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NASA NTRS1992

Recent Elysium volcanism: Effects on the Martian atmosphere

A vast area of smooth plains in southeastern Elysium near 5 deg N, 195 deg was identified as young volcanic plains. These plains represent flood eruptions of very low viscosity lavas at a point in time much later than the volcanism that produced the major volcanoes of Elysium. Since volcanism is a principal mechanism by which gases are supplied to the atmosphere, and since these gases can have important climatic effects, it is important to consider the amount of H2O, CO2, and other gases that were possibly released. We present estimates of input and release rates from this volcanic episode. The age is defined by the density of superposed craters; there are 89 +/- 15 craters greater than or equal to 1 km per 10(exp 6) sq km corresponding to the Upper Amazonian making this the youngest major volcanic episode. Lavas, covering 1.5 x 10(exp 6) sq km and presumably erupted through fissures, filled a topographic low and then flowed through knobby terrain into westernmost Amazonis. The western plains are characterized by scattered low shields having radial lava flows. Unit thickness is uncertain, individual flows are about 10 m thick; the entire deposit buries older knobby terrain having local relief of 200-400 m (estimated by Earth-based radar data); hence the volcanics must be thick enough to bury that relief. On the basis of unit morphology, length of flows, and the extent of the deposit, it can be inferred that the lava was of low viscosity and mafic to ultramafic composition. The age and petrology of the shergottites suggest they may have come from this unit.

Plescia, J. B.↗
NASA NTRS1992

Chemical reaction path modeling of hydrothermal processes on Mars: Preliminary results

Hydrothermal processes are thought to have had significant roles in the development of surficial mineralogies and morphological features on Mars. For example, a significant proportion of the Martian soil could consist of the erosional products of hydrothermally altered impact melt sheets. In this model, impact-driven, vapor-dominated hydrothermal systems hydrothermally altered the surrounding rocks and transported volatiles such as S and Cl to the surface. Further support for impact-driven hydrothermal alteration on Mars was provided by studies of the Ries crater, Germany, where suevite deposits were extensively altered to montmorillonite clays by inferred low-temperature (100-130 C) hydrothermal fluids. It was also suggested that surface outflow from both impact-driven and volcano-driven hydrothermal systems could generate the valley networks, thereby eliminating the need for an early warm wet climate. We use computer-driven chemical reaction path calculation to model chemical processes which were likely associated with postulated Martian hydrothermal systems.

Plumlee, Geoffrey S.↗
NASA NTRS1992

Raman Lidar Measurements of Pinatubo Aerosols over Southeastern Kansas During November-december 1991

The eruptions of the Philippine volcano Pinatubo during June 1991 produced large amounts of stratospheric aerosols that could significantly affect earth's climate as well as trigger stratospheric ozone depletion through heterogeneous chemical reactions. Information regarding the physical and optical properties of these aerosols is required to quantify those effects. By measuring both the elastically backscattered signal and the inelastic signal produced by Raman scattering from nitrogen molecules, Raman lidar can provide some of this information. In this presentation we discuss Raman lidar measurements of the scattering ratio, backscattering, extinction, extinction/backscattering ratio, and optical thickness of the Pinatubo aerosols over southeastern Kansas made on 10 nights during November and December, 1991. The Raman lidar developed at GSFC is a trailer-based system which uses an XeF excimer laser to transmit light at 351 nm. The light backscattered by molecules and aerosols at this wavelength is detected as well as Raman scattered light from water vapor, nitrogen, and oxygen molecules. Since background skylights interfere with the detection of the Raman signals the data discussed in this paper were acquired only at night.

Ferrare, R. A.↗
NASA NTRS1992

Lidar Observations of Stratospheric Aerosol Layer After the Mt. Pinatubo Volcanic Eruption

The volcano Mt. Pinatubo located on the Luzon Island, Philippines, had explosively erupted on June 15, 1991. The volcanic eruptions such as volcanic ash, SO2 and H2O reached into the stratosphere over 30 km altitude by the NOAA-11 satellite observation and this is considered one of the biggest volcanic eruptions in this century. A grandiose volcanic eruption influences the atmosphere seriously and causes many climatic effects globally. There had been many impacts on radiation, atmospheric temperature and stratospheric ozone after some past volcanic eruptions. The main cause of volcanic influence depends on stratospheric aerosol, that stay long enough to change climate and other meteorological conditions. Therefore it is very important to watch stratospheric aerosol layers carefully and continuously. Standing on this respect, we do not only continue stratospheric aerosol observation at Tsukuba but also have urgently developed another lidar observational point at Naha in Okinawa Island. This observational station could be thought valuable since there is no lidar observational station in this latitudinal zone and it is much nearer to Mt. Pinatubo. Especially, there is advantage to link up these two stations on studying the transportation mechanism in the stratosphere. In this paper, we present the results of lidar observations at Tsukuba and Naha by lidar systems with Nd:YAG laser.

