February 7, 2020
3:00pm in PLS 1140
Doug Hemingway from Carnegie
Magnetic anomalies and the color of the Moon—insights from lunar swirls

Abstract: An enduring mystery since Apollo is that, in spite of the Moon's lack of a global magnetic field, the surface is nevertheless dotted with regional magnetic fields strong enough to be detected from orbit. Did the Moon once have an intrinsic global field that magnetized parts of the crust but has since decayed away? Adding to the puzzle, many of these magnetic anomalies are accompanied by enigmatic optical anomalies known as lunar swirls, which may arise as a result of local variations in space weathering—the poorly understood processes by which the optical properties of airless bodies change over time. Here I will show that we can use swirls to tell us about: 1) the structure of near surface magnetic fields and the characteristics of the underlying magnetic sources; and 2) the optical effects of solar wind weathering and the resulting systematic latitudinal variation in the color of the Moon. These results have implications for the origins of the Moon's crustal magnetic anomalies, the nature of space weathering processes, and the way spectral observations are interpreted across the lunar surface.

February 14, 2020
3:10pm in PLS 1140
Ellen Syracuse from LANL/DOE
Probing temporal changes in the shallow subsurface using ambient seismic noise (and, life at a national lab)

Abstract: In recent years, a dramatic  and unsustainable mining of  groundwater, our largest  fresh water source, has taken  place in the western US, with  depletion rates currently at  their highest. Paired with  periods of drought in as much  as a third of the contiguous  US, the monitoring of  groundwater resources is  increasingly important. How  do aquifers respond to  stresses such as increased  withdrawal rates and droughts? What does the end of a drought mean for groundwater availability? We employ  temporal monitoring of  ambient-noise-based  horizontal-to-vertical  amplitude measurements (H/V, or ellipticity) to probe  changing conditions within  the shallow subsurface. We present results of this analysis for southern California for the past 20 years. Notable features  observed are long-term  changes in H/V interpreted to  be groundwater signals and seasonal variability in H/V from a variety of sources. Come and also learn about other potentially surprising types of research geoscientists perform at Los Alamos National Lab.

February 21, 2020
3:10pm in PLS 1140
Joyce Sim from Carnegie DTM
Melt focusing beneath mid-ocean ridges: implications for the lithosphere asthenosphere boundary

Abstract: At mid-ocean ridges, oceanic crust is emplaced in a narrow neo-volcanic region on the seafloor, whereas basaltic melt that forms this oceanic crust is generated in a wide region beneath as suggested by a few geophysical surveys. The combined observations suggest that melt generated in a wide region at depths has to be transported horizontally to a small region at the surface. We present results from a suite of two-phase models applied to the mid-ocean ridges, varying half-spreading rate and intrinsic mantle permeability using new openly available models, with the goal of understanding melt focusing beneath mid-ocean ridges and its relevance to the lithosphere asthenosphere boundary (LAB). Three distinct melt focusing mechanisms are recognized in these models: 1) melting pressure focusing, 2) decompaction layers and 3) ridge suction, of which the first two play dominant roles in focusing melt. All three of these mechanisms exist in the fundamental two phase flow formulation but the manifestation depends largely on the choice of rheological model. The models show that regardless of spreading rates, the amount of melt and melt transport patterns are sensitive to changes in intrinsic permeability, K0. Geophysical observations place the LAB at a steeper incline as compared to the gentler profile suggested by modeling efforts. The decompaction melt-rich layer roughly follows and itself can define the lithosphere-asthenosphere boundary (LAB), which without the melt layer, would be along the temperature dependent rheological and freezing boundaries. Melting pressure focusing is the only focusing mechanism that can focus melt before reaching the typical model thermal LAB. The lack of the decompaction layers in the geophysical observations hint at the possibility that melting pressure focusing could be significant, which could provide constraints for mantle rheology, permeability and the lithosphere-asthenosphere boundary.

Watch it on YouTube

February 28, 2020
3:10pm in PLS 1140
Jacob Richardson from NASA Goddard Space Flight Center
Exploring volcanoes in Central Iceland as Analogs for Planetary Environments

Abstract: Volcanoes are found on all planetary bodies larger than Ceres. Understanding how they erupted enables us to understand the geologic past of a planet and its current distribution of materials at or near the surface. My team has investigated two neighboring volcanoes, Holuhraun and Askja, in central Iceland to survey eruption deposits that are similar to deposits we observe on Mars and the Moon. The 2014-5 Holuhraun eruption produced the most recent flood lava on Earth and its largest source vent is actively degrading. We have monitored this degradation since 2015 to characterize how different volcanic materials and landscapes change over time. Askja deposited blankets of tephra over snowfall in 1875 and 1961. We have surveyed the remaining ice deposits with ground penetrating radar to improve our ability to identify buried ice during future missions to planetary surfaces.

Watch it on YouTube

The coordinator for the Colloquium Series is Dr. Mong-Han Huang. You can contact him at mhhuang@umd.edu.
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