Strange Tree Roots

Walking in the Royal Botanical Gardens in Hamilton ON, I came across this tree, with very strange-looking roots, shaped like big pots, tunnels, and barrels. The bank was eroded away on this side; on the other side the tree looked perfectly normal. I didn’t collect leaves to make an identification, so I don’t know what type of tree it is, and don’t yet know why the roots look so strange like this. Learning must continue! :-) Hopefully I’ll find the answer at some point.