Ross Chimneys 7. Small spatter vents of upper Ross Chimneys form part of the Black Crater-Ross Chimneys basalt flow (map unit bbr) that erupted about 3,000 years ago in the northern part of Lava Beds National Monument. The numerous spatter vents are aligned along a north-northeast trend. View is south toward the upper part of Medicine Lake volcano. Photograph by Julie M. Donnelly-Nolan.