The bulk of my research is carried out through the development and implementation of quantitative and numerical analyses, two examples of which are shown below:
1) A 2-D numerical model I developed to simulate convective cooling of impact melt deposits on the Moon (a description of this research project, and the motivations behind it, can be found below).
2) A 3-D numerical model which simulates the growth of permafrost (referred to in the video as the cryosphere) around Don Juan Pond, a relatively small hypersaline lake within the Antarctic Dry Valleys (a description of this research project, as well as the motivations for it, can be found below).
Martian Hydrology and Glaciology
The surface of Mars contains a wide array of evidence which suggests a relatively complex history of hydrological activity on the planet. The valley networks and outflow channels (examples of which are shown above) are of particular interest, as these features are interpreted to have originated through fluvial activity. The valley networks are branching systems of valleys, typically a few kilometers in length, but with some systems having integrated lengths of up to approximately 5,000 kilometers. The abundant presence of these features in the oldest terrains of Mars has commonly been cited as evidence for a more intense period of diffuse precipitation-derived fluvial activity on early Mars. In contrast, the outflow channels are a more limited population of isolated channels, originating from point sources and lacking significant tributaries, which are found primarily in terrains younger than those that host the valley networks. The outflow channels are far larger than the valley networks, typically thousands of kilometers in length, and up to hundreds of kilometers in width. Outflow channels generally appear fully-sized and are thought to have formed by outburst floods, involving the release of tremendous quantities of water. The mechanisms responsible for the formation of the valley networks and outflow channels remain in question. Recent global climate models have been unable to reproduce the warm and wet conditions required to sustain the precipitation and groundwater recharge needed to form valley networks and outflow channels.
My research efforts in this area focus on the exploration of alternative mechanisms by which the valley networks and outflow channels may have formed under cold and icy conditions in order to reconcile their presence with the predictions of the global climate model studies. The mechanisms I investigate involve the interaction of volcanic processes with ice sheets that are predicted by global climate models to have accumulated across high-elevation areas on early Mars. Glacial features are known to form under present-day conditions on Mars (see below for an example), and possible evidence of lava-ice interactions is also preserved on the surface of Mars today (Maars/rootless cones, shown below). It is likely that these interactions also took place on early Mars due to the contemporaneous accumulation of regional ice sheets and widespread intense volcanic activity. Assessments of these alternative formation mechanisms are performed through the implementation of quantitative models to outline estimates for melting rates and volumes which are compared against those required to form the observed fluvial features.
- Weiss, D.K., Head, J.W., Palumbo, A.M., and Cassanelli, J.P., (2017). Extensive Amazonian-Aged Fluvial Channels on Mars: Evaluating the Role of Lyot Crater in their Formation. Geophysical Research Letters, 44(11), 5336-5344, doi:10.1002/2017GL073821
- Cassanelli, J.P., and Head, J.W., (2016). Lava Heating and Loading of Ice Sheets on Early Mars: Predictions for Meltwater Generation, Groundwater Recharge, and Resulting Landforms. Icarus, 271, 237-264, doi:10.1016/j.icarus.2016.02.004
- Cassanelli, J.P., and Head, J.W., (2015). Firn Densification in a Late Noachian "Icy Highlands" Mars: Implications for Ice Sheet Evolution and Thermal Response. Icarus, 253, 243-255, doi:10.1016/j.icarus.2015.03.004
- Cassanelli, J.P., Head, J.W., and Fastook, J.L., (2015). Sources of Water for the Outflow Channels on Mars: Implications of the Late Noachian "Icy Highlands" Model for Melting and Groundwater Recharge on the Tharsis Rise. Planetary and Space Science, 108, 54-65, doi:10.1016/j.pss.2015.01.002
Geology and Petrology of Lunar Impact Melt Deposits
Large impact events are known to generate significant volumes of molten material through shock-heating of the target structure, as well as the impactor itself. Given the population of large impact structures on the Moon, and the cumulative volume of melt produced by these events, this suggests that a substantial portion of the lunar crust may be comprised of impact melt-related materials. Following creation and emplacement, significant changes in the composition of the impact melt can occur during cooling and solidification. Thus, understanding the geologic nature and evolution of impact melt deposits is important for a complete understanding of the geology of the lunar crust. In order to understand the geologic and petrologic evolution of lunar impact melt deposits I have modeled the physical and thermal processes which drive cooling and crystallization (an example of the analyses I employ is shown in the first section). Results of these analyses are used to derive predictions for the compositional and structural nature of impact melt deposits. These predictions are used to generate structural models of the basins which are assessed through forward gravity modeling and comparison to orbital remote sensing data.
- Cassanelli, J.P., and Head, J.W., (2016). Did the Orientale Impact Melt Sheet Undergo Large-scale Igneous Differentiation by Crystal Settling? Geophysical Research Letters, 43(21), 11156-11165, doi:10.1002/2016GL070425
The Hydrology of Don Juan Pond, Antarctica
The McMurdo Dry Valleys in Antarctica represent one of the most extreme environments on Earth. Contained within this hypothermal, hyper-arid, polar desert is the Earth's most saline body of water, Don Juan Pond. Don Juan Pond is a relatively small, shallow, calcium chloride-dominated lake situated in the South Fork of Wright Valley in the McMurdo Dry Valleys. The hyper-saline waters of Don Juan Pond allow the lake to remain ice-free, even during the Austral winter, when air temperatures drop as low as -50 C. As a result, Don Juan Pond represents a unique hydrological system. In addition, the hypo-thermal, hyper-arid environment of the Don Juan Pond basin is the closest know terrestrial analogue to the environments predicted to characterize early Mars. Thus, the Don Juan Pond basin provides an important analogue site for the study of hydrologic processes under these unique environmental and climatic conditions, and may contain valuable insights into the hydrology of early Mars.
Integral to the unique hydrological system of the Don Juan Pond basin is the thick and continuous permafrost layer expected to dominate the subsurface of the region. Despite considerable study, no consensus has been reached on the nature of the permafrost structure in the Don Juan Pond basin. Questions remain as to whether water and salts are supplied to Don Juan Pond by the upwelling of deep groundwater through an ice-free portion of the regional permafrost, or are provided by inputs from surficial runoff and melting while Don Juan Pond remains isolated from the deeper regional groundwater system by an underlying zone of continuous permafrost. To address these fundamental questions I have implemented numerical thermal models (shown in the first section) to simulate the growth and evolution of the continuous permafrost within the Don Juan Pond basin in order to derive predictions for the permafrost structure within the basin and for the origin of Don Juan Pond.
Impact of Road Salt on the Groundwater Quality of Connecticut
Salt and sand are liberally applied to the road ways of the state of Connecticut during the winter season as de-icing agents. I studied the impact of this practice, from its inceptions around 1940 to the present, on the state's groundwater quality through a state-wide analysis of temporal and spatial trends in groundwater chloride concentrations (a proxy for total salt content). The figure above is an example of the water quality maps that were produced to perform these analyses. This particular map was produced using water quality data from 1977-1978 and shows the distribution of chloride concentrations within groundwater across the state of Connecticut at that time. The state-wide analysis just described was supported by local-scale field investigations involving annual monitoring of temporal and spatial trends in groundwater salinity in local water quality monitoring wells
- Cassanelli, J.P., and Robbins, G.A., (2013). Effects of Road Salt on Connecticut's Groundwater: A Statewide Centennial Perspective. Journal of Environmental Quality, 42(3), 737-748, doi:10.2134/jeq2012.0319