The Sierra crest, Panum Dome, and Mono Lake, California by ahochstaedter

Panum Dome is a ~700 year old rhyolite dome that erupted though an earlier-formed explosion pit. Debris from the earlier explosive event was deposited in an explosion ring that encircles Panum Dome itself. The explosion ring is composed of ash, pumice fragments, and cobbles of Sierra granite and metamorphic rock. The high proportion of non-magmatic material indicates that the explosion was probably phreatic in nature involving magma-heated water that reached its flash point and caused an explosion. The dome itself is composed of rhyolite and contains banded textures. Whereas spires are visible on the left side of the dome, much of the dome is covered with rhyolitic rubble.

In front and slightly to the right of the Panum Dome explosion ring lies the remains of another rhyolite dome. This one is called Pumice Pit Dome.

Beyond Panum Dome lies Mono Lake with its two islands, the dark colored Negit Island and the lighter colored Paoha Island. Negit Island is a dark dacite cinder cone, whereas Paoha Island is composed mostly of light colored lake sediments that have been pushed up by magmatic activity. On the north side of Paoha Island, visible towards the right in this image, are recent dacite and rhyolite lavas. The most recent uplift and volcanic activity occurred about 250 years ago.

To the left of Panum Dome lies the Sierra range front and a few peaks that comprise the Sierra crest or lie just to its east. From left (south) to right (north), major peaks inclue Parker, Lewis, Gibbs, Dana, Warren, and Dunderberg. Prominent glacial moraines emanate from Bloody Canyon and Lee Vining Canyon. The relatively flat surfaces on the landscape between the range front and Mono Lake are ancient shorelines of Lake Russell, the large glacier-fed lake that filled this basin in Pleistocene times.

More information about Panum Dome and the Mono Basin can be found in David Jassey’s on-line field guide: geology.csupomona.edu/docs/sierra.html Excellent guidebooks by Sharp and Glazner, “Geology Underfoot in Death Valley and Owens Valley”, and Glazner and Stock, “Geology Underfoot in Yosemite National Park”, provided much of the information presented here.