Mine engineers decided to encase just the top part of the shaft with steel tubing to prevent rockfalls and further collapses during the extraction process.
Scientists believe magma is now at a very shallow level and hot cracks in the dome are opening which is causing rockfalls on to the south crater floor.
The Vale of Glamorgan council says it regularly inspects this coastline but it admits it cannot predict the livelihood of rockfalls as that is something that occurs naturally.
After the incident at the San Jose mine, the Chilean government tightened mine security measures across the country, but injuries and deaths due to tunnel collapses and rockfalls remain a common problem.