"Crater Lake caldera formed 6,845 carbon-14 yers BP."
I think the date you are using might be under the old carbon-14 datings, not the newer callibration which has pushed these dates back a number of hundred years earlier. Haraldur Sigurdsson in his "Encyclopedia of Volcanoes," 2000, says that Crater Lake is about 7,500 year old, and that is the age that I was using when I stated my idea in the previous comment. Now I will look at the link you so kindly provided.
When that term (carbon years) is used, it refers to the so-called uncalibrated dating; the so-called calibrated scale uses wiggle matching to try to correspond to established sequences in (for example) tree rings.