Peter J. Mouginis-Mark

Volcano/ground ice interactions in Elysium Planitia, Mars

Abstract The occurence within Elysium Planitia of meltwater deposits, possible pseudocraters, collapse features within troughs, and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area. The pseudocraters are interpreted to be indicators of near-surface volatiles, while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths. A latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35°N to greater than 600 m at 24°N, or that an ice wedge that existed at 35°N thinned to nonexistence at 24°N. Braided distributary channel systems within the chaotic terrain north of Elysium Planitia show that ephemeral lakes were repeatedly created and drained at this locality. The existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models. Morphological evidence for strombolian, vulcanian and plinian eruptions is lacking within western Elysium Planitia; there are no identifiable cinder cones, pyroclastic flow deposits, or mantled areas indicative of large airfall deposits at an image resolution of 50–150 m/pixel. However, the pseudocraters indicate that small-scale phreatomagmatic activity may have taken place.

Analysis of active lava flows on Kilauea volcano, Hawaii, using SIR-C radar correlation measurements

Precise eruption rates of active pahoehoe lava flows on Kilauea volcano, Hawaii, have been determined using spaceborne radar data acquired by the Space Shuttle Imaging Radar-C (SIR-C). A coastal site downslope from the Pu9u O9o vent was imaged once per day, on each of the four days of October 7–10, 1994. Day-to-day decorrelation due to resurfacing was determined by interferometric combination of the data at 15 m resolution over a wide area. On successive days, new lava resurfaced 335700 m 2 , 368775 m 2 , and 356625 m 2 . Assuming an average pahoehoe flow thickness of 50 cm, a mean effusion rate for this period is approximately 2 m 3 /s. The radar observations show persistent surface activity at each site, rather than downslope migration of coherent lava flows.

Radiative temperature measurements at Kupaianaha lava lake, Kilauea Volcano, Hawaii

Field spectroradiometer data in the wavelength range of 0.4–2.5 μm and spectral resolution of 1–5 nm have been used to compute the radiative temperature of the surface of Kupaianaha lava lake, Kilauea Volcano, Hawaii. Two sets of observations (a total of 120 spectra) were made on October 12, 1987, and January 23, 1988, when the lava lake was in a period of active overturning. The area of the surface for which temperatures were measured was ∼0.23–0.55 m2. Two numerical models of two and three components have been used to match the measured radiant flux ratios and to describe the surface of the lava pond in terms of radiant area and temperature. Three stages of activity on the lake surface are identified: Stage 1, characterized by magma fountaining and overturning events exhibited the hottest crustal temperatures (180–572°C) and the largest fractional hot areas (> 10−3). Stage 1 average flux densities were ∼2.2 × 104 W/m2, the highest recorded for the three stages of activity on either day. The largest radiative area of fresh magma was 29% at 1100°C, while cooling from magmatic temperatures to newly formed crust at 790°C took place in a matter of seconds. Stage 2, marked by rifting events between plates of crust, exhibited crustal temperatures between 100 and 340°C with fractional hot areas at least an order of magnitude lower than those found for stage 1. Average flux densities calculated for three examples of stage 2 activity were 5.3 × 103 W/m2. Stage 3, which was quiescent periods when the lake was covered by a thick crust, dominated the activity of the lake both temporally and spatially over 90% of the time. The characteristic crustal temperature of stage 3 was 80–345°C with most solutions near 200–300°C and fractional hot areas of ≤ 10−5 of the viewing area. Average flux densities for stage 3 were 4.9 × 103 W/m2. For many stage 3 examples, a two-component model was sufficient to describe the spectral data; however, for almost all of the stage 1 and 2 examples and the remainder of the stage 3 examples a three-component model was required. These determinations of lava temperature and radiant area have relevance for satellite and airborne measurements of the thermal characteristics of active volcanoes and indicate that temporal variability of the thermal output of lava lakes occurs on the time scale of seconds to minutes.

Ejecta emplacement and modes of formation of martian fluidized ejecta craters

Abstract From an analysis of 1173 craters possessing single (Type I) and double (Type 2) concentric ejecta deposits, Type 2 craters are found to occur most frequently in areas that have also been described as possessing periglacial features. The frequency of occurence of central peaks and wall failure (terraces plus scallops) within the craters indicate that, by analogy with previous analyses, Type 1 craters form in more fragmental targets than Type 2 craters. The maximum range of the outer ejecta deposits of Type 2 craters, however, consistently extends ∼0.8 crater radii further than ejecta deposits of Type 1 craters, suggesting a greater degree of ejecta fluidization for the twin-lobed Type 2 craters. Numerous characteristics of Ries Crater, West Germany, show similarities to craters on Mars, indicating that Martian fluidized ejecta craters may be closer analogs to this terrestrial crater than are lunar craters.

