A similar larger hole appeared near Blackheath about 9 years ago.
Caused severe traffic disruption for 3-4 years while it was was being filled in and investigated.
Apparently caused by 18th century chalk extraction mines collapsing.
You sure it is not caused by climate change?.
The heat on the tar soaks up the moisture which in turn leads to the increased expansion and contraction that causes it to fall in.
This theory may lead to the pits.
Surprised the friends of the earth have not jumped on this