Ring Deposit Research Articles

The effect of the spatial variation of the evaporative flux on the deposition from a thin sessile droplet

A mathematical model for the effect of the spatial variation of the local evaporative flux on the evaporation of and deposition from a thin pinned particle-laden sessile droplet is formulated and solved. We then analyse the behaviour for a one-parameter family of local evaporative fluxes with the free parameter $n \, (>-1)$ that exhibits qualitatively different behaviours mimicking those that can be obtained by, for example, surrounding the droplet with a bath of fluid or using a mask with one or more holes in it to achieve a desired pattern of evaporation enhancement and/or suppression. We show that when $-1< n<1$ (including the special cases $n=-1/2$ of diffusion-limited evaporation into an unbounded atmosphere and $n=0$ of spatially uniform evaporation), all of the particles are eventually advected to the contact line, and so the final deposit is a ring deposit at the contact line, whereas when $n>1$ all of the particles are eventually advected to the centre of the droplet, and so the final deposit is at the centre of the droplet. In particular, the present work demonstrates that a singular (or even a non-zero) evaporative flux at the contact line is not an essential requirement for the formation of a ring deposit. In addition, we calculate the paths of the particles when diffusion is slower than both axial and radial advection, and show that in this regime all of the particles are captured by the descending free surface before eventually being deposited onto the substrate.

Miranda's Thick Regolith Indicates a Major Mantling Event from an Unknown Source

We investigated “muted” craters and scarps across Miranda’s cratered terrain. The morphologies of the muted craters are most consistent with modification by regolith deposition instead of erosion or viscous relaxation. We used three techniques to estimate regolith thickness. (1) Analysis of muted crater depth–Diameter (d-D) ratios near the South Polar Terrain Chasma indicates that regolith mantling their floors ranges from 0.3 to 1.2 km thick. Because older craters may have collected more regolith than younger craters, the true thickness may be similar to the highest estimate. (2) Analysis of crater size–frequency distributions across the cratered terrain indicates a thickness of 1.0 ± 0.2 km. (3) Analysis of a central mound within Alonso Crater indicates a thickness of km near Verona Rupes and may represent an upper limit. These results indicate that Miranda has one of the thickest regoliths in the solar system, which has important implications for Miranda’s interior thermal properties. Regolith appears to mantle some scarps within Arden but not Elsinore or Inverness, indicating that Arden may be the oldest corona, contrary to previous relative age estimates. In this scenario, the mantling event was ongoing during Arden’s formation but before Elsinore or Inverness formed. We propose three possible sources for Miranda’s thick regolith: (1) giant impact ejecta, (2) plume deposits, and (3) Uranian ring deposits. We favor the ring deposit hypothesis, which is consistent with the regolith’s large spatial extent, substantial thickness, and Miranda’s slightly spectrally blue color. Follow-up studies that rigorously investigate these scenarios are required.

Ring shells obtained from pure water drops evaporating on a soluble substrate

When a pure water drop evaporates on a soluble substrate, the final ring deposit takes the form of an inclined wall for small and flat drops and of a hollow rim for other geometries. We report here on experiments of evaporation of pure water and salty water drops on salt single crystals and inert substrates, which permit to define precisely the experimental conditions necessary to obtain such structured deposits. Their growth is not a consequence of particular thermal or chemical conditions but of the peculiar geometry of the experiments. Beside the advection of the solute toward the edge by the coffee-stain effect induced by the pinning of the drop, the role of nucleation site played by the salt substrate is a necessary condition for the hollow or inclined rim to appear. These experiments have also shown to which extent the final dryout microstructure is reminiscent of the salt crystallography. Finally, these experiments demonstrate the potentiality of the phenomenon for surface-patterning.

Simulation of deposits effect on cylinder liner and influence on new and worn compression ring of a turbocharged DI engine

Engineers and engine manufactures have known for years that piston rings account as the main source of the friction in internal combustion engines, as much as seventy-five percent in many cases. Excessive engine wear is also, very often caused by poor vehicle operation, and subsequent momentary poor lubrication.The paper presents a numerical methodology and results regarding the wear and deposition effects on an internal combustion engine piston rings as a result of engine lubrication. The deposits can lead to increment of oil consumption and emissions, reducing engine performance and fuel economy.A 2D CFD approach was implemented in order to investigate the characteristics of the top compression ring deposit formation in a diesel engine. The developed pressures, the friction force and the minimum film thickness have been investigated. The variation of the minimum film thickness for new and worn rings at piston reversals, the insufficient minimum film thickness, the thicker films of the increment of the engine speed appeared at worn ring profile in the middle of each stroke, corresponds to a worst sealing behavior due to deposit, are some of major findings of this work.The deposits investigation and hence the paper importance is crucial in combustion engines operation as well as it can covers both axial turbines and their cooling at preliminary design phase.

