media around "these dates don't line up, so let's speculate about something entirely unrelated". The rapa nui episodes in Ancient Apocalypse S2 talk to one actual archaeologist, who doesn't even support the dates discussed in the episodes. They were just anomalous banana phytoliths that were present from sediment intrusions. Dating is hard and this stuff happens regularly, especially in areas without much active research like Rapa Nui. The standard understanding is post-1200, as documented in papers like https://doi.org/10.1016/j.jas.2020.105094 https://doi.org/10.1016/j.jas.2020.105094 and https://doi.org/10.1038/s41586-021-03902-8 https://doi.org/10.1038/s41586-021-03902-8