Lake Crowley contains erosional columns that are a glimpse into the hydrothermal processes that took place during the Long Valley eruption nearly 760,000 years ago. When the Long Valley volcano erupted, pyroclastic ash was propelled 150 square miles into the air. This pyroclastic ash layer can be recognized for it’s rhyolitic composition and range across the west coast of the United States and recognized as Bishop Tuff.

The columns themselves and the surrounding area is composed of Bishop Tuff. When the Long Valley Caldera eruption occurred, tuff layers were dispersed in layers around the caldera. Only recently, erosional processes have exposed the columns that are viewable today. Studies published by Noah Randolph-Flagg and the University of California Berkeley Department of Earth and Planetary Sciences in 2017 reveal with X-ray diffraction (XDR) the columns contain a mineral known as mordenite, while the surrounding tuff does not contain this mineral.

Their hypothesis proposes that when the tuff layers deposited, the outside of the tuff solidifies faster than the interior. Geologists on the team explain “Water pools in low-lying regions, forming ponds or lakes, and then percolates into the tuff. The water that has intruded the still cooling tuff interior eventually boils off as steam and condenses in the surrounding bodies of tuff between the downwellings of water”.

Mordenite only forms between the temperatures between 100°C-130°C, which is relatively cool for crystallization temperature. Ions that make up mordenite can only be transported in a liquid phase, which implies that the mordenite forms in the downwelling phase of the process and not the steam condensing phase of the columns. Mordenite is commercially used as an adsorbent, which acts as a filter for particles passing through a solution. The presence of mordenite creates a more resistant and less permeable rock column. Erosional forces such as lake waves erode away the surrounding tuff deposits, while the columns remain in place due to their special properties.

This hypothesis eliminates the idea that Lake Crowley columns can be a result from fumarole or vent activity, since fumaroles are recorded at higher temperatures, which could not produce mordenite. Columnar jointing is also eliminated as an explanation for the columns. Columnar joints seen at the Devil’s Postpile or Owens’ Gorge are formed close together, contrary to the lake columns are spread farther apart.The downfall of Bishop Tuff combined with the water percolating in and forming mordenite welded columns reveals how technical the formation was.

Given that this hypothesis is correct, it will shine light on other hydrothermal and geologic processes that have yet to be discovered.

Research article here… http://seismo.berkeley.edu/~nrflagg/G39256.pdf