Engineering topics
Theilig, E.
Publications and source records attributed to Theilig, E..
Project Galileo Completing Europa, Preparing for Io
Galileo has completed the Europa leg of the Galileo Europa Mission, and is now pumping down the apojove in each succeeding orbit in preparation for the Io phase.
Radar interpretation of lava fields as a function of incidence angle - Implications for interpretation of Magellan SAR data on Venus
The capability of a single frequency, single polarization radar to distinguish different lava flows solely on the basis of their relative radar backscatter as measured by scatterometer profiles is addressed. It is found that mantled and unmantled flow surfaces can be separated by their radar backscatter and become more distinct with increasing incidence angle. Pristine pahoehoe surfaces have backscatter coefficients distinctly different from older flows at small angles, whereas the most modified pahoehoe units are identifiable at larger incidence angles. At all latitudes on Venus, it should be possible to distinguish the style of volcanism responsible for volcanic plains emplacement.
Small-scale volcanic landforms indicative of distributary tube systems
Surface features tens to hundreds of meters in size on Martian lava flows are revealed in high resolution Viking Orbiter images. Many of these morphological features form in response to certain flow emplacement mechanisms, eruptive styles, or rheological properties of the lava. Insight into the relationships between lava flow morphology and the emplacement and characteristics of magma is an ongoing areas of research and allows constraints to be placed on interpretation of Martian volcanism. This report focuses on pressure ridges, tumuli, and pressure plateaus which comprise a suite fo features characteristics of compound pahoehoe lava flows. Similar ridges and mounds were identified in the Tharsis region of Mars.
Martian volcanism: Festoon-like ridges on terrestrial basalt flows and implications for Mars
The Fink and Fletcher, and Fink model was used to assess and compare flow rheology for two terrestrial basalt flows and one Martian flow with previous studies. Based on the morphologic similarities between the Martian flows and the Icelandic flows and knowledge of the emplacement of the terrestrial flows, the flows west of Arsia Mons are considered to have been emplaced as large sheet flows from basaltic flood style eruptions. Festoon ridges represent folding of the surface crust in the last stages of emplacement when viscosities would be high due to cooling. Alternatively, the lava may have had a high crystallinity or was erupted at low temperatures. In addition, increased compressive stress behind halted flow fronts or in ponded areas may have contributed to ridge formation.
Lava flows on Mars - Analysis of small surface features and comparisons with terrestrial analogs
High-resolution images of south and west Arsia Mons, eastern Tharsis, and Memnonia Fossae on Mars are analyzed. Lava flows with different types of features, such as pressure ridges, tumuli, festoon ridges, and ring ridges, are observed. The effects of these small features on the type of eruption, mode of flow emplacement, and characteristics of the terrain over which the lavas flow are examined. The development of terrestrial pressure ridges, festoon, and ring structures is discussed and they are compared to the observed Martian features. The interior viscosity of the features are calculated using the Fink and Fletcher (1978) and Fink (1980a) models; the interior viscosity was estimated as 100 MPa sec in flow margins, ponded areas, and across flow lobes. The data reveal that south of Arsia Mons, flows containing pressure ridges are emplaced as multiple flow units from sporadic low-effusion rate eruptions, and the flows at the other three areas are large sheet flows that represent basaltic flood-type volcanism.
Basaltic Pressure Ridges: Formation and Relationship to Flow Emplacement
Pressure ridges and pressure plateau are common but not ubiquitous surface features on terrestrial basaltic lava flows and may reflect a specific flow emplacement mechanism. Many of the ridges are large enough to be detected on high-resolution orbital images; therefore, understanding these features could provide a means for interpreting volcanic flows on the mechanism of pressure ridge formation and how their formation relates to flow emplacement. Results from detailed field studies indicate that pressure ridges and plateaus: (1) are emplaced as individual flow lobes, (2) can be composed of primary or secondary material, (3) are dependent on duration and volume of activity within the flow unit, (4) are penecontemporaneous in formation, and (5) are indicative of slowly advancing flows with numerous flow lobes continuously forming and overriding each other.
The Mauna Loa sulfur flow as an analog to secondary sulfur flows on Io
Independent evidence suggests that both sulfur and silicate materials exist on the surface of Io. Spectral data indicate the presence of sulfur compounds, some of which are suggested to be of fumarolic origin. Morphological evidence and inferences of the physical properties of some land-forms suggest that silicate volcanism has occurred, which would involve temperatures 650 C or greater. Because the liquidus of sulfur is only about 115 C, it is likely that sulfur in close proximity to 'hot spots' or to active silicate volcanic areas on Io would be melted and mobilized as flows. The Mauna Loa sulfur flow may serve as an analog for such flows, as it consists of fumarolic sulfur that was melted as a consequence of a basaltic eruption and produced a small flow superimposed on silicate lavas.
