I suspect many index funds were still holding GPM from its days...

I suspect many index funds were still holding GPM from its days as MFS Diversified. Perhaps reluctant to realise losses.

But with GPM's removal (effective from today) from the S&P All Ord index, they had no choice but to sell.

Thus the large volumes for most of last week. The buy side knocked right back under the pressure. No doubt this has also dislodged other holders concerned at the drop. Has provided others with an unexpected buying opportunity. I'd expect to see volume reduce now, so lets see it it happens.