DeFord Lecture Series

DeFord Lecture Series Speaker Schedule

The DeFord (Technical Sessions) lecture series has been a requirement and a tradition for all graduate students since the late 1940s. Once the official venue for disseminating DGS graduate student research, the DeFord Lecture series is now the forum for lectures by distinguished visitors and members of our community. Faculty and researchers from the Jackson School have invited prestigious researchers from around the world to present a lecture in this series. This is made possible only through a series of endowments, such as those funding past Distinguished Lectures.

The list below shows all the scheduled talks this semester. If you would like to meet with any of the speakers, please contact them or their hosts directly.

DeFord Lecture Series 2022-23 Speaker Schedule

All talks are Thursdays from 4-5PM (CST) in the Boyd Auditorium (JGB 2.324).  Lectures will be recorded, and most past lectures are posted on the Jackson School YouTube channel.

Date Speaker/
Oct 6 Brad Foley, University of Pennsylvania Planetary interior controls on the habitability of rocky exoplanets
Abstract: An essential factor for the habitability of rocky exoplanets is climate regulation via the carbonate-silicate cycle. Without such regulation, uninhabitably hot or cold climates can form, even for planets lying within their host star’s habitable zone. The planetary interior plays a critical role in driving the carbonate-silicate cycle, as it controls how volatiles are cycled between surface and interior over time. I will explore these links between interior dynamics and climate evolution considering the role of a planet’s tectonic state, thermal evolution, and area of exposed land. While it has long been thought that plate tectonics might be essential for the carbonate-silicate cycle to regulate climate, I show that the same stabilizing feedbacks can also operate on planets lacking plate tectonics. However, these results point to the importance of active volcanism, which is in large part controlled by the budget of radiogenic elements (U, Th, and K) a planet acquires during formation. Radiogenic heat producing element (HPE) abundances are not directly measurable in other planets, but estimates can be made based on the composition of stars planets orbit. I therefore use measured HPE abundances in stars to determine the likely range of heat budgets for rocky exoplanets and estimate how long they can stay volcanically active in a stagnant-lid regime. The results show many known exoplanets, including the Trappist system, may be too old to still be volcanically active today. Finally, I discuss the role of exposed land in sustaining habitable surface conditions. Whether sea floor weathering provides a climate regulating feedback, like weathering of exposed land, has been long debated. Based on recent estimates of the seafloor weathering rate and its dependence on temperature, ocean pH, and spreading rate, I show that planets lacking exposed land can potentially regulate their climates better than planets with land. This result opens up the possibility of habitable climates on waterworld planets.
Oct 13
No lecture (GSA)
Oct 20 Elowyn Yager, University of Idaho It’s not always rainbows and butterflies: vegetation influences on rivers beyond sediment deposition and meander formation
Abstract: Vegetation is ubiquitous in river and delta systems and is often used to restore river channels with the assumption that vegetation addition will cause sediment deposition and stabilize channel banks. Uncertainties remain as to whether vegetation actually enhances sediment deposition because of the competing influences of vegetation drag and vegetation induced turbulence. Vegetation can also cause significant spatial variability in deposition/erosion that complicate common correlations between vegetation and channel planform. We use laboratory experiments at a wide range of spatial scales (stem to river reach) to understand the mechanics of turbulence and sediment transport through vegetation, and the impact of vegetation and flow hydrographs on channel morphology. We demonstrate that complex feedbacks between flow hydraulics, channel morphology, and sediment transport during flow hydrographs control whether vegetation causes local deposition or erosion. The role of vegetation in promoting a certain type of channel planform (e.g., meander) may depend on vegetation location within the channel and the upstream sediment supply.
Oct 27
Jessica Guo,
University of Arizona
Sensitivity of plant water use to a changing environment
Abstract: The global carbon and water cycles are inextricably linked through plant stomata, as water loss is an inescapable consequence of photosynthesis. Characterizing the sensitivity of plant processes to environmental controls becomes even more urgent as climate warms and precipitation regimes change. As a dryland plant ecophysiologist, I study the sensitivity of water use strategies to seasonal variability and the consequences for ecosystem productivity. In well-watered riparian ecosystems, desert trees differ in their stomatal sensitivity to cumulative atmospheric dryness, which is associated with differences in xylem anatomy. Among dryland species such as creosote bush and Utah juniper, regulation of midday water potential shifts rapidly to allow for greater productivity under episodic precipitation. Broadening our understanding of plant water use strategies as temporally dynamic has the potential to explain why dryland ecosystems are largely responsible for high inter- and intra-annual variability in the terrestrial carbon cycle.
 Nov 3
Tim Lyons,
University of California, Riverside
 TBD  Sun  
Nov 10
Bruce Fouke,
University of Illinois
TBD Kerans
Nov 17
Barbara Carrapa,
University of Arizona
Rising from the ashes: marine and continental feedback responses to Andean volcanism and Miocene climate

