The partial or full tree defoliation, that followed the 1908 explosion, can prevent the formation of late wood and can give origin to a tree ring less dense, less colored and more friable than the other rings. Combining optical microscopy observation with the use of Computerized Axial Tomography (CAT),
the clear light rings can be easily found and their age can be confirmed by ring count.
In the figure: a 1908 light ring is found in the CAT horizontal section of a spruce that survived the Tunguska catastrophe. (see paper pdf and Figure).