Nagai, Tomohiro↗
NASA NTRS1992

A New Raman DIAL Technique for Measuring Stratospheric Ozone in the Presence of Volcanic Aerosols

This paper describes a new lidar scheme to measure stratospheric ozone in the presence of heavy volcanic aerosol loading. The eruptions of the Philippine volcano Pinatubo during June 1991 ejected large amounts of sulfur dioxide into the atmosphere to altitudes of at least 30 km. The resulting aerosols have severely affected the measurements of stratospheric ozone when using traditional Rayleigh differential absorption lidar (DIAL) technique, in which the scattering mechanism is almost entirely Rayleigh and which assumes a small amount or no aerosols. In order to extract an ozone profile in the regions below about 30 km where the Rayleigh lidar returns are contaminated by aerosol scattering from Mt. Pinatubo cloud, we have used a Raman lidar technique, where the scattering mechanism depends solely on molecular nitrogen. In this scheme there is no aerosol scattering component to the backscattered lidar return. Using this technique in conjunction with the Rayleigh DIAL measurement, the GSFC stratospheric ozone lidar has measured ozone profiles between 15 and 50 km during the recently held UARS correlative measurement campaign (February-March 1992) at JPL's Table Mountain Facility in California.

Upendra N. Singh↗
NASA NTRS1992

Observations of Ozone-aerosol Correlated Behaviour in the Lower Stratosphere During the EASOE Campaign

The question of possible interactions between ozone and stratospheric aerosol has been open for a long time. Measurements carried out after the Mt. Agung and El Chicon eruptions showed evidence of negative correlations between the presence of volcanic stratospheric aerosols and ozone concentration. Evidence for negative correlations in the polar winter has been also found. It is only after the discovery of the Antarctic ozone hole that catalytic effects related to low temperature heterogeneous chemistry have become the object of much investigation, now extended to the role of volcanic aerosol in the ozone reduction. These phenomena can be the object of various interpretations, not mutually exclusive, including the effect of transport, diffuse radiation as well as heterogeneous chemistry. The present paper provides preliminary results of simultaneous measurements of ozone and aerosol, carried out at Thule, Greenland, during the winter 1991-92. The European Stratospheric Ozone Experiment (EASOE) was aimed at monitoring the winter Arctic stratosphere in order to obtain a deeper insight of the ozone destruction processes taking place in the polar regions. A large amount of aerosol was injected into the lower stratosphere by the recent eruption of Volcano Pinatubo. A lidar system, already operational in Thule since November 1990, has provided detailed measurements of the stratospheric aerosol concentration during EASOE. In the same period, a large number of ozonesondes were launched. Although no PSC formation was detected over Thule, the simultaneous measurement of the stratospheric aerosol and ozone profiles give the possibility to study interactions occurring in the stratosphere between these two constituents.

Digirolamo, P.↗
NASA NTRS1992

L625 Lidar Measurements of Pinatubo Volcanic Cloud at Hefei

The Pinatubo volcano erupted violently between June 9-17, 1991. This eruption was much larger than the El Chichon volcanic eruption in April, 1982. Because of the effects on the global environment, much attention was focused on the measurements of the volcanic cloud. The 84 scattering-ratio profiles of the volcanic cloud have been obtained by our L625 lidar system. The conclusions from studies of the data are: (1) Pinatubo volcanic cloud was present over Hefei after 40 days from eruption; (2) the peak scattering ratio varied violently in July and August of 1991; (3) the height of the peak scattering ratio is between about 18 to 25 km; and (4) since August 28, 1991, the optical depth was about one order of magnitude larger than before the eruption.

Hu, Huanling↗
NASA NTRS1992

Wind Measurements from 15 to 50 Km with a Doppler Rayleigh Lidar

The possibility to measure the mean wind in the high stratosphere using a Doppler Rayleigh lidar was demonstrated in 1989, and the Observatory of Haute Province (44 deg N, 6 deg E). It was originally developed to cover the height range 25-60 km, a region where the radars cannot operate; therefore, the system was designed to cover altitudes where the signal is only due to the Rayleigh backscattering. The instrument is currently set up at the Center d'Essais des Landes (44 deg N, 1 deg W) where it operated during the Dynamic Adapted Network for the Atmosphere Campaign in 1990. As the contribution of the Mie scattering was very low during this period above southern France, we have obtained vertical wind profiles in the stratosphere down to 15 km. Since the eruption of the Pinatubo volcano in Jun. 1991, the contribution of Mie scattering has increased between 15 and 30 km and it was very difficult with the original system to obtain wind measurements below 30 km. We will show that by using the same method with slightly different characteristics of the system, it is possible to measure the wind in the presence of Mie scattering. The first experimental results are presented.