Abstract: The late Miocene is a critical time within the generally cooling trend of the Cenozoic, characterized by a warmer climate than today, shifts in global geo- and bio-chemistry and sea surface temperatures, and modern-like atmospheric pCO2. Although the cause(s) of these shifts remains unresolved, we show a strong correlation between Andean volcanism and diatom occurrence and abundance. This combined with increased Si flux from the Amazon river into the Atlantic starting at ~9Ma, and increased aridity, supports a connection between an increased flux of nutrients (Fe, Si) to the oceans in the Late Miocene that could have led to increased marine primary production associated with the Late Miocene Carbon Isotope Shift (LMCIS), the Late Miocene Biogenic Bloom (LMBB), and, through an enhanced biological pump and increased organic carbon burial, Late Miocene cooling. Peak late Miocene magmatism in the Central Andes coincides with global SST cooling. Peak Andean magmatism also correlates with a sharp increase in marine megafauna extinction rates. We suggest that the combination of Andean volcanism, climate and tectono-morphic regime contributed to ocean fertilization, enhancement of the biological pump, biogenic carbon burial, CO2 drawdown, and cooling in the last ca. 12 Ma, which disrupted marine ecosystems, especially in coastal waters, and contributed to the extinction of marine megafauna and the establishment of modern marine communities.

Dec 1
Isaiah Bolden,
Georgia Tech
TBD  Lassiter/
Dec 8
Jonathan Ajo-Franklin,
Rice University
TBD Fomel
Sep 1
Andrew Moodie, Jackson School of Geosciences Leveraging natural delta land-building processes to enable coastal landscape sustainability
River deltas provide many societal benefits, and sustainability of these landforms may be impacted by human modification and global climate change. For example, anthropogenic river control structures inhibit natural sediment dispersal that is necessary to sustain coastal lands in the face of rising sea levels. Declining land area strains human welfare by way of reduced ecosystem services, damaged cultural connections, and hindered economies. To rehabilitate drowning coasts in the Mississippi River delta (Louisiana, USA), engineered river diversions are expected to restore sediment dispersal and promote land growth, but a limited understanding for long-term natural deltaic landscape building processes limits our ability to optimally place diversion structures in space and time. In this presentation, I will demonstrate how reduced-complexity numerical modeling informs natural delta land building processes, supports quantifying societal benefits and costs of diversions, and identifies hazards to land building diversions.
Sep 8



Marc Hesse,

Jackson School of Geosciences

Mass transport through Europa’s ice shell and the habitability of Europa’s internal ocean
Jupiter’s moon Europa is thought to have an ocean beneath its ice shell and the habitability of this internal ocean may depend on the availability of redox gradients. Downward transport of radiolytic materials produced at the surface through the ice shell likely sets the flux of oxidants into the ocean. Astronomical observations suggest that Europa’s near surface regolith contains 1014 to 1018 mol of O2 and likely other oxidants. Today I will discuss recent work in my group on three different potential transport mechanism for the oxidants through the ice shell: Convective overturn, brine percolation and impacts. Due to the strong temperature dependence of the thermal conductivity the ice-shell has very thick conductive lid that prevents the transport of oxidants through the ice by convective overturn. A second process is the drainage of large volumes of near-surface brines beneath chaos terrains. I argue that these brines percolate readily and can potentially transport surface-oxidants into the ocean at a rate of 106 to 1010 mol/yr. Finally, I discuss the effect of impacts on mass transport through the ice. We have shown that impacts do not need to penetrate the ice shell to generate vertical mass transport. The foundering of impact generated brines though the ice provides a potential mechanism to bring oxidants into the ocean at a rate of 101 to 105 kg/yr. Assuming sufficient production of reductants due to weathering of Europa’s seafloor, our estimated oxidant fluxes are deemed sufficient to sustain primitive life in Europa’s internal ocean. Our simulations also imply that large volumes of near surface brine are not be stable in long timescales, a hypothesis that is testable by NASA’s Europa Clipper mission.

