Geologists examining ash layers associated with the Dusty assemblag...

The orange layer just below geologist's hiking pole is the Mazama ash (about 7700 ybp). Below that are glacial deposits. Above the Mazama is about a meter consisting mostly of fine-grained tephras from Glacier Peak, capped by soil and plants. That the tephras sit directly on top of the Mazama indicates that "Dusty" eruptions commenced about 7,000 years ago. The fine grain size of the ashes probably indicates that most formed as co-ignimbrite (ash-cloud) deposits during repeated small-volume pyroclastic flows.