Don Rodbell

Erika, Gabriella, and I near the end of a two week raft trip through the Grand Canyon

This past year saw my field research return to southern Ecuador—to Cajas National Park to better understand the role of the El Nino Southern Oscillation on sedimentation in the region’s lakes. Cajas National Park has one of the highest densities of lakes in the world, it spans both the eastern and western sides of the Continental Divide, and it is less than 150 km east of the Bay of
Guayaquil, which experiences pronounced changes in sea surface temperature during El Niños. During the summer of 1995, then students Adam Goodman ’96 and Jeff Nebolini ’96, joined me to study the glacial geology of the region. We cored many lakes and discovered that some of these appeared to record El Niño storms and eruptions of the large active volcanos in northern Ecuador. Since our early publications on the region there has been a renewed emphasis on understanding the geologic history of El Nino and on our ability to predict the impact of global climate change on the amplitude and frequency of ENSO.
This year Annika Wells ’19, Grace Delgado ’14 and Sam Mark, a PhD candidate at the Univ. of Pittsburg, and I spent about three weeks in the region coring lakes. Unfortunately, Cajas National Park, though spectacular, is one of the wettest, coldest places I have ever worked! Unlike much of the tropical Andes, there does not appear to be a dry season, as it rained or snowed nearly every day. The weather coupled with steep terrain and elevations between 12,000 and 14,000 feet made for some long days. Ultimately, our field season was successful, despite the bruised and beaten condition in which we left our rental van! Grace’s family lives in nearby Cuenca Ecuador, and her parents, Maya and Hugo Delgado, were enormously helpful in virtually every logistical hurdle we faced.
The Lake Junin (Peru) drill core project was the main focus of the Core Lab over the last year, and the first batch of manuscripts are currently being written. The all-important age model, based on a combination of U/Th, radiocarbon, and paleomagnetics suggests the 100-meter-long core from Site 1 spans about 700,000 years. The record of glacial flour preserved in the core reflects the occurrence of about 8 ice ages that ap-pear to have been remarkably synchronized with the global record of glaciation in spite of very different orbital (Milankovitch) forcing.
Senior Tshering Lama Sherpa ’18 studied in detail the last two ice ages recorded in Lake Junin. Specifically, Teshering measured the grain size distribution of over 100 samples of glacial flour from the last glacial cycle. Her results indicate that during the wettest or snowiest intervals of the last ice age, inflow current velocities increased, thus depositing coarser silt
In early August daughters Erika (24) and Gabriella (21) joined me for a two-week raft trip through the Grand Canyon from Lee’s Ferry to Diamond Creek. We all found the full experience to be unforgettable. It was especially exciting to see the region’s stratigraphy, including the Great Unconformity, the Grand Canyon Supergroup, and the recent volcanics. The side valley hikes and running rapids in kayaks, some of which ended up-side down (!), were other high-lights.

Grace Delgado (’14) and Annika Wells (’19) in Cajas National Park Ecuador

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