Recent water release in the Tharsis region of Mars

Abstract Numerous channels have been identified in northwestern Tharsis, Mars, at the base of the Olympus Mons escarpment and to the west of Ceraunius Fossae. These channels are anastomosing in form, and have associated streamlined islands, indicating they were most likely formed by flowing water. The preferred model for channel formation involves either the tectonic release of water from a deep groundwater system or, less likely, the intrusive heating of deep-seated ice lenses. Because the channels are carved in some of the youngest lava flows on Mars, it is believed that water or ice existed at certain places at equatorial latitudes until the recent

Elysium planitia, mars: Regional geology, volcanology, and evidence for volcano-ground ice interactions

Geological mapping of Elysium Planitia has led to the recognition of five major surface units, in addition to the three volcanic constructs Elysium Mons, Hecates Tholus, and Albor Tholus. These units are interpreted to be both volcanic and sedimentary or erosional in origin. The volcano Elysium Mons is seen to have dominated constructional activity within the whole region, erupting lava flows which extend up to 600km from the summit. A major vent system, covering an area in excess of 75 000 km2, is identified within the Elysium Fossae area. Forty-one sinuous channels are visible within Elysium Planitia; these channels are thought to be analogous to lunar sinuous rilles and their formation in this region of Mars is attributed to unusually high regional topographic slopes (up to ~ 1.7‡). Numerous circumferential graben are centered upon Elysium Mons. These graben, located at radial distances of 175, 205–225, and 330km from the summit, evidently post-dated the emplacement of the Elysium Mons lava flows but pre-dated the eruption of extensive flood lavas to the west of the volcano. A great diversity of channel types is observed within Elysium Fossae. The occurrences of streamlined islands and multiple floor-levels within some channels suggests a fluvial origin. Conversely, the sinuosity and enlarged source craters of other channels suggests a volcanic origin. Impact crater morphology, the occurrence of chaotic terrain, probable pyroclastic deposits upon Hecates Tholus and fluvial channels all suggest extensive volcano-ground ice interactions within this area.

Water or ice in the Martian regolith? - Clues from rampart craters seen at very high resolution

Abstract Very high resolution Viking Orbiter images (8–17 m per pixel) have been used to investigate the morphology of Martian rampart crater ejecta blankets and the crater interiors, with the objective of identifying the fluidizing medium for the ejecta and the physical properties of the target rock. The occurrence of well-preserved, small-scale pressure ridges and scour marks, evidence for subsidence around isolated buried blocks in partially eroded ejecta lobes, and the stability of crater walls and distal ramparts argue for ground ice being the dominant state for volatiles within the target rocks at the time of impact. Rare examples of channels (190–650 m wide) on the surfaces of ejecta blankets, and on the inner walls of the crater Cerulli, indicate that in some instances liquid water was incorporated into the ejecta during its emplacement. No morphological evidence has been found to discount the idea that atmospheric effects were partially responsible for ejecta fluidization, but it is clear that these effects were not the sole reason for the characteristic lobate deposits surrounding at least some rampart craters on Mars.

Polygenic eruptions on Alba Patera, Mars

A combination of photogeologic mapping, analysis of Viking Orbiter thermal inertia data, and numerical modelling of eruption conditions has permitted us to construct a new model for the evolution of the martian volcano Alba Patera. Numerous digitate channel networks on the flanks of the volcano are interpreted to be carved by sapping due to the release of non-juvenile water from unconsolidated flank deposits. Using the thermal inertia measurements, we estimate the particle size of these deposits to be 3–10 µm, which, together with theoretical modelling of the disperison of explosively derived volcanic materials, leads us to conclude that the flank deposits on Alba Patera are low-relief pyroclastic flows. The recognition of numerous late-stage summit and sub-terminal lava flows thus makes Alba Patera a unique martian volcano that is transitional between the older pyroclastic-dominated highland paterae and the more recent effusive central-vent volcanoes such as the Tharsis Montes.

Geologic analyses of Shuttle Imaging Radar (SIR-B) data of Kilauea Volcano, Hawaii

Analyses of imaging radar data of volcanic terranes on Earth and Venus have emphasized the need for a clearer understanding of how these data can be most effectively used to accomplish important volcanological goals, including the interpretation of eruptive styles and the characterization of the geologic history of volcanic centers. The second Shuttle Imaging Radar experiment (SIR-B) obtained two digital images over the summit caldera and the Southwest Rift Zone of Kilauea Volcano in 1984. Our geologic analyses of these images indicate that SIR-B data are particularly useful for delineating the distribution and surface textural variations of a9a lava flows, for mapping large-scale topographic features with radar-facing slopes, and for identifying an areally extensive pyroclastic deposit. Analyses of the SIR-B data of Kilauea, however, do not permit unambiguous identification of landforms such as pahoehoe lava flows, cinder cones, and fissures. Although separation of low-return units such as pahoehoe lava flows and adjacent pyroclastic ash is not greatly improved using standard image-enhancement techniques, the texture-analysis technique applied here did facilitate discrimination of such smooth-surfaced volcanic deposits. Although analyses of the SIR-B data permit a generally accurate interpretation of the eruptive history of Kilauea, the inability to distinguish low-return pahoehoe flows results in misinterpretation of several aspects of Kilauea volcanism, suggesting that caution should be exercised in the interpretation of SAR data of volcanic terranes.

Analysis of active volcanoes from the earth observing system

Abstract A study of volcanic activity and its effects on the atmosphere is one of 28 interdisciplinary investigations, for the Earth Observing System (EOS), due to be launched in 1997 and 1999. The volcanology investigation will include long- and short-term monitoring of selected volcanoes, the detection of precursory activity associated with unanticipated eruptions, and the detailed study of on-going eruptions. The data collected will allow us to address two aspects of volcanism: volcanic padforms and the atmospheric effects of eruptions. A variety of instruments on the two NASA EOS platforms, together with supplemental data from the Japanese and European platforms, will enable the study of local- to regional-scale thermal and deformational features of volcanoes, and the chemical and structural features of volcanic eruption plumes and aerosols. This investigation fits well within the overall goal of the EOS Project, which is to study the regional and global interrelationships between components of the Earth System, because it specifically investigates the links between volcanism, atmospheric chemistry and short-term (1–3 year) climate change.