Juvenile clast-rich layer. The basal J1 layer is the thickest layer and is comprised entirely of inflated fresh scoria that is commonly black. Scoria sags, reverse grading, and bomb horizons exist in J1 at the sites closest to the caldera, 6-8 km from the rim.
Physical volcanology of a sub-plinian and phreatomagmatic eruption at Okmok Volcano, Alaska: implications for explosive mafic volcanism
This website is supported by the U.S. Geological Survey under Cooperative Agreement Grant G19AC00060 and G19AC00171.
Mention of trade names or commercial products does not constitute their endorsement by the U.S. Geological Survey.