Geologic History
The Mono Basin lies along the Sierra-Mono
fault. The fault is the boundary between the Mono Basin and
the Sierra Nevada Mountains to the west of Mono Lake. The region
to the west of the fault is progressing in a northerly direction,
while the eastern part is heading south. Over the past 4 million
years, this tectonic movement has thrust the mountains to the
west 4000 feet upward, while the basin to the east has been forced
downwards about 6000 feet. At the same time, the basin has been
filling with as much as 3000 feet worth of sediment from the
erosion of the ancient Sierra Arc Volcanoes. This has created
an elevation difference of 7000 feet across the fault.
At 40,000 years of age, the volcanic chain that extends to the
north and south of Mono Lake is the youngest or one of the youngest
volcanic mountain chains in North America. Panum Crater is the
site of the last eruption in the chain. This eruption occurred
less than 700 years ago. The volcanoes within the chain are
more accurately described as plug-dome volcanoes, making a reference
to the lava-based dome shaped formation found within the crater
of the volcano.
Two sizeable islands have formed in the
lake as a result of volcanism. The smaller island to the north,
Negit, first erupted 1,600 years ago and has been active as recently
as 270 years ago. Negit Island has a classic cinder cone shape,
which contrasts with the lakebed surface of Paoha, the larger
white island. Paoha was formed as a result of magma flows that
forced as section of the lakebed upwards. It has yet to have
a full-scale eruption.
Monolake
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