David C. Pieri

COASTAL GEOMORPHOLOGY OF THE MARTIAN NORTHERN PLAINS

The paper considers the question of the formation of the outflow channels and valley networks discovered on the Martian northern plains during the Mariner 9 mission. Parker and Saunders (1987) and Parker et al. (1987, 1989) data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains. It is suggested, that of the geological processes capable of producing similar morphologies on earth, lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on Mars.

Eruption rate, area, and length relationships for some Hawaiian lava flows

Abstract Volcanic geomorphologists have investigated various relationships between eruption rate and morphologic parameters of lava flows, particularly with regard to preferred statistical correlations and the conditions under which they are valid. Here we employ two simple models for lava flow heat loss by Stefan-Boltzmann radiation to derive eruption rate versus planimetric area relationships. Both of these models predict a linear relationship between eruption rate and planimetric area, modulated by distinct prefactors potentially sensitive to compositional and temperature differences among different flows. Regardless of any theoretical considerations, we show that eruption rate is highly correlated with planimetric area for the Hawaiian basaltic flows analyzed in this work. Moreover, this observed correlation is superior to those from other obvious combinations of eruption rate and flow dimensions. On the basis of the theoretical models for lava flow heat loss, the correlations obtained here suggest that the surfaces of Hawaiian flows radiate at an effective temperature much less than the inner parts of the flowing lava in agreement with numerous field observations. This work also indicates that eruption rate versus planimetric area correlations can be markedly degraded when data from different vents, volcanoes and epochs are combined. These previously unrecognized sensitivities identified by the thermal loss modeling may have contributed to past unresolved debates on relationships between eruption rates and morphologic dimensions.

Thermal radiance observations of an active lava flow during the June 1984 eruption of Mount Etna

The thermal budget of an active lava flow observed on 20 June 1984 from the Southeast crater of Mount Etna, Sicily, Italy, was analyzed from data taken by the Landsat Thematic Mapper. The Thematic Mapper images constitute one of the few satellite data sets of sufficient spatial and spectral resolution to allow calibrated measurements on the distribution and intensity of thermal radiation from active lava flows. Using radiance data from two reflective infrared channels, we can estimate the temperature and areas of the hottest parts of the active flow, which correspond to hot (>500 °C) fractures or zones at the flow surface. Using this technique, we estimate that only 10%-20% of the total radiated thermal power output is emitted by hot zones or fractures, which constitute less than 1% of the observed surface area. Generally, it seems that only where hot fractures or zones constitute greater than about 1% of the surface area of the flow will losses from such features significantly reduce internal flow temperatures. Using our radiance observations as boundary conditions for a multicomponent thermal model of flow interior temperature, we infer that, for the parts of this flow subject to analysis, the boundary layer and flow thickness effects dominate over radiant zones in controlling the depression of core temperature.

Crystallization History of the 1984 Mauna Loa Lava Flow

During a 3-week eruption in 1984, Mauna Loa produced vent lavas that increased in crystallinity from <1 to 30%, and 27-km-long flows that increased in crystallinity as they moved downstream. We examined the crystallization history of these lavas using crystal size distribution (CSD) analysis to study the rates of crystallization, viscosity increase, and latent heating. Typical average growth and nucleation rates were 5×10−9 cm s−1 and 5 cm−3 s−1 for microphenocrysts (20- to 500-μm size crystals nucleated in the rift zone) and 5×10−8 cm s−1 and 5 × 104 cm−3 s−1 for microlites (1- to 20-μm size crystals nucleated in the channel). These crystallization rates are high compared with those found in other CSD studies of igneous rocks, probably due to highly nonequilibrium conditions brought on by rapid degassing in the rift zone and cooling in the lava channel. Growth and nucleation rates decreased with time at the vent and with distance downstream. The maximum downstream total crystallinity measured is 39% (25% microlites, 14% microphenocrysts) in a quenched sample 14 km from the vent. Growth and nucleation rates cannot be calculated for postemplacement samples, but they place upper limits of 53–58% on the amount of crystallization in the channel 9–20 km from the vent. Crystallization could have been mostly responsible for the 105-fold downstream increase in apparent viscosity, although degassing and increasing incorporation of solid lava fragments also contributed. Another effect of crystallization on the lava flow was the sizeable latent heating (0.01 J g−1 s−1 over the first half of the flow length, if the crystallinity of downstream quench samples is representative of the hot fluid core), which may have been counteracted by entrainment of cooler material. Measurements of crystallization are shown to be crucial in the study of lava flow emplacement dynamics.

