Come back when you learn to comprehend, idiot.<<sigh>> I'll take a stab at it, Jimmy.
The "1mm varve" thickness is the AVERAGE thickness accumulated during an AVERAGE, UNEVENTFUL year.
If there is an EXTRAORDINARY EVENT.....say, ummmm A FRICKIN VOLCANO that is erupting nearby, it will deposit MUCH MORE sediment into the lake, and will result in a MUCH THICKER LAYER between the annual varves.
In the case you're describing, many 'uneventful' years were interrupted by a volcano that deposited a bunch of ash that resulted in volcanic glass when it cooled down, and compressed under subsequent 'uneventful' years sediments.
My DOG could pick this up after first read.
The piece itself claims that each varve was 1 millimeter and that the all volcanic ash layer was 1 centimeter thick, meaning science was claiming it took more than 10 years to create that formation, you fruking moron.