The Integration of Lidar and Legacy Datasets Provides Improved Explanations for the Spatial Patterning of Shell Rings in the American Southeast

ABSTRACTArchaeologists have struggled to combine remotely sensed datasets with preexisting information for landscape-level analyses. In the American Southeast, for example, analyses of lidar data using automated feature extraction algorithms have led to the identification of over 40 potential new pre-European-contact Native American shell ring deposits in Beaufort County, South Carolina. Such datasets are vital for understanding settlement distributions, yet a comprehensive assessment requires remotely sensed and previously surveyed archaeological data. Here, we use legacy data and airborne lidar-derived information to conduct a series of point pattern analyses using spatial models that we designed to assess the factors that best explain the location of shell rings. The results reveal that ring deposit locations are highly clustered and best explained through a combination of environmental conditions such as distance to water and elevation as well as social factors.

Evaporative Drying of Sodium Chloride Solution Droplet on a Thermally Controlled Substrate.

We report the evaporative drying-mediated pattern formation of dilute aqueous NaCl solution droplets on a hydrophobic surface made of cross-linked PDMS at elevated temperatures. Experiments were performed with various salt concentrations (0.08 to 2 M). Depending on the substrate temperature (TS) and initial salt concentration (Cn), a variety of unique deposition morphologies are obtained. Double salt rings are obtained at low Cn (0.08 and 0.1 M) at TS ≈ 75 °C. With the increase in Cn, the deposition morphology transforms into a single peripheral ring with a central deposition zone that is devoid of any salt deposition. On the other hand, at lower Cn and lower TS, a single outer ring deposit surrounding a central region covered with dendritic salt deposits is observed. The variation in the morphology as well as the number of rings formed is attributed to the relative strengths of the radially outward capillary-driven flow, inward Marangoni flow, and inward diffusive transport of the salt ions. A morphology phase diagram shows the collective dependence of the final deposition pattern as a function of both TS and Cn.

Deposition of Colloidal Particles during the Evaporation of Sessile Drops: Dilute Colloidal Dispersions

The deposition of colloidal silica particles during the evaporation of sessile drops on a smooth substrate has been modeled by the simultaneous solution of the Navier–Stokes equations, the convective-diffusive equation for particles, and the diffusion equation for evaporated vapor in the gas phase. Isothermal conditions were assumed. A mapping was created to show the conditions for various deposition patterns for very dilute suspensions. Based on values of the Peclet (Pe) number and Damkholer numbers (Da and Da−1), the effects of adsorption and desorption were discussed according to the map. Simulations were also done for suspensions with a high particle concentration to form a solid phase during the evaporation by using a packing criterion. The simulations predicted the height and width of the ring deposit near the contact line, and the results compared favorably to experimental particle deposition patterns.

Nanoscale Topographical Fluctuations: A Key Factor for Evaporative Colloidal Self-Assembly.

This work investigates the role of surface parameters such as the nanoscale roughness, topography, and skewness of smooth and rough Si surfaces in the shape of patterns left by evaporating colloidal droplets of spherical polystyrene particles. The droplet contact angle, colloidal deposition pattern, crack density, and rim growth velocities are experimentally evaluated for varying roughness. The contact angle and rim growth rate are found to be more for rough surfaces in comparison to smooth ones. Roughness also helps in reducing stress in the drying droplets, thereby impeding the process of crack formation as exemplified by the experimental results. The altered Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions emerging from the contribution of nanoscale roughness are theoretically evaluated for each differently rough substrate-particle combination. The forces have been calculated by considering large- and small-scale roughness parameters of the experimental surfaces. The experimental findings have been duly corroborated by theoretical estimates. Finally, it is observed that the skewness of the surface and the small-scale asperity radius bear a correlation with the DLVO forces and subsequently with the ring deposit pattern. The present understanding of the influence of surface fluctuations on evaporative self-assembly would enable one to choose the right topographic surface for particular applications.