Garnier, A.↗
NASA NTRS1991

Graben and extension in northern Tharsis, Mars

A morphometric analysis of north-south trending graben at 35 deg N in northern Tharsis is used to provide the first quantitative measurements of crustal extension in and strain for areas of the Martian crust that have undergone both extreme and mild deformation. These estimates also demonstrate the viability of the Viking data for making such quantitative assessment. Graben in the region accommodate about 8 km of post Early Amazonian east-west extension. This extension corresponds to a net regional strain of 0.45-0.61 percent; local strains vary from less than 1 percent to 5 percent. Extension is nonuniform and localized near 110 deg (south of Alba Patera and north of Ceraunius Fossae) because of reactivation of preexisting fractures in underlying basement and possibly due to superposition of stress fields from Tharsis and Alba Patera. A major mechanical discontinuity in the shallow crust, probably representing the base of or a strength contrast within the megaregolith, is observed. It occurs at a depth of 2 km on the profile flanks and is depressed to about 7.5 km near 110 deg due to loading of the crust by the volcano.

Plescia, J. B.↗
NASA NTRS1991

General patterns of flow field growth - Aa and blocky lavas

Lava flowfields consist of one or more flows. Four ideal emplacement regimes are recognized: that for single flows and that for flowfields dominated by (1) widening, (2) thickening, or (3) lengthening, as a result of generating new flows. Most aa and blocky lavas belong to the flowfield widening or single-flow regimes. These two regimes are analyzed assuming advance is controlled by the distal core of a flow, where motion is treated as steady, uniform, and laminar. Because of low deformation rates, the distal core is also approximated to a Newtonian fluid. Widening and, possibly, lengthening are ultimately limited by crustal resistance. After a critical cooling interval, new flows are generated from the upper reaches of the flowfield. A simple relation is derived linking flowfield dimensions and underlying slope to eruption duration, independent of terms involving gravity or lava chemistry and rheology. The relation well describes field data from several volcanoes (involving lava compositions from K phonolitic tephrite to dacite). This supports the premise that the overall growth of aa and blocky flowfields is systematic and also suggests that such growth may be predictable at timescales greater than, or similar to, the emplacement times of major flows.

Kilburn, Christopher R. J.↗
NASA NTRS1992

Mt. Pinatubo SO2 column measurements from Mauna Loa

Absorption features of the nu sub 1 band of SO2 are identified in high-resolution IR solar-absorption spectra recorded from Mauna Loa, Hawaii, on July 9 and 12, 1991, shortly after the arrival of the first eruption plume from the Mt. Pinatubo volcano. A total SO2 vertical column amount of (5.1 +/- 0.5) x 10 exp 16 molecules/sq cm on July 9 is retrieved based on nonlinear least-squares spectral fittings of 9 selected SO2 absorption features with an updated set of SO2 spectral parameters. A SO2 total-column upper limit of 0.9 x 10 exp 16 molecules/sq cm deduced from measurements on September 20-24, 1991, is consistent with the dispersion of the SO2 cloud and the rapid conversion of the SO2 vapor into volcanic aerosol particles.

Goldman, A.↗
NASA NTRS1992

Stratospheric temperature increases due to Pinatubo aerosols

Northern-Hemisphere stratospheric temperatures at 30 and 50 mb beginning in June 1991 are compared with 20-year (1965-1984) and 26-year (1964-1989) monthly means. Significant temperature increases are shown in July, August, September, and October for latitudes from approximately 30 deg N to the equator. In September and October deviations are observed for large areas between the equator and 30 deg N, with temperature increases as high as + 3.5 C occurring at some locations. The monthly averaged zonal mean 30-mb temperatures at 20 deg N in September and October were approximately 2.5 C higher that the 26-year mean, with some daily zonal mean increases of almost 3 C. Higher values occurred equatorward of 20 deg N. These warmings are due to absorption of radiation by the aerosols produced from the June eruptions of the volcano Pinatubo (15.1 deg N, 120.4 deg E) in the Philippines. Stratospheric warmings are expected to be occurring simultaneously at southern latitudes, especially from the equator to about 20 deg S, based on satellite and lidar measurements of the locations of the new aerosol layers. These localized temperature increases should decrease in magnitude and become more global as the cloud disperses globally and spreads in altitude.