The 1950 sulfur flow of Mauna Loa: Considerations for Io
Some of the geological relationships observed in the Mauna Loa sulfur flow may apply in considering volcanic processes on Io. Given the presence of sulfur/sulfur compounds in the eruption plumes and on the surface of Io, it is likely that extensive secondary deposits of sulfur exist, some of which may be of fumarolic origin and analogous to the Mauna Loa deposit. Given the likelihood of silicate volcanism of Io based on the inferred material properties of some flows, and the attendant high temperatures for silicate volcanism, it is likely that the secondary surface deposits of sulfur would have been mobilized without being heated to the high viscosity stage. Mobilized sulfur flows on Io may flow long distances as a result of: (1) low viscosities in the melting range; (2) sustained effusion resulting from continued heating source area; (3) continued remobilization within the flow as a consequence of surges from the source; and (4) extension via lava tubes, or similar conduits through which there is little heat loss. Sulfur flows may form a relatively thin veneer over silicate flows and other surface units, given their fluidity and low mobilization temperature. Active splashing and splattering may spread sulfur over a wider area contributing the bright blooms observed in association with some Ionian flows.
Ridges on basalt flows
Pressure ridges are surface features on basaltic lava flows and, as with other surface features, they may be related to the emplacement of a flow and the rheological properties of the lava. Since many ridges are of sufficient size to be detected on high resolution orbital images, an understanding of pressure ridges could provide a means for interpreting volcanic flows on other terrestrial planets. Some proposed formation mechanisms are reviewed and three different types of pressure ridges are identified on the basis of morphology. Type 1 ridges are the most common and are associated with multiple flow unit pahoehoe in which the ridges are embayed by secondary toe fed lava. They tend to be restricted to wider sections or margins of the flow and to be oriented longitudinal to flow direction; however, oblique or transverse orientation is not uncommon. Bulbous squeeze ups are common within cracks and may reflect relative timing of crack formation. The interior structure of type 1 ridges consists of an upper slab section which generally contains columnar joints and a lower massive section with an irregular surface. This basic distinction may mark the thickness of the surface crust when ridge formation was initiated. Type 2 ridges occur in association with type 1 and are very similar with the exception of the secondary squeeze out material. Instead of only filling cracks, the secondary material on these ridges originated from underneath a thin crust and flowed as toes or channels from the top and sides of the ridge. Type 3 ridges have much steeper sides (almost vertical at the top) than the other types. Medial cracks are very wide and the crack walls are convex upward. No squeeze ups are present. The main difference between type 3 and the others may be reflection of viscosity.
A primer on sulfur for the planetary geologist
Sulfur has been proposed as the dominant composition for the volcanic material on Io. Sulfur is a complex element which forms many intramolecular and intermolecular allotropes exhibiting a variety of physical properties. Cyclo-S8 sulfur is the most abundant and stable molecular form. The important molecular species within liquid sulfur change in concentration with temperature. Concentrations of the allotropes control the physical properties of the melt. Discontinuities in density, viscosity, and thermal properties reflect the polymerization process within liquid sulfur. Variations in the melting point are related to autodissociation of the liquid. Many solids forms of sulfur have been identified but only orthorhombic alpha and monoclinic beta sulfur, both composed of cyclo-S8 sulfur, are stable under terrestrial conditions. Physical properties of solid sulfur are dependent on the allotrope and, in some cases, the thermal history. Three natural terrestrial sulfur flows are described: (1) Siretoko-Iosan, Japan; (2) Volcan Azufre, Galapagos Islands; and (3) Mauna Loa, Hawaii. All of the flows are associated with fumarolic areas and are considered to have formed by the melting and mobilization of sulfur deposits. Surface textures of the flows indicate a behavior of molten sulfur similar to that of silicate lava. Channels, rivulets, and lobate edges were described for the flows. The solidification of man-made sulfur flows formed as part of the Frasch mining process by which sulfur is removed from the subsurface in a liquid state is described.
Plains and channels in the Lunae Planum-Chryse Planitia region of Mars
The Lunae Planum-Chryse Planitia region provides the opportunity to study a sequence of channeling events and to determine their temporal and genetic relationships to plains units in the northern hemisphere of Mars. Two sets of small channels and four major channel systems can be divided into four periods of channeling by superposition and contact relationships to the plains. All of the channels are considered to have formed by water erosion. The first two channeling events occurred early in the history of this area and formed small, narrow channels within the old rugged terrain. These channel events were separated by deposition of a mantle unit. The small channels probably formed by runoff of surface water or by a sapping process. These channels preceded the emplacement of vast volcanic plains in both Lunae Planum and Chryse Planitia. Channels postdating the plains are Vedra, Maumee, Bahram, and Maja valles; the first three of these deposited a sedimentary unit on the western slope of Chryse Planitia that was eroded by Maja Vallis. These large-scale channels were probably formed predominantly by catastrophic floods and may represent two periods of water release from Juventae Chasma. The origin of Bahram Vallis remains uncertain.
Geology of Chryse Planitia
Chryse Planitia, the site of the first successful landing on Mars by Viking 1, is an asymmetrical basin, centered at 45 deg W and 24 deg N, about 2000 km northeast of Valles Marineris. High-resolution Viking orbiter images show Chryse Planitia to be much more complex than had been suspected from Mariner 9 images. On the basis of a study of the Viking pictures it is concluded that the geological history of Chryse Planitia involves a complex sequence of impact cratering, mantling by extensive deposits of unknown origin, redistribution of mantling and crater materials by erosion and deposition with concurrent eruptions of flood-type basalts, and aeolian activity.