In the Wallarah seam there are many places where layers of Tuff are above and or below the coal.

 

Using the bord and pillar mining method, pillars of coal were left to hold up the roof of the mine.

 

The volcanic ash (Tuff) is very fine and when wet, holds a large amount of water.  This causes it to expand and break apart the coal pillars that were left to hold up the roof.

 

The earliest instances of this occurred in 1874. On

separate occasions, falls of “top coal” killed two men in the New Wallsend mine.

 

Between 1874 and 1988 37 men were killed in

mining accidents at CHB (ELMHS records).

 

A partial solution to minimize roof falls was to leave part of the coal on both the roof and the floor.