Explosive volcanism on Mercury: Analysis of vent and deposit morphology and modes of eruption

The MESSENGER mission revealed, for the first time, conclusive evidence of explosive volcanism on Mercury. Several previous works have cataloged the appearance and location of explosive volcanism on the planet using a variety of identifying characteristics, including vent presence and deposit color as seen in multispectral image mosaics. We present here a comprehensive catalog of vents of likely volcanic origin; our classification scheme emphasizes vent morphology. We have analyzed the morphologies of all vents in our catalog, and recognize three main morphologies: “simple vent”, “pit vent”, and “vent-with-mound”. The majority of vents we identify are located within impact craters. The spatial distribution of vents does not correlate with the locations of volcanic smooth plains deposits, in contrast to the Moon, nor do vents correlate with the locations of large impact basins (except for the Caloris and Tolstoj basins). Using the degradation state of the vent host crater as a proxy for maximum age, we suggest that vent formation has been active through the Mansurian and into the Kuiperian periods, although the majority of vents were likely formed much earlier in mercurian history. The morphologies and locations of vents are used to investigate a set of plausible formation geometries. We find that the most likely and most prevalent formation geometry is that of a dike, stalled at depth, which then explosively vents to the surface. We compare the vent and deposit size of mercurian pyroclastic deposits with localized and regional lunar pyroclastic deposits, and find a range of possible eruption energies and corresponding variations in eruption style. Localized lunar pyroclastic deposits and the majority of mercurian pyroclastic deposits show evidence for eruption that is consistent with the magmatic foam at the top of a dike reaching a critical gas volume fraction. A subset of mercurian vents, including the prominent Copland-Rachmaninoff vent to the northeast of the Rachmaninoff basin, indicates eruption at enhanced gas volume fractions. This subset of vents shows a similar eruptive behavior to the lunar Orientale dark mantle ring deposit, suggesting that the dikes that formed these vents and deposits on Mercury underwent some form of additional volatile build-up either through crustal volatile incorporation or magma convection within the dike. There also exists a population of mercurian vents that no longer retain a visible associated pyroclastic deposit; we hypothesize that the visible signature of the pyroclastic deposit has been lost through space weathering and regolith mixing processes. Together, these results provide a comprehensive analysis of explosive volcanism on Mercury, and inform continued research on the thermal history of Mercury and magma composition and evolution.

Protein Adsorption and Reorganization on Nanoparticles Probed by the Coffee-Ring Effect: Application to Single Point Mutation Detection.

The coffee-ring effect denotes the accumulation of particles at the edge of an evaporating sessile drop pinned on a substrate. Because it can be detected by simple visual inspection, this ubiquitous phenomenon can be envisioned as a robust and cost-effective diagnostic tool. Toward this direction, here we systematically analyze the deposit morphology of drying drops containing polystyrene particles of different surface properties with various proteins (bovine serum albumin (BSA) and different forms of hemoglobin). We show that deposit patterns reveal information on both the adsorption of proteins onto particles and their reorganization following adsorption. By combining pattern analysis with adsorption isotherm and zeta potential measurements, we show that the suppression of the coffee-ring effect and the formation of a disk-shaped pattern is primarily associated with particle neutralization by protein adsorption. However, our findings also suggest that protein reorganization following adsorption can dramatically invert this tendency. Exposure of hydrophobic (respectively charged) residues can lead to disk (respectively ring) deposit morphologies independently of the global particle charge. Surface tension measurements and microscopic observations of the evaporating drops show that the determinant factor of the deposit morphology is the accumulation of particles at the liquid/gas interface during evaporation. This general behavior opens the possibility to probe protein adsorption and reorganization on particles by the analysis of the deposit patterns, the formation of a disk being the robust signature of particles rendered hydrophobic by protein adsorption. We show that this method is sensitive enough to detect a single point mutation in a protein, as demonstrated here by the distinct patterns formed by human native hemoglobin h-HbA and its mutant form h-HbS, which is responsible for sickle cell anemia.

