Dangerous rot

Immediate response from Islington tree officer to call from Tree Trust member meant this Highbury street tree was removed the same day. Pictures show extent of rot. Notice the almost vertical paving slab on the other side of the tree - was it on the move already? Are the holes part of the vascular system of the tree? Did insects play a part? How much of this rot was hastened by using the base of the tree as a dump for rubbish and rock salt heap in the winter?

Picture shows inside of tree decay cavity, taken upwards towards saw cut.