I'd like to ask another Mt. St. Helen question, since the first one was obviously too hard to answer.?

When I went to school, I was taught that it took thousands of years for wood to petrify. In fact, that was one of the ways you could tell that this was an acient fossilized speciment. But up in Mt. St. Helens, 175 sq. miles of forest was leveled, and trees up there petrified years ago. How is that possible?