Shallow-seated explosions in the construction of the Motukorea tuff ring (Auckland, New Zealand): Evidence from lithic and sedimentary characteristics

At least 52 eruption centres are scattered within the ~360km2 Auckland Volcanic Field (AVF). Motukorea, now an island in the Waitemata Harbour, is one of 39 AVF volcanoes that experienced a phreatomagmatic explosive phase, before a magmatic phase. The volcano erupted through a ~200–300m-thick, consolidated, mudstone/sandstone sequence of the Miocene Waitemata Group, which overlies the Waipapa Terrane greywacke basement. Detailed field descriptions of the sedimentary characteristics of the early phreatomagmatic deposits were carried out, along with examination of lithics. The ejecta ring deposit comprises 55 to 60vol.% lithics, of which Waitemata Group fragments constitute approximately 90vol.%, whereas <10vol.% are Waipapa fragments, suggesting a dominance of shallow fragmentation. The sedimentary characteristics of the stratigraphic sequence at Motukorea suggest a dominance of wet surges at the beginning of the eruption with progression into drier sequences upwards. This is reflected in increasing inter-bedded juvenile-pyroclast-dominated fall deposits up-sequence. These characteristics are attributed to the changing hydrogeological conditions within the diatreme and the host rocks. These findings shed light on the eruption dynamics of phreatomagmatic eruptions through consolidated rocks in the AVF and enable the depiction of a scenario of future eruptions within the field in similar substrates.

A theoretical individual-based model of Brown Ring Disease in Manila clams, Venerupis philippinarum

An individual-based mathematical model was developed to investigate the biological and environmental interactions that influence the prevalence and intensity of Brown Ring Disease (BRD), a disease, caused by the bacterial pathogen, Vibrio tapetis, in the Manila clam (Venerupis (=Tapes, =Ruditapes) philippinarum). V. tapetis acts as an external microparasite, adhering at the surface of the mantle edge and its secretion, the periostracal lamina, causing the symptomatic brown deposit. Brown Ring Disease is atypical in that it leaves a shell scar that provides a unique tool for diagnosis of either live or dead clams. The model was formulated using laboratory and field measurements of BRD development in Manila clams, physiological responses of the clam to the pathogen, and the physiology of V. tapetis, as well as theoretical understanding of bacterial disease progression in marine shellfish. The simulation results obtained for an individual Manila clam were expanded to cohorts and populations using a probability distribution that prescribed a range of variability for parameters in a three dimensional framework; assimilation rate, clam hemocyte activity rate (the number of bacteria ingested per hemocyte per day), and clam calcification rate (a measure of the ability to recover by covering over the symptomatic brown ring deposit), which sensitivity studies indicated to be processes important in determining BRD prevalence and intensity. This approach allows concurrent simulation of individuals with a variety of different physiological capabilities (phenotypes) and hence by implication differing genotypic composition. Different combinations of the three variables provide robust estimates for the fate of individuals with particular characteristics in a population that consists of mixtures of all possible combinations.The BRD model was implemented using environmental observations from sites in Brittany, France, where Manila clams routinely exhibit BRD signs. The simulated annual cycle of BRD prevalence and intensity agrees with observed disease cycles in cultured clam populations from this region, with maximum disease prevalence and intensity occurring from December to April. Sensitivity analyses of modeled physiological processes showed that the level of hemocyte activity is the primary intrinsic determinant of recovery of infected clams. Simulations designed to investigate environmental effects on BRD suggested that the outcome of the host–parasite interaction is dependent on food supply (high values being favorable for the host) and temperature. Results of simulations illustrate the complex interaction of temperature effects on propagation and viability of the bacterium, on the phagocytic activity of the hemocytes, and on other physiological processes of the host clam. Simulations using 1°C and 2°C increases in temperature generally favored disease development, indicating that climate warming might favor the spread of BRD.

Deposit pattern of inkjet printed pico-liter droplet

The deposit pattern of an evaporating picoliter droplet is studied changing the solvents (water, diethylene glycol, and formamide), mixing composition of the solvents and substrate temperature. When depinning occurs in the early stage of the evaporation period, concentrated solute (or partially deposited solute, if any) also retracts with the receding droplet, resulting in dome shaped deposit patterns. When pinning is maintained during most of the evaporation period, either a ring deposit or a relatively uniform deposit is obtained depending on the type of solvent and heating condition. These results are explained by interplay of (1) radial outward flow due to the strong evaporation flux at the contact line of a sessile droplet, (2) inward Marangoni flow due to evaporative cooling and solvent concentration gradient, and (3) solute mixing by diffusion in liquid.

