This is still a small number compared to the original blast in 1980. Over ten million trees were blown into the lake.
Since then some were taken out for lumber and some have sunk to the bottom and began to petrify. Most of the trees that have sunk had the root ball still attached and have planted themselves standing up on the bottom.
So what you have is a forest of trees that is at the bottom of the lake that is petrified, (or well on its way) all in 28 years.