Failures in Detecting Volcanic Ash from a Satellite-Based Technique

Abstract Immediate and accurate detection of airborne volcanic ash is an operational imperative of the aviation industry, especially jet aircraft. Ash encounters place passengers aboard these aircraft at severe risk and significantly impact, via forced rerouting, both the safety and profit margins of freight carriers due to their limited fuel supply. Moreover, the airlines can suffer high economic costs for repair and replacement of equipment. Operational detection and tracking of volcanic ash by most national weather services has relied heavily on a split window differencing technique of thermal longwave infrared channels on currently operational satellites. Unfortunately, prior work on volcanic ash detection has not emphasized the dynamical interaction between the erupting volcano and the effects of overlying atmospheric water vapor, phreatic and phreatomagmatic water sources. Six volcanic ash eruptions from around the globe were chosen for study because they have wide variation in ambient atmospheric water vapor, available ground and surface water and different magma types. Results show that the present differencing technique is not uniformly effective in properly classifying volcanic ash pixels in the satellite scene and often falsely interprets meteorological clouds as volcanic ash clouds and conversely. Moreover, it is not always a robust early detector, an operational aviation requirement. Seasonal variability in global integrated atmospheric water vapor, coupled with the geographical distribution of currently active volcanoes, suggests the concerns discussed herein with regard to six specific eruptions, have applicability to the global aviation industry. Operational implications are discussed and a strategic proposal is presented on necessary steps to improve detection.

Emplacement of the 75-km-long Carrizozo lava flow field, south-central New Mexico

Abstract The Carrizozo Lava flow field is a young, 75-km-long, compound tube-fed pahoehoe flow field located in south-central New Mexico. Topographic channeling, unusually low viscosity, and fissure vents are ruled out as possible explanations for the length of the flow field. Effusion rates are estimated using: (1) a Bingham plastic model; (2) correlations between flow morphology and effusion rate; and (3) comparison with Hawaiian pahoehoe flows. The Bingham plastic model placed no useful restrictions on the effusion rate, while empirical and theoretical correlations gave estimates between 300 and 3 × 10 5 m 3 s −1 for the effusion rate. The striking morphological similarity of the Carrizozo flow field to the compound tube-fed pahoehoe Kupaianaha flow field on Kilauea Volcano suggests an effusion rate of about 5 m 3 s −1 and an eruption duration of nearly 3 decades. This long eruption duration and a long-lived lava tube system are interpreted to be the most important factors responsible for the length of the Carrizozo flow field. Furthermore, we conclude that the Bingham plastic model does not apply to tube-fed pahoehoe flow fields and that the correlation techniques grossly overestimate their effusion rates. This indicates that effusion rates may also have been overestimated for extra-terrestrial lava flows where it is has not been possible to distinguish between pahoehoe and ‘a’a.

Multispectral thermal infrared mapping of the 1 October 1988 Kupaianaha flow field, Kilauea volcano, Hawaii

Multispectral thermal infrared radiance measurements of the Kupaianaha flow field were acquired with the NASA airborne Thermal Infrared Multispectral Scanner (TIMS) on the morning of 1 October 1988. The TIMS data were used to map both the temperature and emissivity of the surface of the flow field. The temperature map depicted the underground storage and transport of lava. The presence of molten lava in a tube or tumulus resulted in surface temperatures that were at least 10° C above ambient. The temperature map also clearly defined the boundaries of hydrothermal plumes which resulted from the entry of lava into the ocean. The emissivity map revealed the boundaries between individual flow units within the Kupaianaha field. In general, the emissivity of the flows varied systematically with age but the relationship between age and emissivity was not unique. Distinct spectral anomalies, indicative of silica-rich surface materials, were mapped near fumaroles and ocean entry sites. This apparent enrichment in silica may have resulted from an acid-induced leaching of cations from the surfaces of glassy flows. Such incipient alteration may have been the cause for virtually all of the emissivity variations observed on the flow field, the spectral anomalies representing areas where the acid attack was most intense.

Sulfur flows of Ra Patera, Io

Abstract Voyager 1 imaging data have been used to investigate the color and morphology of several radial flow-like features at Ra Patera, a broad volcanic structure at approximately 8° latitude and 325° longitude on the Galilean satellite Io (J1). It was found that downstream progressions of flow color and morphology are consistent with lava of a predominately sulfur composition cooling radiatively and erupting in the range of 470 to 520°K at effusion rates at 1010 to 1011 cm3/sec. This implies global resurfacing rates by volcanic flows on Io of the order of 1 cm/year. Calculated energy content and effusion rates for flows at Ra Patera, using the physical parameters of sulfur, are of the order of the largest known terrestial basaltic eruptions and are consistent with calculations of globally available energy.

The February 2001 Eruption of Mount Cleveland, Alaska: Case Study of an Aviation Hazard

Mount Cleveland, Alaska (528499N, 1698579W), located on Chuginadak Island, erupted on 19 February 2001. The atmosphere‐volcanic plume interactions that occurred as part of this event led to several serious encounters of commercial aircraft with the ash. A number of continental and oceanic air traffic control areas were affected. Here, a detailed case study of the eruption, subsequent movement of the airborne plume, and operational response is presented. The likelihood of such encounters in the future may be reduced as a result of lessons learned from this event. Some potential new assets for improving the detection of and response to the airborne volcanic ash hazard to aviation also are discussed.

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.