Formation of Coffee Stains on Porous Surfaces

During the drying of drops of nanoparticle suspensions, segregation can occur by internal fluid flows toward the contact line, if the contact line is pinned. This leads to a characteristic ring deposit or coffee stain. On solid substrates coffee staining can be eliminated through the use of solvent mixtures that promote Marangoni flows to oppose these drying-induced flows. Here it is shown that a suspension, optimized to eliminate the formation of coffee stains on a range of solid surfaces, shows coffee staining on a number of porous surfaces. This behavior is shown to be consistent with a mechanism of fluid removal through capillary flow (draining) of the solvent into the porous substrate, combined with filtration of the particles by the small pore size, in addition to the flow from solvent evaporation. The extent of capillary driven coffee staining is a function of substrate pore size: if the pore size is small, capillary flow is slow, reducing the observed coffee staining. However, if the pore size is too large, the nanoparticles are absorbed into the material along with the draining solute and no deposition of particles is observed.

Pyranine-induced self-assembly of colloidal structures using poly(allylamine-hydrochloride)

Complexes of dyes and polyelectrolytes have found widespread use in a variety of functional materials and interfaces. Here it is found that upon mixing the anionic dye pyranine and a cationic polyelectrolyte, poly(allylamine-hydrochloride), two different colloidal structures may form. Above a certain concentration of anionic dye, crosslinking of the polyelectrolyte is initiated, and the formation of sheet-like colloidal structures was observed. Addition of hydroxyl ions resulted in the formation of micron-sized spherical colloids. It was also found that the colloidal shape transition was accompanied by a significant red-shift in the fluorescence emission. Combining fluorescence measurements with studies of the particle size with time, it was found that red-shift was related to the crosslinking of the dye and the polyelectrolyte, and was not influenced significantly by the aggregation and particle growth. Further information about the colloidal behavior and stability was obtained by letting droplets dry and follow the kinetics of this process. It was found that the particles collapsed near the contact line and formed a ring deposit, in agreement with previous studies. However, unlike previous studies, the thickness of the ring deposit did not grow significantly with time, due to the peculiar process of formation found here.

Radial-velocity profile along the surface of evaporating liquid droplets

The deposit pattern of drying liquid droplets has a close relationship with the radial-velocity profile along the droplet surface. In this paper, the surface temperature of the droplet is first solved numerically and approximated by a simple analytical form, and an analytical expression for the radial-velocity of the surface flow is then obtained by using the lubrication analysis developed by Hu and Larson. The theoretical analysis indicates that the outward surface flow will be reduced by the thermal Marangoni stress along the surface. When the Marangoni number is below a critical value, MaCrit, all the surface liquid will move outward and a dense, ring-like deposit will be formed. When above MaCrit, a stagnation point, within which the surface flow is inward and beyond which the surface flow is outward, will appear on the droplet surface. In such case, the particles transported to the surface beyond the stagnation point will move to the droplet edge to form the ring deposit, and the others will deposit on the central region of the droplet. Numerical results indicate that the critical Marangoni number decreases in a power law with the contact angle. The theory for the radial-velocity of the surface flow will be helpful to predict and control the deposit patterns from the drying droplets.

Intense Raman bands and low luminescence of thin films of heme proteins on silica

We use resonance Raman spectroscopy to study cytochrome c, hemoglobin and myoglobin from 50 μM solutions dried on a SiO 2 surface. Intense Raman spectra were observed with low luminescent background when excited at 488 nm with low laser power levels (0.6 mW) and relative short acquisition times (120 s). We estimate that 1 picogram of heme proteins can be detected. A polarization sensitive Raman band in cytochrome c near the edge of dried droplets suggests that the proteins line up in the ring deposit. This preferential orientation is suggested to contribute to the low luminescence back ground signal and to the larger Raman intensity compared to the heme proteins in powder form.

Microflow and Crack Formation Patterns in Drying Sessile Droplets of Liposomes Suspended in Trehalose Solutions