Labitzke, K.↗
NASA NTRS1991

Earth observations during Space Shuttle flight STS-31: The earth from 600 km - April 24 through 29, 1990

Images taken aboard the Space Shuttle flight STS-31 are presented and discussed in terms of documenting key features and describing regional interrelationships. The images comprise regional views and continuous swath maps that are intended to serve as linkage and/or context for related photographs in the shuttle database. The Linhof hand-held mapping camera is employed at 20-s intervals resulting in contiguous swaths with 75-percent overlap, and Hasselblad images are taken simultaneously to complement the swaths. Specific examples of the products are given for regions including Lake Eyre, Australia, Madagascar, and Central America; specific landforms are also shown including the El Chichon volcano, and an example is shown of the differential heating of land and water. The photographs are considered useful for mapping large-scale features and for providing context for smaller image-data products.

Evans, Cynthia A.↗
NASA NTRS1992

Magma reservoirs and neutral buoyancy zones on Venus - Implications for the formation and evolution of volcanic landforms

The production of magma reservoirs and neutral buoyancy zones (NBZs) on Venus and the implications of their development for the formation and evolution of volcanic landforms are examined. The high atmospheric pressure on Venus reduces volatile exsolution and generally serves to inhibit the formation of NBZs and shallow magma reservoirs. For a range of common terrestrial magma-volatile contents, magma ascending and erupting near or below mean planetary radius (MPR) should not stall at shallow magma reservoirs; such eruptions are characterized by relatively high total volumes and effusion rates. For the same range of volatile contents at 2 km above MPR, about half of the cases result in the direct ascent of magma to the surface and half in the production of neutral buoyancy zones. NBZs and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on Venus than on earth. For a fixed volatile content, NBZs become deeper with increasing elevation: over the range of elevations treated in this study (-1 km to +4.4 km) depths differ by a factor of 2-4. Factors that may account for the low height of volcanoes on Venus are discussed.

Head, James W.↗
NASA NTRS1991

Caldera-structure relationships in Kenya - Observations from satellite data

Maps were constructed showing lineaments displayed on four Landsat MSS images, to study volcanic-tectonic relationships in the Kenya segment of the Gregory or eastern sector of the East African rift system. Many of the mapped lineaments correlated well with fractures shown on geological maps. Selected lineaments, transverse to the rift trend, could be extrapolated to intersect rift faults at locations correlative with the locations of Kenya's seven volcanic calderas. The volcano-genetic difference between these intersections vs. similar intersections having no obvious relationship to any type of volcanic vent is not yet understood.

Blodget, Herbert W.↗
NASA NTRS1992

Observations of reduced ozone concentrations in the tropical stratosphere after the eruption of Mt. Pinatubo

Two independent sets of data, one of aerosols from an airborne lidar system, and one of ozone from ozonesonde measurements indicate that significant ozone decreases may have happened as a result of the injection of debris by the Mt. Pinatubo volcano in June 1991. The amount of this reduction maximizes at 24-25 km, near the peak of the aerosol distribution, though a deficit is seen throughout the lower stratosphere between 19 and 28 km. The greatest differences observed prior and subsequent to the eruptions at these altitudes is 18-20 percent.

Grant, W. B.↗
NASA NTRS1992

Evidence for liquid-phase cirrus cloud formation from volcanic aerosols - Climatic implications

Supercooled droplets in cirrus uncinus cell heads between -40 and -50 C are identified from the First International Satellite Cloud Climatology Project Regional Experiment polarization lidar measurements. Although short-lived, complexes of these small liquid cells seem to have contributed importantly to the formation of the cirrus. Freezing-point depression effects in solution droplets, apparently resulting from relatively large cloud condensation nuclei of volcanic origin, can be used to explain this rare phenomenon. An unrecognized volcano-cirrus cloud climate feedback mechanism is implied by these findings.

Sassen, Kenneth↗
NASA NTRS1992

Volcanic winter and accelerated glaciation following the Toba super-eruption

Model calculations that investigate the possible climatic effects of the Toba volcanic cloud are presented. The increase in atmospheric opacity might have produced a 'volcanic winter', followed by a few years with maximum estimated annual hemispheric surface-temperature decreases of 3-5 C. The eruption occurred during the stage 5a-4 transition of the oxygen isotope record, a time of rapid ice growth and falling sea level. It is suggested that the Toba eruption may have greatly accelerated the shift to glacial conditions that was already under way, by inducing perennial snow cover and increased sea-ice extent at sensitive northern latitudes. As the onset of climate change may have helped to trigger the eruption itself, it is proposed that the Toba event may exemplify a more general climate-volcano feedback mechanism.

Rampino, Michael R.↗