Dee Wright Observatory, Oregon

12. Little Belknap and Belknap Craters
View from the Observatory

Focal point of a long-continued and complex episode of Holocene basalt and basaltic andesite volcanism. The broad shield which fills the northwest view is 5 miles in diameter; it is estimated to be 1,700 feet in maximum thickness and 1.3 cubic miles in volume. The volcano probably contains a core of cinders which interfingers with peripheral lavas and whose surface expression is the summit cone. Basaltic andesite issued from vents at the north and south bases of the cone approximately 1,500 years ago. Lava poured 12 miles to the west and ash was ejected from the northernmost of two summit craters. The main bulk of Belknap ash, which has been traced over an area exceeding 100 square miles, was ejected earlier from a larger south crater. Still earlier lavas were basaltic and moved eastward 7 miles from their vents.

Little Belknap - A subsidiary shield volcano, built 2,900 years ago on the east flank of the larger crater.