Anhydrobiotic preservation potentially provides a means of long-term storage of mammalian cells in carbohydrate glasses under ambient conditions. During desiccation, sessile droplets of glass-forming carbohydrate solutions exhibit complex phenomena, including fluid flow, droplet deformation, and crack formation, all of which may alter the cell preservation efficacy. Cell-sized liposomes were employed as a model system to explore these phenomena in diffusively dried sessile droplets of trehalose solutions. Two factors were identified that strongly influenced the features of the desiccated droplets: the underlying surface and the liposomes themselves. In particular, the surface altered the droplet shape as well as the microflow pattern and, in turn, the moisture conditions encountered by the liposomes during desiccation. A ring deposit formed when the droplets were dried on polystyrene, as would be expected owing to the capillary flow that generally occurs in pinned droplets. In contrast, when dried on the more hydrophilic glass slide, the resulting droplets were thinner, and the liposomes accumulated near their centers, which was an unexpected result likely owing to the glass-forming nature of trehalose solutions. As might be anticipated given the variations in liposome distribution, the choice of surface also influenced crack formation upon continued drying. In addition to providing a preferential path for drying, such cracks are relevant because they could inflict mechanical damage on cells. The liposomes themselves had an even more profound effect on crack formation; indeed, whereas cracks were found in all droplets containing liposomes, in their absence few of the droplets cracked at all, regardless of the surface type. These complex drying dynamics merit further investigation in the development of anhydrobiotic preservation protocols, particularly with regard to the role therein of surface hydrophobicity and the cells themselves.

Self-Organization of Carbon Nanotubes in Evaporating Droplets

Here, we report a simple and efficient way for organizing carbon nanotubes, in particular, single-wall carbon nanotubes (SWNTs) into ordered structures from their dilute solutions. It was found that drying a droplet of carbon nanotube solution at room temperature on a wettable surface such as glass or silica wafer led to redistribution, accumulation, and organization of carbon nanotubes along the perimeter of the droplet. Unlike the aggregation behaviors of colloid nanoparticles, anistropic carbon nanotubes tended to show two orientations in a ring deposit: one parallel to the outer perimeter of the ring and the other normal to it in the interior. Drying droplets of SWNT solutions at high temperatures exhibited a long-range ordered structure. In addition, droplet drying may cause size separation of carbon nanotubes and pattern formation through interactions between droplets. This result helps us not only to further understand fluid dynamics during the drying process but also to provide a promising and simple strategy for either assembling carbon nanotubes on a surface or organizing them into well-aligned films and fibers.

The Zamama–Thor region of Io: Insights from a synthesis of mapping, topography, and Galileo spacecraft data

We have studied data from the Galileo spacecraft's three remote sensing instruments (Solid-State Imager (SSI), Near-Infrared Mapping Spectrometer (NIMS), and Photopolarimeter-Radiometer (PPR)) covering the Zamama–Thor region of Io's antijovian hemisphere, and produced a geomorphological map of this region. This is the third of three regional maps we are producing from the Galileo spacecraft data. Our goal is to assess the variety of volcanic and tectonic materials and their interrelationships on Io using planetary mapping techniques, supplemented with all available Galileo remote sensing data. Based on the Galileo data analysis and our mapping, we have determined that the most recent geologic activity in the Zamama–Thor region has been dominated by two sites of large-scale volcanic surface changes. The Zamama Eruptive Center is a site of both explosive and effusive eruptions, which emanate from two relatively steep edifices (Zamama Tholi A and B) that appear to be built by both silicate and sulfur volcanism. A ∼100-km long flow field formed sometime after the 1979 Voyager flybys, which appears to be a site of promethean-style compound flows, flow-front SO 2 plumes, and adjacent sulfur flows. Larger, possibly stealthy, plumes have on at least one occasion during the Galileo mission tapped a source that probably includes S and/or Cl to produce a red pyroclastic deposit from the same vent from which silicate lavas were erupted. The Thor Eruptive Center, which may have been active prior to Voyager, became active again during the Galileo mission between May and August 2001. A pillanian-style eruption at Thor included the tallest plume observed to date on Io (at least 500 km high) and new dark lava flows. The plume produced a central dark pyroclastic deposit (probably silicate-rich) and an outlying white diffuse ring that is SO 2-rich. Mapping shows that several of the new dark lava flows around the plume vent have reoccupied sites of earlier flows. Unlike most of the other pillanian eruptions observed during the Galileo mission, the 2001 Thor eruption did not produce a large red ring deposit, indicating a relative lack of S and/or Cl gases interacting with the magma during that eruption. Between these two eruptive centers are two paterae, Thomagata and Reshef. Thomagata Patera is located on a large shield-like mesa and shows no signs of activity. In contrast, Reshef Patera is located on a large, irregular mesa that is apparently undergoing degradation through erosion (perhaps from SO 2-sapping or chemical decomposition of sulfur-rich material) from multiple secondary volcanic centers.