the week of Sunday, January 7th, 2018

Wednesday, January 10th, 2018, Wednesday Seminar

4:10 PM, 55 Roessler
Tea and cookies at 3:45 in the aviary - (2110 EPS)

“Single-clast Be-10, landslides, and the limited landscape response to Pleistocene-Holocene climate change, Central Andes”

      – by Dr. Devin McPhillips, USGS

Erosion processes modulate the landscape response to tectonics and climate. Landslide erosion is thought to limit the growth of mountains when tectonically-driven rock uplift overwhelms the erosive power of streams. On the other hand, rates of landslide erosion are most often associated with climate, and especially precipitation, in the recent geologic record. Here, we investigate the landscape response to Pleistocene-Holocene climate change in an ice-free drainage basin in the Peruvian Andes. In order to assess the processes of erosion, as well as rates, we examine Be-10 concentrations in the individual cobbles of two populations of stream sediment, one modern and one Pleistocene (~16 ka). We show that this single-clast technique discriminates among several categories of erosion process. We then show that the Be-10 concentrations of both cobble populations are consistent with landslide erosion as the dominant process. The inferred mean rates of cobbles erosion are also similar for both populations. In order to independetly assess the rates of erosion, we also measure Be-10 concentration in amalgamated sand samples, which show a strong response to climate change in the upstream tributaries and a damped response in the downstream trunk. Comparison of Be-10 concentration in sand and cobble samples shows systematic differences, consistent with different erosion rates and processes. We interpret the results to indicate that (1) the rate of cobble erosion by landslides did not change dramatically across the Pleistocene-Holocene transition, and (2) the rate of landslide erosion is therefore not sensitive to precipitation. We propose that frequent large earthquakes are the dominant landslide trigger in this region.

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Wednesday, January 10th, 2018, Davis Science Cafe

5:30 PM, G Street WunderBar (228 G St, Davis)
Free to attend

“Why Does the Earth Have a Moon?”

      – by Sarah Stewart, UC Davis Earth and Planetary Sciences

Why do we think the Moon's formation was triggered by a giant impact? Why don't the other rocky planets have big moons? Why are the satellite systems around the giant planets so different? Come to the next Davis Science Cafe to learn the answers to these questions!

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