Fall 2020

Tuesdays at 3:30 PM

October 6, 2020

Speaker: Jane Willenbring, Stanford University

Title: Forged Signatures: Tectonic versus climatic control on Cordilleran mountain heights and Andean topographic asymmetry

Abstract: A long-standing debate in the Earth Sciences bears on the question of whether top-down erosion processes govern mountain building processes, but how do we measure the topographic signature of the climate drivers independent of tectonics? We use two natural experiments to detangle a potential signature of climate and drivers of erosion using the large latitudinal range of Earth’s orogens and their rain shadows in order to vary temperature and precipitation while holding tectonic accretion (relatively) constant. In the past decades, glacial erosion has emerged as a driving surface process controlling the heights of mountains and as the cause of accelerated erosion of mountains in mid-latitudes on Earth. Here, we present topographic and erosion rate data from the Cordilleran-style mountain ranges from South America through Alaska to demonstrate that the distribution of mountain heights and overall mass correlate linearly with the rate of plate convergence. Given the large latitudinal range of our dataset, this should not be expected if climate governed these parameters. Thus, tectonic processes set the limits on mountain heights. In addition, coupled deformation-surface process models predict that orogenic asymmetries may be modified by dominant wind direction and erosion, i.e. the formation of orographic rainfall gradients across strike. We present data comparing the radius of curvature of the subducting Nazca slab with orogenic wedge widths of the Andes and present correlations between slab-dip and arc position to suggest that as the arc position changes with slab dip, the asymmetry of an orogenic wedge may consequently change. Given that erosion rates do not mirror rain shadows, the slab geometry must be accounted for when assessing the climatic influence on orogenic asymmetry. Possibly, climate signals may be imprinted on hillslope processes, but not erosion rate magnitude.


Host: Em Schnorr

October 13, 2020

Speaker: Briony Horgan, Purdue University

Title: The Perseverance rover: NASA's next big step in the search for life beyond Earth


Abstract: The Perseverance rover on the Mars 2020 mission launched on July 30 and is set for a rendezvous with Mars in February 2021. The rover will land in Jezero crater to search for signs of ancient microbial life and select samples for eventual return to Earth. In this talk I'll give an overview of what we know about the geomorphology and mineralogy of Jezero from orbital data, a preview of how we might test current hypotheses for the geological and astrobiological history of the region with the rover, and an example of the sample suite that we might expect to return.

Host: Rachel Maxwell

October 20, 2020

Speaker: Francis Rengers, USGS

Title: The Problem of Wildfire: How Wildfire Leads to Cascading Hydrologic and Geomorphic Hazards

Abstract: Within our solar system, Earth is the only planet that is affected by wildfires, and wildfire has been a constant presence on the planet since at least the Silurian period. However, the effect of wildfire on the earth’s surface remains relatively under-studied. Many studies of earth surface processes focus on how fluids (e.g. wind, water, ice) directly shape the earth through sediment transport. Wildfire does not directly transport sediment. However, wildfire is a remarkable catalyst for earth surface change because it alters two key landscape properties: (1) wildfire greatly increases the susceptibility for overland flow in otherwise well-drained soils, and (2) wildfire increases soil erodibility relative to similar unburned settings. Consequently, order-of-magnitude increases in erosion rates may occur during rainstorms with relatively frequent recurrence intervals. This talk will focus on typical wildfire effects in burned watersheds, with a special focus on the role of wildfire in generating debris flow and landslide hazards.


Host: Noah Finnegan

October 27, 2020

Speaker: Daniel Ibarra, UC Berkeley

Title: Drivers of hot and cold past wet states recorded by lakes in the western United States


Abstract: G.K. Gilbert’s 1890 monograph on Lake Bonneville published by the United States Geological Survey initiated over a century of research on Quaternary lakes in the American west. The continuation of this work is increasingly pertinent today with the need to test climate models used to forecast future water resources in the region as the climate warms. Importantly the presence or absence of lakes in terminal basins provide an unequivocal measure of wetness. In this work I will show that wetter conditions during both colder- and warmer-than-present periods in the past are recorded in shoreline and outcrop data from the latest Pleistocene and the middle-Pliocene. In conjunction with paleotemperature data, derived from pollen, macrofossil assemblages and carbonate clumped isotope measurements, I will show scaling relationships implying that: 1) Pleistocene lakes during glacial maxima in the northern Great Basin do not require substantial precipitation increases to explain lake shoreline extents; and 2) middle-Pliocene lakes would have required up to a doubling of precipitation in the southwest. These inferences provide quantitative targets for assessing the performance of climate model simulations of the terrestrial water cycle. In addition, I will show ongoing work associated with the application of carbonate clumped isotope thermometry and triple oxygen isotope measurement to lacustrine lake sediments in the western United States.

Host: Terry Blackburn

November 3, 2020

Speaker: Ying Fan, Rutgers University

Title: Watering the Land from Below: Groundwater Influence on the Terrestrial Environment

Abstract: Much of the water on land is groundwater, which moves through the Earth’s crust at time scales of days near the surface to billions of years kilometers down. I will focus on the shallow and actively circulating groundwater which facilitates many near-surface processes that directly influence water, energy and biogeochemical cycles on Earth. I will examine the modern-day patterns and drivers of continental water storage and drainage, and their influence on land plants such as plant rooting depths and seasonal plant water sources. Then I will pose some hypotheses on how the shallow groundwater may have functioned through the geologic past, with the last deglaciation and land plant evolution as two examples.


Host: Margaret Zimmer

November 10, 2020

Speaker: Matthew Huber, Purdue University


Host: Jim Zachos

November 17, 2020

Speaker: Elizabeth Sibert, Harvard University


Host: Matthew Clapham

November 24, 2020

Speaker: Hansi Singh, UVIC


Host: Nicole Feldl

December 1, 2020

Speaker: John Gardner, UNC


Host: Margaret Zimmer

December 8, 2020

Speaker: Aradhna Tripati, UCLA


Host: Ryan Green