These curved columnar joints in the Bishop Tuff are exposed in Owens River Gorge SW of Long Valley caldera in California. The 5- to 6-sided columns are about 1-3 m wide and curve downward to a common point, forming a feature known as a joint rosette. The rosettes are the site of large fossil fumaroles and often are overlain by fumarole mounds. These mounds may have formed as a result of volatiles produced when the hot Bishop pyroclastic flows overran and vaporized the ancestral Owens River.

Photo by R.V. Fisher, 1984 (University of California Santa Barbara).

Keywords: outcrop | deposit | pyroclastic flow | tuff | ignimbrite | pyroclastic density current | PDC

Long Valley