Sep 13



Ashley Matheny, Jackson School of Geosciences
Sensing, synthesizing, and integrating plant ecohydrology for understanding and predicting land-atmosphere feedbacks in response to environmental extremes
My research explores how forests respond to different stressors across multiple dimensions and scales. This is important because vegetation provides a critical nexus between the subsurface, biosphere, and atmosphere through the mediation of the exchange of water, carbon, and energy. Plants respond dynamically to local microclimates at both short and long time scales via mechanisms ranging from physiological behaviors, such as stomatal closure, to acclimation and adaptation. These responses influence land-atmosphere fluxes directly and are therefore crucial to understanding and predicting Earth system responses to a changing climate. For example, how will ecosystems respond to the coupled extremes of high temperatures and water limitations? By exploring water-use dynamics and photosynthetic rates in trees near the furthest edge of their range limits, we gain insights into how these species will respond to predicted climate shifts in the coming decade. Likewise, through the development of a mechanistic understanding of how trees manifest stress responses, we can better predict the complex feedbacks to carbon, water, and energy fluxes that subsequently develop. In this seminar, I will discuss the work conducted by my team, which is tightly integrated with my graduate and undergraduate education and research programs, to develop novel observational systems and advanced field datasets in conjunction with holistic interpretation methods that facilitate direct data incorporation into multiple model systems leading up to our newest directions and future research.
Sep 15



Daniella Rempe, Jackson School of Geosciences
How forests connect the solid earth to its atmosphere
Earth’s crust is penetrated by plant life. Tree roots commonly extend into bedrock where they exchange water and carbon with the atmosphere leading to mineral transformations. This has consequences for the availability of Earth’s freshwater resources and how these resources evolve over time and space with climate change. In this talk, I describe new insights about how forests interact with underlying bedrock. These insights are gleaned from novel sampling systems, geophysical tools, and remote sensing capabilities that allow us to document how hydrologic and biogeochemical processes in the root-zone manifest at larger scales. I will focus on observations from recent droughts in the western US that motivate a new framework for incorporating bedrock properties into projections of ecosystem and streamflow response to drought.
Sep 22
Liannie Velazquez Santana, Jackson School of Geosciences
Revealing magmatic and tectonic processes through a multifaceted study of the monogenetic volcanic record of the Eastern Bolivian Altiplano
Abstract: The volcanic products of continental arc volcanoes provide comprehensive insights into the complex nature of magmatic systems. For example, current understanding supports the presence of complex, dynamic transcrustal magmatic systems (TCMSs) that consist of interconnected regions of magma storage where liquid-poor, crystal-rich mushes exist and variably interact. However, the extent to which these petrogenetic pathways affect storage, differentiation, and final eruption (or emplacement) of magmas at different crustal regions within the magmatic system remains challenging to address. In this talk, I will address this through a study of andesitic-dacitic lavas, hornblendite cumulates, and crustal xenoliths from the Pampa Aullagas and Quillacas monogenetic volcanic centers on the Bolivian Altiplano, Central Andes. Through this work, I use a multifaceted analytical approach to 1) characterize the magmatic and crustal components of TCMSs and 2) constrain the tectono-magmatic processes and petrogenetic pathways of magmas at varying timescales and stages within TCMSs. 
Sep 27
David Goldsby, Department of Earth and Environmental Science,
University of Pennsylvania
Mechanisms of Rate and State Friction: Insights from Atomic Force Microscopy, Nanoindentation, and Atomistic Simulations
Abstract: In spite of their widespread use in earthquake models, rate and state friction ‘laws’ still lack a robust physical basis.  Without knowledge of the underlying physical/chemical mechanisms of rate and state friction, there is uncertainty in extrapolation of these equations beyond the relatively limited range of conditions explored in the experiments that provide their basis. To explore the contact-scale mechanisms of rock friction, we are conducting ‘single-asperity’ experiments using atomic force microscopy and nanoindentation coupled with atomistic modeling and simulations.  Here I will attempt to merge results of these nano- to micro-scale single-asperity experiments and simulations with those from friction experiments on rocks to help constrain the mechanisms of rate and state friction.