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A few sharp-eyed visitors to Hot Creek, Long Valley's bubbling and boiling geothermal drainage, have noted that a new hot water feature has popped up on on shore of the creek (first photo). While dramatic, this is a common occurrence. The locations, discharge rates, and temperatures of Hot Creek's springs often change. The larger and more vigorous springs flow from fractures in the volcanic rhyolite. When these fractures become sealed by mineral deposition, spring discharge and temperature decline, but when new fractures develop or sealed fractures reopen, spring discharge and temperatures can increase suddenly. 

Hot Creek is a surface exposure of the much bigger underground hydrothermal system in Long Valley. Melted snow from the highlands around the caldera infiltrates deep enough below the surface to reach the heat of cooling magma. Sometimes it can reach temperatures of 430F (220C). This hot water is less dense and rises along fractures and faults in the overlying rhyolite to discharge in Hot Creek (second photo) and around Crowley Lake. Sometimes it is even pressurized enough to create small geysers, though these are mostly temporary features.

Because of the dynamic nature of Hot Creek's thermal features, it is an extremely dangerous spot and visitors should never go beyond posted fences and signs. Even water that seems cool one moment could become scalding hot and deadly in just seconds! That's why, tempting as the steaming water might be, Hot Creek is best enjoyed from a distance. 

Read more about Hot Creek at https://pubs.usgs.gov/fs/2007/3045/fs2007-3045.pdf