This post was written by Abby Rivin, 2011 Mono Lake Intern.
If you own a shovel and you like to dig, then you should consider becoming a geomorphologist. Geomorphologist Scott Stine has been digging holes in the Mono Basin since 1979. Last week during the second presentation in the Mono Lake Committee’s series, Refreshments with Refreshing ‘Ologists, Scott discussed the volcanic history of Mono Lake’s islands.
By digging holes, Scott can date different features of Paoha and Negit islands. Digging holes exposes tephra layers, or volcanic ash deposits, underneath the surface of the ground. These layers of tephra are isochrones, which means they are timelines in the stratigraphic record.
When the Mono Craters erupted 600 and 1,200 years ago, they spewed volcanic ash all over the Mono Basin and beyond—even as far as Yosemite Valley! This ash settles and, over time, forms a tephra layer. The ash from the different explosions is distinguished by a diagnostic coarse layer. The 600-year-old ash has this coarse layer at its base, whereas the 1,200-year-old ash has this layer in the center of the tephra layer. If a feature of Negit Island has the 600-year-old ash but not the 1,200-year-old ash, then it is less than 1,200 years old but older than 600.
Scott uses many forms of evidence along with tephra to reconstruct the geologic past of the Mono Basin. For example, different shorelines from the natural changing levels of Mono Lake in the past leave a mark on the soft sediments of Paoha Island and even the volcanic rock of Negit. When Scott analyzes these shorelines or tephra in the Mono Basin, he is reconstructing the recent past. Geologically speaking, the Mono Basin is brand new. If you are interested in geology, come explore this incredibly dynamic place.
Please join us at the Mono Lake Committee for the next Refreshments with Refreshing ‘Ologists with biologist Sarah Dalrymple, who will be talking about the interaction between prescribed burns, Jeffrey pines, and ants, on Wednesday, August 24th at 4:00pm.